990-9400
EXPERIMENTS IN TECHNIQUES
OF INFRARED SPECTROSCOPY
by
R. W. Hannah
. J . S. Swinehart
PERKIN- ELMER 990-9400
EXPERIMENTS IN TECHNIQUES OF
INFRARED SPECTROSCOPY
by
R.W. Hannah
J. S. Swinehart
Perkin-Elmer Corporation Infrared Applications Laboratory Rev. September 1974
TABLE OF CONTENTS
Introduction .•..••••••....•.•....•..•...•...•..•.•..•.•.......•. Instrumentation. • • . . . . . . • • • • • • • . . • • . . • . • . • . . . • • • . • . . . . . • . • • • • ii Qualitative Analysis..........................................
11 Quantitative Analysis. • • • • • . . . • . . • • • • . • . . • • • • • . . . . . . . . • • • . . . . .
iii Variation of Spectra with Structure and Composition ....•....•... iii Interpretation of Infrared Spectra. • • • . • • . . • • . . . • • • • . . . . . • . . . • . .
vi References. • • • • • • . • . . . • • • • • . . • . • • . . . . • . • • . . • • . . . . . . . . • • . • . • .
xii Experiment 1 - Instrument Operation and Calibration.. . . . . ...•••. . •
1-1 Experiment 2 - Care and Handling of NaC1 and KBr Crystal Windows..
2-1 Experiment 3 - Determining the Thickness of a Sealed Cell and of a Polymer Film. . . . . . • • . . . . • • • • • . • • • • • • • . . .
3- 1 Experiment 4 - Spectra of Pure Liquids. • • • • • • . . . • . • • • • . . • . . . • . . . .
4- 1 Experiment 5 - Spectra of Liquids and Solids in Solution ...••••••••.
5- 1 Experiment 6
Spectrum of a Solid and Preparation of a Mull .,.....
6-1 Experiment 7 - Spectra of Solids - the KBr Disc Technique. . . . . • • • . .
7-1 Experiment 8 - Spectrum of a Solid Prepared as a Film from Solution ...••....••.•••••••...•..•••••••...•
8- 1 Experiment 9 - Quantitative Analysis ..............................
9-1 Appendix 1 - Absorption in Different Regions of the Infrared
Spectrum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
Al-l
NRC Bulletin No. 6 - Infrared Spectra of Organic Compounds:
Summary Charts of Principal Group
Frequencies
9/74
LIST OF ILLUSTRATIONS
Figure 1
The electromagnetic spectrum........................... i 2
Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene............................ i v 3
Types of vibrations ..•.•••......•.•......•..•.•.••••..• iv 4
Absorption in different regions of the spectrum . . . . . . . . vi 5
6
7
Infrared absorption spectrum of C H
0 in a 0.025
S 12
rom cell •...••.........•.....••.......•.••......•.......
ix Infrared absorption spectrum of a liquid with a molecular weight of 84
run in a 0.025 rom cell ....... x Infrared absorption spectrum of C H 0Cl in a 0.025
rom c e l l . . . . . . . . . . . . . . . . . . . . . . . . . .8. .7
. . . . . . . . . . . . . . . . . . . . xi 1-1
IO baseline •......•..•....•..•........•..•.......•..... 1-2 1-2
Polystyrene calibration sample spectrum (0.05 rom film). 1-3 2-1
Correct way to polish crystal materials for infrared sample cells ......•.•••...•.....•...•......•..•••..•..• 2-3 2-2a
Spectrum of clean sodium chloride window 4 rom thick .... 2-3 2-2b
Spectrum of clean potassium bromide window 4 rom thick •. 2-4 2-3
spectrum of 4 rom thick sodium chloride window with residual Linde type 0.05 B Alumina polishing compound •• 2-4 2-4
Cleaving a sodium chloride crystal •..••........•.....•• 2-5 -2-5
Cleavage planes of a crystal window ..•.•.•.•.••..•.••.. 2-5 3-1
Path of radiation between the inner surface of a film or cell ..•...•••••...•.•.•.•••.•.•••..••••••....•.•..•• 3-2 3-2
Wave patterns for transmitted and reflected portions of radiation when cell thickness, d, is such that 2d = mA, the in-phase condition for a fringe maximum •••••.•.•..• 3-2 9/74
LIST OF ILLUSTRATIONS (CONTID) Figure 3-3
Fringe pattern obtained for an empty 0.1 mm thick sealed KBr cell.. . . . . . . . . . . . . . . . . . . . . . • • • . . . . . . . . . . . . • . . ..
3- 3 Fringe pattern obtained with the 0.05 rnrn thick poly­
styrene calibration sample. . ...•••.•.•••• .... ..•.••.•..•. ..
3-4 4- 1
Cor rect way to fill a sealed cell. • • . . . • • • . • • • • • • • . . • • . . . • • ••
4- 2 4- 2
Carbon tetrachloride spectrum, O. 1 rnrn sealed cell. • • . • • . . ..
4- 2 4- 3
Carbon tetrachloride spectrum of reduced intensity becaus e of bubbles in sealed cell (0. 1 mm sealed cell) •.•.•.•••••.....
4-3 4-4
Use of two syringes to clean cells less than 0.075 mm thick ..•
4-3 4- 5
Carbon disulfide spectrum, O. 1 rnrn sealed cell. . . . • . . • • . . • •.
4- 4 4-6
Demountable cell ass.embly diagram... . .••. •. . .. • •. • • .•••..
4-4 4-7
Indene spectrum 0.05 rnrn demountable cell ...•••••••..•.••.
4-6 4- 8
Spectrum of mineral oil capillary film run in demountable cell. . • . . . . • . . . • • . . • . • • . . . . . . • . . . . . . • • • • . • • • ••
4- 6 Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell••••••••••••••.•••••••••..••••••••••••.•.• ,
4-6 4-10 Spectrum of silicone grease smear run in demountable cell. . •.
4-7 5- 1
Spectrum of pure toluene run in 0.025 mm sealed cell .•..••..
5- 3 5- 2
Spectrum of 20% weight-to-volume polystyrene in xylene run in a 0.025 mm demountable cell ..••.•.........••.•.••..
5-4 6- I
Spectrum of talc mulled in mineral oil .....••...•••.....••.•
6- 2 6-2
Typical band distortion resulting from Christiansen scattering. • . • . . • • • • • • • • • • . • • • • • • . . • • • • • • . • . . . . . . • • • • • • • •.
6- 3 6- 3
Spectrum of 2,4- dinitrophenylhydrazine mull ..•.••••••..••••
6- 4 6-4
Spectrum of 2, 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering. • • • • • • • ••
6- 4 Spectrum of phthalic anhydride mulled in perfluorohydrocarbon ....••••••••••••••••••••••••••.••••••
6- 5 3-4
4-9
6- 5
9/74 LIST OF ILLUSTRATIONS (CONT'D) Figure 6-6
Spectrum of phthalic anhydride mulled in mineral oil
6-5 6-7
Spectrum of sodium bicarbonate mulled in mineral oil ...•.•.•
6-6 7-1
Spectrum of potassium bromide disc blank •.......•...•.••••
7-2 7-2
Spectrum of benzoic acid in potassium bromide disc
7-3 7- 3
Spectrum of benzoic acid in potassium bromide disc showing band distortions caused by poor grinding....................
7-3 7-4
Spectrum of quartz in potassium bromide disc...............
7-3 8- 1
Spectrum of polystyrene cast film ••••••.•..•....••.•••••...
8- 2 9-1
Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale ............... , . . . . . . . ..
9-2 9-2 A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale, . . . . ..
9-2 9-3 10 for complex absorption bands, Dotted lines show exten­
sion of bands in an assumed symmetrical Lorentzian
9-4 9-4 Spectrum of neat toluene in a O. 015 mm KBr cell .. , ..
9-5 9-5 Spectrum of neat 2 - isopropyl alcohol in a 0.015 mm KBr cell. ... " . . .. .. .. . .. .. .. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . ..
9-5 9-6 Spectrum of neat methyl ethyl ketone in a 0.015 mm KBr cell. , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9-6 9-7 Spectrum of solution containing 15% isopropyl alcohol, 55% toluene, and 300/0 methyl
ketone in a 0.025 mm cell. . . . . .. 9-6 9-8 Spectrum of solution containing 20% isopropyl alcohol, 45% toluene, and 35% methyl ethyl ketone in a 0.025 mm cell. . . . . ..
9-6 9-9 Spectrum of solution containing 25% isopropyl alcohol, 44% toluene, and 31% methyl ethyl ketone in a 0.025 mm cell. .. .. ..
9-7 9/74 LIST OF ILLUSTRATIONS
Figure
9-10 Spectrum of solution containing 350/0 isopropyl alcohol, 20% toluene, and 45% methyl ethyl ketone in a 0.025 mm cell. .. , ..
9-7 9-11 Spectrum of solution containing 50% isopropyl alcohol, 14% toluene, and 36% methyl ethyl ketone in a 0.025 mm cell. . . . ..
9-7 9-12 Plot of volume percent isopropyl alcohol vs. absorbance obtained from 817 cm- 1 absorption band in Figs. 9-7 through 9-11 .................. ' ..........................
9-8 9-13
Plot of volume percent toluene vs. asorbance obtained from 695 cm- 1 absorption band in Figs. 9-7 through 9-11. .........
9-8 9-14 Semilog plot of percent T vs. volume percent isopropyl alcohol as obtained from 817 em -1 absorption bands in Figs. 9-7 through 9-11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
9-9 9/74
INTRODUCTION
Note: The experiments described in this manual are intended to be
to aid operators in learning the operation of infrared instru­
mentation and the basic techniques of sample handling. Though they
are written for the Perkin-Elmer Model 735 infrared spectrophoto­
meter, they may be applied to any infrared instrument by extrapola­
tion with the specifications of that specific instrument.
Infrared is the portion of the electromagnetic spectrum that extends
beyond the visible into the microwave region (Fig. 1). It is measured in
units of frequency or wavelength. In the infrared, frequency is usually
expressed in wavenumber units, or reciprocal centimeters (cm- l ), which
are the number of waves ,fer centimeter. Wavelength is expressed in
microns (10- 3 mm or 10- cm). abbreviated,... Frequency, f, and wave­
length, A., are related by the equation fA. • c, where fre~uency is defined
as cycles per second and c is the velocity of light 3 x 10 0 cm/sec}. A
wavenumber unit, v. is defined as the reciprocal of wavelength (v • 10 4 /A.).
The product of v and c gives the frequency in cycles/sec. The infrared
region extends from approximately 0.75 JJ. to almost 1 mm, but the segment
most often used by the chemist is from 4000 to 400 cm- l (2.5 to 25 JJ.) termed
the "fundamental" region. The low frequency region from 600 cm- 1 to
200 cm- l , the extended range and the range from 200 cm- l to the microwave
region are often called the far infrared. The region from 4000 cm- 1 to the
visible is often called the ne,ar infrared or overtone region.
All molecules are made up of atoms held together by chemical bonds.
These atoms vibrate with respect to each other, the bonds acting much like
springs connecting the atoms. Each molecule has its own specific set of
vibrational frequencies, but different molecules have different sets of
vibrations. The frequencies of these vibrations are in the same range as
the infrared frequencies of electromagnetic radiation.
Vfavemunber
10 13
10 10
108
10·
1~6
1.'
10 2
2.5'10 5 1.42' 10 5
650
4000
12
s· lO"~
10- 3
10- 6
1.5.10- 3
S--lO~6
lO~7
10- 10
{em-l}
Energy,
.lectron volta
lfiI
15
0.'
Z.5
7.
1O~2
15.4
830
Fig. 1 - The electromagnetic spectrum
9/74
ii
Infrared analysis gives the scientist a permanent, step- by- step record
of his work, providing him and his organization with evidence of the dates on
which he reached various stages, a record which can be invaluable in patent
applications. In carrying out a complex synthesis, he can determine the
identity and purity of reagents, follow stepwise changes in all materials, de­
termine percent yields, and can check back at any stage. Furthermore,
there is no fear of having insufficient sample to proceed to the next stage,
since infrared analysis is nondestructive aiJ.d the sample is recoverable.
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by
passing infrared radiation through it and recording which wavelengths have been
absorbed and to what extent. Since the amount of energy absorbed is a function
of the number of molecules present, the infrared instrument provides both
qualitative and quantitative information. The recorded spectrum is a plot of
the transmittance of the sample versus the frequency (or wavelength) of the
radiation. This spectrum is a fundamental property of the molecule and can
be used both to characterize the sample and to determine its concentration.
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its
most characteristic physical property, infrared finds extensive application
in "fingerprinting" or identifying materials. By matching the infrared spec­
trum of an unknown with that of a known material, proof of identity is estab­
lished. A library of spectra of the materials most frequently encountered
can be accumulated, or reference spectra available commercially from vari­
ous sources can be purchased. Identification then becomes a matter of sort­
ing and matching.
The infrared spectrum contains basic information about the composition
and structure of a compound. Organic compounds, for example, may contain
groups such as -OH, -NH2' -CH3, -CO, -CN, -C-O-C-, -COOH, -CS, etc.
These groups have characteristic absorption frequencies in the infrared which
are usually relatively unaffected by the remainder of the molecule. When
they are affected by the rest of the molecule additional information about
its structure can be obtained. An unknown compound, therefore, can often
be characterized by observing the presence of the absorption frequencies
associated with such groups. Spectra-structure correlation charts like the
ones with this manual provide a key to the location of characteristic absorp­
tion bands for most of the common functional groups. With them, the investi­
gator can quickly determine the gross structural features of an unknown by
band identification and reduce the number of possibilities so that matching
the unknown to a library of reference spectra can be done in a matter of
minutes. If, however, the investigator does not have access to a reference
9/74
spectrum for the compound under investigation, he can often identify it by
functional group analysis together with a few easily determined physical and
chemical properties. See the interpretation section for examples of this.
A great advantage of infrared to the scientist is that the spectrum is
interpreted in terms of the same concepts he uses in studying chemical prop­
erties, bonds and bond groupings. Characteristic absorption bands in the spec­
trum provide information regarding the chemical nature of the sample. The
investigator can apply his knowledge of chemical bonding to his interpretation
of the spectrum. He can quickly use infrared without having to learn an en­
tirely new language.
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of
chemical mixtures. Since the depth of an absorption band is proportional to
the concentration of the component causing that band, the amount of a com­
pound present in a sample can be determined by comparing the depth of that
band with its depth in a spectrum from a sample containing a known concentra­
tion ,...f the material. Usually, the spectra of a few samples with known con­
centrations of the compound are obtained to provide a working curve of absorb­
ance vs. concentration from which the concentration of the unknown may be
easily determined. The spectrum of a mixture is usually a superposition of
the spectra of the pure components. Absorption wavelengths unique to each
component are chosen and the sample transmittance at the chosen wavelengths
is measured and related to the component concentrations.
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose
molecules have a vibrational frequency the same as that of the incident radia­
tion, the molecule absorbs radiant energy, and the energy of the molecule is
increased. If the incident frequency differs fro:m the characteristic frequen­
cies of the molecule, the radiation passes through undi:minished. The char­
acteristic frequencies for a particular :molecule are determined primarily by
the masses of the atoms in the molecule and the strength of the bonds connect­
ing the:m. Furthermore, the proximity and spatial geometry of various groups
may often influence their vibrations.
If a pair or group of atoms is to absorb infrared radiation, it must
undergo a change in dipole (dipole moment) during the vibration. The
changing dipole couples the vibration of the molecule with that of the
radiation much as air (or any other fluid) between two fans couples the
motion of one fan with the other. If an unconnected fan is placed opposite
a moving fan in a vacuum. the unconnected fan will not move. If air is
admitted to the system it "couples" the motion of the moving fan to that
of the unconnected fan, which ideally rotates at the same frequency as
the fan to which power is supplied.
9/74
iv
H
H
'" '"
/
C
H
H
C
/
Cl
'"
/
c
C
H
H
The two carbon ato:ms have
sa:me charge; stretching vi­
brations produce no change
in dipole :mo:ment.
/
'"
H
Presence of chlorine alters charge
distribution so that the carbon ato:ms
have a s:mall but significant difference
in charge density. Carbon stretching
vibrations cause a change in dipole.
Fig. 2 - Stretching of carbon-to-carbon double bonds in
ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig. 2)
does not absorb infrared radiation because there is no change in dipole during
the vibration. This inactivity of a vibrational frequency often occurs when the
vibrating group lies at or neara center of sy:m:metry within the :molecule. The
stretching of the carbon-carbon double bond in chloroethylene causes a signifi­
cant change in dipole :mo:ment, and this double bond has a strong infrared ab­
sorption. The changing dipole couples the electro:magnetic radiation with the
vibrating carbon ato:ms.
Molecular vibrations can be classified as stretching or bending vibra­
tions (Fig. 3). The latter are so:meti:mes called defor:mation and are sub­
classified into scissoring, wagging, twisting, and rocking. The frequencies
of the stretching and the bending vibrations, like the frequencies of all
.~.
Bending or Deformation
.
Stretching
o
0
~/,-
T
o
0
~~
i
Aayrmnetric
Synunet:r:ic
Stretching
Stretching
0
0+
0+
X( '"T "'/i
0
0
+0
/
Scissoring
Twisting
Fig. 3 - Types of vibrations
9/74
Wagging
0
XX
i
Rocking
0
:mechanical oscillators, are dependent upon the :masses of the vibrating
units (ato:ms or groups of atoms) and the stiffness of the spring-like con­
nections (chemical bonds) joining the vibrating units. Stretching vibrations
always have a higher
than the bending vibrations of the same group.
The lower the masses of the atoms, the higher the frequency of vibration.
The "stiffer" the bond, the higher the frequency of vibration. A bond's
"stiffness" or its force constant is roughly proportional to bond strength,
which in turn is roughly proportional to the bond order. That is, for groups
with ato:ms of the sa:me mass, a triple-bonded group has a higher vibrational
frequency than a double- bonded group, and the double- bonded group has a
higher vibrational frequency than a single- bonded group. A group bonded
with a single bond that has partial double- bond characteristics, such as often
results fro:m resonance, has a vibrational frequency inter:mediate between
those of the sa:me group with "pure" double and single bonds.
Vibrations of groups where one ato:mic nucleus is a proton have the
highest frequencies of all :molecular vibrations. All stretching vibrations of
hydrogen ato:ms occur abqye 2250 cm- l • No other groups have fundamental
absorptions in this regi~n although overtones fro:m lower frequency vibrations
are someti:mes observed above 2400 cm- l . Groups with triple bonds absorb
in the next highest region of the spectrum, from 2300 to 2100 c:m- l • The only
other principal'group to have fundamental absorptions in this region are those
with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O. Cumulated double
bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l )
because of coupling between th~ cumulated bonds.
Coupling, or mechanical interaction, occurs when two groups having
si:milar frequencies are close to each other in the same molecule. In effect,
resonance is established between the two vibrating groups, and vibrational
energy flows back and forth between them so that the vibrations of the two
groups :modify each other. Another way of viewing this is that the coupling
groups lose their individual vibrations and vibrate together. Coupling is
strongest when the two interacting groups share a common atom and the fre­
of the two groups are very close or identical.
Carbon dioxide is such a :molecule. The stretching frequencies of
most carbonyl groups is so:mewhere near 1700 cm-1 In carbon dioxide the
two carbonyl groups vibrate together with the asymmetrical vibration occur­
ing at 2350 cm- 1 and the symmetrical vibration occurring at approximately
1330 cm- l • The symmetrical vibration is actually a complex, widely spaced
doublet because of Fermi resonance with an overtone from a bending vibra­
tion. The sy:m:metrical vibration does not cause an infrared absorption be­
cause no change in dipole occurs. The regions for the various vibrations
are summarized in Figure 4.
9/74
vi.
FREQUENCY ICM ')
2800
2400
2000
1800
1600
1400
1200
1000
800
650
Fig. 4 - Absorption in different regions of the spectrum. For use
in identification of various groups in spectra of unknowns, this chart
is included, full size, at the back of this manual as Appendix 1.
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared
spectra. For facile, good interpretation one needs a thorough understanding
of the principles outlined above, an infrared cor relation chart, a reasonable
knowledge of structural organic chemistry (and inorganic chemistry if inor­
ganic compounds are to be examined), and experience. The first two are pro­
vided with this manual. The third can be obtained by a formal introductory
course in organic chemistry such as almost all scientists study as part of
their undergraduate curiculum.
There is, of course, no short cut to experience. The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning. More experience can be obtained from the references listed after the problems, from the short infrared interpretation courses offered at various universities, and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application. The first step in the interpretation of an infrared spectrum is to look
at the entire spectrum, keeping in mind any other information about the com­
pound that might aid in its identification such as source, state, boiling point,
etc. The general appearance of the spectrum usually gives clues to the
identity of the compound. The following specific regions should then be
examined:
9/74
vii
Look first at the 3800-2250 c:m- 1 ranfe for hydrogen stretching ab­
sorptions. A set of bands at 3000-2800 c:m- indicates hydrogen on saturated
carbon ato:ms, at 3100- 3000 c:m- 1, hydrogen on aro:matic, vinyl, or cyclo­
propyl carbon ato:ms. A very sharp band at 3300 c:m- l indicates the hydrogen
on a ter:minal acetylene unit (-CliCH). Other sharp bands above 3100 c:m- l
are due to unassociated hydroxyl or a:mino groups. Very broad or ill defined
bands between 3300 and 2250 c:m- l are fro:m associated -OH and NH groups.
Broad absorptions between 3000 and 2250 c:m- 1 are either fro:m OH of acids
or N-H of a:mine salts. A doublet at 2820 and 2720 c:m- 1 is fro:m the proton
on the carbonyl carbon ato:ms of aldehydes and is very characteristic of these
co:mpounds. As indicated above, absorptions fro:m 2275 c:m- l to 1930 c:m- 1
are fro:m triple or cu:mulated double bonds. Since not :much else absorbs in
this region, bands here are very diagnostic.
The double-bond region fro:m 1900 c:m- 1 to 1500 c:m- 1 should be ex­
a:mined next. Strong bands between 1900 and 1660 c:m- 1 a1:most always indi­
cate carbonyl groups, although so:me carbonyl groups such as those with ex­
tensive conjugation and/or strong hydrogen bonding, so:me a:mides, and
carboxylate salts absorb at lower frequencies. See Table V in the acco:mpany­
ing frequency correlation booklet for absorption of specific groups. The
double- bond region also includes bonds fro:m ethylenic type linkages (very
weak to moderately strong, 1685-1630 cm- 1) aromatic structures (several
from 1620-1450 cm- l ), aromatic heterocyclics (several from 1660-1490
cm- 1), conjugated dienes and trienes (one to three bands from 1650 to 1600
cm- l ) and polyenes (broad band at 1650-1580 cm- l ). The presence of these
unsaturated systems can be verified and specific structural types determined
by:
1. the exact frequency of the band;
2. the :moderate to strong out-of-plane bending vibrations between 1000 and
660 cm- l (Tables III and IV in the accompanying frequency correlation
booklet); and
3. the weak overtone combination bands between ZOOO and 1650 cm- l (Table I
in the frequency correlation booklet for aromatics and 1860-1800 cm- l for
-CH'::CHZ and 1800-1750 cm- l for '::C::CHZ)'
The next region to examine is lZ50-1000 c:m- 1• Very strong bands
here, with no other very strong bands fro:m 1580-940 cm- l , are indicative
of C-O stretch such as is found in ethers, esters, carboxylic acids and their
anhydrides, alcohols, and phenols.
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups.
A doublet here indicates a gem dimethyl or trimethyl group •. Very intense
bands between the carbonyl region and 940 cm- l are usually due to polar
9/74 viii
I
groups containing oxygen or fluorine such as -P=O, -P-O-, -N=O, -N-O-,
-8=0, -8-0-, ;C-O-, etc. Some of these bands, such as those from -NO,
-NOZ, and S03H, are the most intense of all infrared absorption bands, as
might be expected from the large changes in dipole caused by vibrations of
these groups. Strong bands below 810 cm- l are often from carbon-chlorine
stretch vibrations. Carbon-bromine and carbon-iodine stretch vibrations
are usually below 620 cm- l ,
Other absorption bands in the spectrum are useful for verifying the
general structural features indicated by the above procedure, for obtaining
information on other structural features, and for "fingerprinting" the com­
pound.
The spectra for the following examples were obtained on the Model
735 and should be essentially identical with spectra you would obtain froITl
the same sample on your instrument. It is suggested that you first look at
the spectra and the information about the compounds given in the captions.
With thes e data try to identify the compounds. Then read only the first para­
graph of the interpretation. 1£ the interpretation there is different than the
one you obtained, reevaluate the data and attempt to identify the compound
again. Then read the rest of the interpretation. 1£ you missed, try to de­
termine where your interpretati:on went astray. By following this procedure,
even if you miss every problem, you will take a big step in beginning to ob­
tain the experience that is needed to interpret infrared spectra.
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorp­
tion spectrum shown in Figure 5, A quick glance at the spectrum shows
that the strongest bands are at 3300 cm- 1 (broad), 2940-2860 cm- l , and
1060 cm- l (sharp). The broad 3300 CIn- l band indicates associated OH and
the band at 1060 cm- l is probably froIn carbon-oxygen stretching, The
2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon
atOIn. There is no absorption from olefinic or aroInatic hydrogen and there
are no other absorption bands which could be froIn unsaturated groupings,
The infrared spectrum shows that the COInpound is definitely an alkanol.
This is verified by the molecular formula, whi ch is consistent only with an
alkanol or saturated ether.
The C-O stretch at 1060 CIn- l can be from a primary alcohol with
no branching at the second carbon, -CH2CHZOH (1050 CITl- l ), or a secondary
alcohol with double branching at one carbon atOIn adjacent to the -CHOH group,
",
«
H
-/C-«-«-CHZ­
C OH
1
/1 ,
9/74
FREQUENCY (CM')
"000
3600
3200
2800
Fig. 5
2400
1800
1600
1400
1200
1000
BOO
601)
Infrared absorption spectrum of
C5HIZ0 in a 0.025 mm cell
The latter structure is inconsistent with the formula and with the spectrum
in the 1400-1100 cm- l region., With -CHZCHZOH known, three more carbon
atoms must be accounted for. The doublet around 1380 cm- 1 indicates a gem
dimethyl group. The fact that the intensity of the lower frequency band is not
considerably stronger than that of the higher frequency band indicates that the
doublet is not from a tertiary butyl group. This alone, however, does not
comyletely rule out the tertiary butyl group. Absorptions at 1175 and 1130
cm- indicate an isopropyl group although many absorptions occur in this
region which may either mask or be mistaken for the two bands that verify
an isopropyl group. In any event the only group that is consistent with this
and the other information on the molecule is isopropyl (CH3)ZCH-. This and
the -CHZCHZOH group indicate that the compound is isoamyl alcohol or
3-methyl-l- butanol, (CH3)ZCHCHZCHZOH.
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrum
shown in Fig. 6. The strong aliphatic C-H stretching near 2950 cm- l , the
deformation absorptions at 1365 and 1465 cm-l , and the lack of any absorptions
that could possibly be from functional groups show that the compound is an
alkane. An alkane of the molecular weight indicated would have six carbon
atoms and possible molecular formulas of C6H14 for a noncyclic compound,
C6H12 for a monocyclic compound, and C6HlO for a bicyclic compound.
The incompletely resolved multiplet around 1370 cm-1 indicates a
gem dimethyl group, with possibly another type of methyl group. The much
stronger low frequency absorption of this multiplet indicates a tertiary butyl
group. The tertiary butyl group is verified by the absorptions at 1255 and
1215 cm- 1 and by the weak absorption at 930 em-I. With (CHS)3C- established,
9/74
:It
4000
3600
3200
2800
2400
2000
FREQUENCY (CM'i
1800
1600
1400
1200
1000
800
600
400
Fig. 6 - Infrared absorption spectrum of a liquid with a
molecular weight of 84 !3 run in a 0.025 rnrn cell
two carbon atoms remain. These can only be arranged as an ethyl group.
This is verified by the absorption at 780 cm-l,which is probably from methy­
lene rocking. These occur at 790-770 cm- 1 for ethyl, 745-732 cm- 1 for
~-propyl, and 725-715 cm- l for four or more methylene groups in series.
This absorption not only shifts to lower frequencies with an increasing num­
ber of methylene groups but also increases in intensity. In unsaturated and
polar compounds the absorption is often not observed because it is so weak
relative to other absorptions or because it is masked by strong bands be­
tween 800 and 700 cm- l • The compound is 2, Z-dimethylbutane or neohexane,
(CH 3hCCHZ CH 3'
Example 3 - A liquid (C8H70CI) in a 0.025 mm cell gives the infrared ab­
sorption spectrum shown in Figure 7. Absorptions between 3100 and 2900
cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls.
The strong absorption at 1685 cm- l can only be from a carbonyl group. The
absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 in­
dicate an aromatic ring.
The formula and carbonyl absorption allow only an aldehyde, ketone,
or acyl chloride. The absence of a doublet at Z870 and 2720 cm- 1 argues
against an aldehyde, and acyl halides have carbonyl stretch absorption fre­
quencies above 1740 cm- l • Only a ketone remains and the 1685 CITl- 1 loca­
tion indicates a ketone conjugated with an aromatic ring. This is verified
by the strong band at 1260 em-I, The location and intensity of this band
vary enough, however, to make it not too reliable for verifying the presence
of ketone groups. It is doubtful that the halogen is alpha to the ketone group
as this usually shifts the carbonyl stretch absorption to a higher frequency
9/74
xi
FREQUENCY (CM'1
..000
3600
3200
2800
2400
2000
1800
1600
1.00
1200
1000
800
600
400
Fig. 7 - Infrared absorption spectruIn of C8H70Cl in a 0.025 InIn cell by 10 to 25 CIn- l . The bands at 1430 and 1355 CIn- 1 are consistent with a
Inethyl group alpha to a carbonyl. FroIn the above inforInation we know the
9
COInpound Inust be an aryl Inethyl ketone, ArCCH3. Consideration of the
forInula and lack of evidence for other functional groups gives a structure of
CIS{];
with only the position of the chlorine atOIn left undecided. The strongest
absorption in the out-of-plane bending region is at 833 CIn- l . This indicates
1,4- or 1,3,5- substitution. The Inolecular forInula and lack of another
strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil­
ity. The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated over­
tone-coInbination region verify para substitution. The COInpound is
.P- chloroacetophenone.
9/74
xii
REFERENCES
MONOGRAPH
Bauman, R. P.
John Wiley and Sons,
London, 1962, pp. 593
DESCRIPTION
Mainly theoretical considerations, some
instrument, accessory and experimental
information; a little interpretation. Some
ultraviolet discussions.
Barrow, G. M. The Structure of Molecules W. A. Benjamin, New York
1963, pp. 153
Simplified theoretical. About 40% infra­
red. Rotational and electronic spectra
also.
Co1thup, N. B., Daly, L. H., and Wiber1ey, S. E. Introduction to Infrared and Raman Spectroscopy Academic Press, New York, 1964, pp. 484 Most comprehensive text in this list on
theory and interpretation of vibrational
spectra.
Kendall, D. N. Applied Infrared Spectroscopy Reinhold Publishing Corporation, Chapman and Hall, London, 1966, pp. 532 Very comprehensive. Includes special
topics. Better suited for thos e with
some infrared experience.
Potts, W. J. Chemical Infrared Spectroscopy John Wiley and Sons, New York, 1963, pp. 312 Experimental techniques; spectrometer
optics and operation; basic theory;
quantitative analysis.
Interpretation Only Cairns, T., et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd., London, 1964, Volume I - 60 problems 1966, Volume IV - 60 problems Answers to problems available from
publisher. NMR, ultraviolet and infra­
red,and in Volume n, mass spectroscopy.
9/74
xiii
MONOGRAPH
DESCRIPTION
Dyer, John R.
About 300/0 infrared.
Applications of Absorption
spectra. Spectroscopy of Organic Com.pounds, Prentice-Hall, Inc.,
Englewood Cliffs, N. J.,
1965, pp. 132
Nakanishi, K.
Infrared Absorption Spectroscopy,
Holden Day, San Francisco,
California, 1962, pp. 220
Swinehart, J. S.
Introduction to Interpretation
of Spectra
Wadsworth Publishing
(in press, Jan. 1975)
Be llam.y , L. J.
Infrared Spectra of Com.plex
Molecules,
Methuen & Co LTD
NMR and ultraviolet Text, tables, and problems with answers.
All infrared.
Tables, prograIllIlled text and problem.s
with answers, 750/0 infrared.
Reference text.
London, England
(1954) pp. 425
9/74
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with
calibration of the wavenumber scale.
MATERIALS
The Model 735 instruction manual and a polystyrene film.
INTRODUCTION
The Model 735 is quite simple to operate, and will quickly produce
quality spectra. There is, however, one set of spectra which should be ob­
tained at least once a week, and more often if the instrument receives heavy
use. These spectra should be dated and kept, since they provide a continuous
record of instrument performance. Variations in these spectra can be used
as guides for modifying analytical procedures, or to detect incipient troubles.
Comparison of the most recent spectra with those obtained when the instru­
ment was new will allow quick detection of deterioration in instrument per­
formance that would probably go unnoticed for a considerable time without
such comparison.
PROCEDURE
Part I
Operation of the Instrument; Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as
described in the instrument instruction manual. Carefully align the chart
paper with the index mark on the recorder scale. The gain and balance
should be set according to the instructions in the manual.
Set the SCAN switch so it is not lit or flashing and move the recorder
to the right until the arrow points to 4000 em-I. Without a sample in either
the sample or reference beam. adjust the 1000/0 control until the pen reads
95% on the transmission scale. Start the scan by pressing the SCAN switch
and record the 10 , or baseline, as shown in Figure 1-1. It should be flat
within the specification noted in the manual.
At the completion of the scan, the SCAN switch will flash. Depress
the SCAN switch, return the recorder to 4000 cm- l , and adjust the 100% con­
trol until the pen reads 100%.
9/74
Page 1-2
FREQUENCY (CM')
./000
3000
3200
2800
2~00
2000
1800
1600
1400
1200
1000
800
AOO
Fig. 1-1 - 10 baseline
Adjustment of the 1000/'0 control for a 1000/'0 transmission reading with
no saITlple in the spectrophotoITleter has been found to be the most generally
useful setting for running spectra of saITlples, particularly unknown samples.
This setting will prevent the pen from running off the chart above 1000/'0, with
possible loss of spectral inforITlation. If an occasional saITlple has low trans­
ITlission overall, a second spectrUITl with the 1000/0 control adjusted for maxi­
ITlum utilization of the transITlission scale =ay be obtained. Even this ITlay
not always be necessary, for a good spectrum is, by definition, one which
yields the desired inforITlation.
Part II
Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 1000/'0 control adjusted for a 1000/0 transInlssion reading, place
the polystyrene calibration saITlple in the saITlple holder of the instrument and
scan the spectrUITl of polystyrene on the saITle piece of chart paper used for
the 10 scan froIn 4000 to 400 CIn-l. ReITlove the chart paper from the recorder
as described in the instruction Inanual, and fill in the appropriate inforInation
on the upper part of the chart.
The spectruITl of polystyrene contains a convenient set of absorption
bands which =ay be used to verify the calibration of the frequency scale of
the instrument. These peaks are nu=bered in Figure 1- 2, and their positions
should be cOITlpared with the frequencies tabulated below. The experiITlentally
deterITlined frequencies should agree with the tabulated values to within ± 8 cm- l
from 4000 to 2000 CITl- I and within±4cm- 1 from 2000 to 400 em-I.
9/74
Page 1- 3
FREQUENCY (CM')
4000
3600
3200
2800
2400
2000
ISoo
1600
1..00
1200
1000
800
600
Fig. 1- 2 - Polystyrene calibration sample spectrum (0.05 mm film)
PEAK #
1
2
3
4
5
6
7
8
9
10
11
FREQUENCY, cm- l
WAVELENGTH, p
3027
2851
1944
1802
1601
1495
1181
1154
1028
907
699
3.30
3.51
5.14
5.55
6.25
6.69
8.47
8.67
9.73
11. 02
14.31
9/74
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning, polishing,
and cleaving optical grade NaCl and KBr windows to be used in
infrared analysis.
MATERIALS
For Cleaning: Solvent for the sample material which will not
affect the crystal.
For Polishing: Finger cots or rubber gloves, and Perkin-Elmer
Crystal Polishing Kit (186-0429).
For Cleaving: Razor blade and small hammer.
INTRODUCTION
The care and handling of the crystal windows used in demountable
cells and demountable sealed cells is critical to the quality of any infrared
analysis. Window fogging, caused mainly by etching of the window surfaces
by water vapor, may result in a sloping baseline or in excessive reduction
of the energy transmitted by the cell. Sample residues occluded on window
surfaces may absorb energy in a way which will seriously hinder the interpreta­
tion of other spectra or reduce the accuracy of quantitative analyses. These
difficulties can be overcome by keeping the windows clean and dry, and by
polishing them when necessary using the procedures described.
Furthermore, windows that are cracked or broken may still be useable.
Large pieces may be found suitable for running samples harmful to the
crystal material, where it is not desirable to ruin a good window. Smaller
pieces can be cleaved as described and used in microsampling cells.
Table I lists properties of crystal materials which are important
as aids to maintaining and handling cell windows.
9/74
Page 2-2
Table I
Properties of Crystal Materials
Crystal
Useful Range
(cm-l)
Water Solubility
{g/100 cc H2O)
Other Properties
NaCl
10,000-650
35.7
Cleaves and polishes
easily.
KBr
10,000-400
53.8
Cleaves and polishes
easily.
CaF2
10,000-lllO
0.0017
Does not cleave, dif­
ficult to polish.
BaF2
10,000-760
0.17
Obtained as sawed
blanks, moderately
easy to polish.
Irtran-2
10,000-715
Insoluble
PROCEDURE
Glasslike, withstands
severe thermal shock.
Difficult to polish.
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned
easily by washing with a solvent (not water) for the film or sample on the
window. However, if the sample is insoluble, or if the crystal surface has
become fogged or scratched, it may be necessary to polish the crystal as
described below. If the window is merely fogged, omit grinding on the sand­
paper and proceed to the polishing operation.
Part II - Grinding Cell Windows
When the polishing kit is being used, follow the directions below.
The grinding operation is carried out on one of the ground glass plates.
A small amount of abrasive is poured on the-plate and enough ethyl alcohol
is added to make a slurry.
To grind the surface of a crystal, use strokes 3 to 4 inches long
preferably in a figure eight pattern. After 10 to 15 strokes, rotate the
crystal 90 and use an additional 10 to 15 strokes to obtain even wear. The
plate should not be allowed to dry. A very small amount of grinding com­
pound will polish several crystals.
Use no. 400 abrasive for rough grinding and no. 600 for fine grinding.
Wash the glass plates before changing abrasives. Scratches can occur from
unclean abrasive.
9/74
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing
pad on one of the ground glass plates.
Mix a slurry of Barnsite and water
and brush onto the back third of the
pad. (Other polishing compounds are
available such as Linde metallographic
polishing compound.) Rub the crystal
in a brisk manner. gradually working
toward the dry portion of the pad.
About 25 strokes should be enough to
polish the surface and 10 or so strokes
to buff on the dry portion of the pad.
Fig. 2-1 - Correct way to polish crystal
Wipe the edges of the crystal with a
materials for infrared sample cells
dry rag.
Inspect the window surfac'e to see whether additional polishing is required.
The surface should be clear and free from scratches. A small amount of
"orange peel" may be evident; tp.is is acceptable if barely noticeable. If no
further polishing is needed, grind and polish the other side of the window.
Mter both sides of the window have been polished, obtain a spectrum
of the window to detect any residual polishing compound which might remain
on the window. The spectrum of a clean NaCl window is shown in Fig. 2-2a
and the spectrum of a clean KBr window is shown in Fig. 2-2b. If the spectrum
FREQUENCY (CM')
<1000
3600
3200
2800
2400
2000
1800
1600
IAoo
1200
1000
800
Fig. 2-2a - Spectrum of clean sodium chloride window 4 mm thick
9/74
600
Page 2-4
FREQUENCY (CM ')
.000
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
Fig. 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound, as shown in Fig. 2-3,
wipe the window carefully on a clean portion of the polishing cloth moistened
with alcohol. Wipe carefully on a clean, dry portion of the cloth. Rerun
a spectrum of the window.
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows
satisfactory for many qualitative and semi-micro applications. It is preferable
to prepare the smaller windows from cracked or broken plates produced as a
result of thermal shock or accidental dropping.
FREQUENCY (CM')
.000
3600
3200
gH'+H+M+H ,..L·,··I··:·'
~t+ttlrtttirttH+1
2800
2.00
2000
1800
1600
1400
1200
1000
800
600
*
"
Fig. 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
9/74
400
Page 2-5
/)
/
,///'e
I
i
~/
\'~"\;j,
!
I
\
,
I
Fig. 2-4 - Cleaving a sodium chloride
crystal
'- "­ ,
'
Fig. 2-5 - Cleavage planes
of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires
a little practice. Place the crystal to be cleaved on a flat, clean, firm surface.
Hold a single-edge razor blade parallel to one of the flat sides of the piece to
be cleaved, at about the center, and tilted slightly so that the blade contacts
the crystal at an edge as shown in
2-4. Tap the back of the razor blade
sharply with a small hammer, and the crystal will cleave into two pieces.
A little experience will soon indicate how hard to strike the razor. The two
pieces may be cleaved again along anyone of the three perpendicular cleavage
planes shown in Fig. 2-5 to obtain still smaller pieces. Each time it it cleaved,
the crystal should be divided into roughly equal pieces. The cleaved sections
produced can often be used without further polishing for many qualitative applica­
tions. If polishing is necessary or desirable, then Part II, described above,
should be followed.
Note: Only single crystal NaCl or KBr plates can be cleaved. Saw blanks which are often used in sealed and demountable cells will not cleave. 9/74 Page 3-1
EXPERIMENT 3 Determining the Thickness of a Sealed Cell and of a Polymer Film To determine the thickness of a sealed liquid cell and of a polymer
film by the interference fringe technique.
A sealed cell (thickness 0.015 to 0.3 rom) and the polystyrene calibra­
tion film.
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required
for quantitative
The value should be verified from ti:me to ti:me
since the thickness :may change due to a gradual erosion of the internal sur­
faces of the crystal windows in the celL In addition to the thickness of cells,
the thickness of polymer films 'is also important both for quantitative analysis
of the film and for a knowledge of the thickness, itself.
The basis for the measurement is the interference fringe pattern pro­
duced when the transmission of the film or empty cell is recorded over a
range of frequencies. This pattern, an effect of the wave nature of light, re­
sults from the interaction between radiation which is reflected by the inner
surfaces and then transmitted. Unless absorption occurs, most of the radia­
tion at any given wavelength is transmitted. A small amount, however, is
reflected and then transmitted as shown in Figure 3-1, a simplified sche:matic
diagram. The amount reflected depends on the difference in the refractive
indexes of the two materials at the reflecting interface.
The reflected radiation, as finally transmitted, may be exactly in
phase with the radiation not reflected, it may be exactly out of phase, or it
may be somewhere in between. If in phase, reinforcement occurs and the
cell (or film) transmission is maximum; if out of phase, destructive inter­
ference occurs and the transmission is minimutn. Between the maxima and
minima, the transmission changes gradually with frequency as radiation
which is neither entirely in phase nor entirely out of phase interacts. As the
spectrophoto:meter scans the cell or film transmission at one wavelength
after another, a wavy interference fringe pattern emerges such as that
shown in Figure 3-3 or Figure 3-4.
9/74
Page 3-2
/
A
c
B
-:": =-~~~ ::---- --
- - - ....
o
--­
~---------d--------~v.
-------REFLECTED
-------REFLECTED - - - - - TRANSMITTED
- - - - TRANSM ITTED Fig. 3-1 - Path of radiation between
the inner surfaces of a filITl or cell.
Path of reflected radiation is drawn
at an angle to separate it froITl that
transITlitted. Fig. 3-2 - Wave patterns for trans­
ITlitted and reflected portions of radia­
tion when cell thickness, d, is such
that 2d '" ITl"ll , the in-phase condition
for a fringe ITlaxilnuITl. The reflected
radiation, as finally transITlitted, is
in phase with that transITlitted directly.
The thickness, d, of a ce1l or filITl can be calculated from data obtained froITl the fringe J,lattern by using Equations land 2, below. Am
For c ells:
d =
For filITls:
d =
where:
2(vl-v2)
Am
2n(vl-v2)
Equation 1
Equation 2
d= thickness, in centimeters (em).
frequency at which first ITlaxiITlurn (or ITlinimum)
occurs, in wavenumber (em-I) units.
v2
=; frequency at which last maxhnurn (or minimum)
occurs, in wavenumber units .
.c.m number of complete fringe maxima (or minima) in the
interval from VI to v2, a whole number. One complete
fringe minimum is from point X to point Y in Fig. 3-3.
n = index of refraction for the filITl.
The use of these equations should become apparent when performing the Pro­ cedure which follows. These equations and their origin are discussed in more detail in the Discussion following the Procedure. 9/74
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0.015 to 0.3 ITlm), in
good condition, in the saITlple beam and obtain the spectrUIll from 4000 to
400 CITl- l . The spectrum produced should be slITlilar to that shown in Figure
3- 3 except for the spacing between ITliniITla or ITlaxima. The calculation, based
on Equation 1, is deITlonstrated on the figure with appropriate values of Am,
VI and vZ. Note that as many fringes as possible are counted in order to re­
duce the effect of errors in ITleasuring vl and vZ.
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the in­
strUIllent. Obtain a spectrUIll from 4000 to 400 ern-I. The curve should be
similar to that shown in Figure 3-4. The interference fringes used in the
calculation are noted on the curve. In this case, Equation Z should be used.
A refractive index value of 1. 6 was used for polystyrene. The operator should
be ahlp to verify that his polystyrene film is approximately the same thickness
as deterITlined in the exaITlple.
DISCUSSION
The phase relation beh';'een radiation translTIitted straight through a
cell (or film) and that reflected by the inner surfaces and then transITlitted
depends on several factors. In the case of the Model 735, where the rays of
incident radiation are perpendicular, on the average, to the cell (or film) sur­
faces, the phase relation depends on the cell or fillTI thickness, d, the radiation
FREQUEtoICY (CM')
4000
3600
3200
2800
2.400
2000
1800
1600
1400
1200
1000
800
Fig. 3-3 Fringe pattern obtained for an elTIpty O. 1 = thick sealed
KBr cell
9/74
600
400
Page 3-4
FREQUENCY (CM')
~ooo
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
..00
I
//11
I
Ii
_LJ-j-"H-+"-t+t-H-++--+"+++'~+t+++-tt-~t+il,m*,",: i r-t-HffI+IH+"H-H'+'f-IttI+f1-t-H-H+HH-+HI
~~-H-t.IHH+++I
j
j-:­
~
i
ji I i-I .6m=ll
.6m
- r~ ~.
1~1r:'-H-j
~
++ d = 2n(v1- v2)
II
!i
tlt+ttti'++-ttttti"++-t+-Irtt-rttf vl ...
::
Z
«tf~
27~cx:m~l,f, "I ,11
I! I III
_---..,.--'1"'1'-:-,----_,...,..,..,..,
:1
'-l+m-tH1+1+m-t-l-i-'--H-H d = 2 x 1.6(2700 - 2025)-H-t4+i-IH++h4-l
t: 1-++++i+++++++i++H+'-IIH-HI--++++++l-4+++'V2 =
~
I
I:'
I i I 2025cm- 1 '
t
ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++'-H-t+l+'C1'4¥1-t-m-ttit+l+H d = 0.005 Oem
-H-m-tH+H+-t-t
~
I
I1
Wti
-ttH+"rr,:,+rrm1 d = 0.05 Cbm
'i'
i
HH+!
I
I
f,
+
:1
,II HW'+I+,HH
1-++++i++H-f-~!+f+++~'-J!fl~H+}H+l-rt+++i-H~'~',-tHH+-H++lH'+I'++H-H~j+H'-H-t-H-t'H-f-j'-H-tHI-H-jjll
, 20 "
,i1'
r-t'+H+H+Ht.~t!lJr-t+r-tt-H
2,5
..
+
o
3,5
(MICRONS)
11
1213 I.
16
l' 20
25
Fig. 3-4 - Fringe pattern obtained with the 0.05 nun thick polysty­ rene calibration saITlple wavelength, A, and in the case of a filITl, the index of refraction, n. If the
phase relationship and wavelength are known, therefore, it is possible to de­
terITline the thicknes s of an eITlpty cell. If in addition, the index of refraction
for a filITl is known, then its thickness can also be found. Except for the in­
dex of refraction, all of this infoxITlation is available in the fringe pattern of
the cell or filITl transITlission. On the other hand, if the filITl thickness is
known froITl SOITle other ITleasureITlent, the refractive index ITlay be deterITlined.
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between
cell thickness and phase in a siITlplified fashion. Here, the cell thickness, d,
is =ade equal to one wavelength, or d = /... The reflected wave travels a dis­
tance 2d farther than the wave not reflected. If the distance 2d is equal to ITlA
(where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge
froITl the cell cavity in phase, and the fringe pattern will show a ITlaxiITlUITl; a
ITliniITlUITl will occur when 2d = (ITl + 1/2)"/1.. We now have a ITlatheITlatical rela­
tionship between cell thickness and wavelength which is related directly to the
fringe pattern. For any ITlaxiITluITl, the cell thicknes s is:
d = rnA
Equation 3
2
However, the fringe pattern does not give a value for ITl directly. It
does show the wavelengths at which various ITlaxiITla occur. Since the value
of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla), the following relations
can be established for two different ITlaxiITla in the fringe pattern:
9/74
Page 3-5
2d
m1 Al
(for maximum 1)
2d (for maximum 2)
2d
2d
ml-m2 = A2
"1
m2"2
Solving for d:
d
=
"1"2 (m 1 -m 2 )
2("r Al)
Am, then:
d
=
A1 A2 (.~m)
Equation 4
2(['2-1-1)
Note that in Equation 4, the quantity (A m) corresponds to the number of
maxima between wavelengths "1 and "2" For an empty cell, the value of
d depends only on the wavelengths at which the two chosen maxima occur and
the nUluber of maxima between them.
When the thickness of a film must be measured, the nmnber of waves
in the film depends on the index of refraction, n. This value must be obtained
from a handbook or other source. Equation 3 now becomes
d
= rnA
2n
and Equation 4 becomes:
Equation 5
Generally, Equations 4 and 5 will enable the user of the Model 735 to
determine the thickness of a cell or film. Both equations, however, are based
on the premise that the incident radiation is propagated in a direction perpendi­
cular to the film or cell surfaces (angle of incidence = 0 0 ), which is the normal
situation in the Model 735. If the angle of incidence, 1/), were not 0 0 , it would
be necessary to use the general equation for thickness, which is:
d
This reduces to Equation 5 when (/)
Equation 6
0°.
9/74
Page 3- 6
Throughout the discussion above, the calculation of cell or film thick­
ness is based on a unit of wavelength (in the infrared, the micron). It is more
convenient to make the calculation using wavenumber units when using the spectro­
photometer. For any given wavelength, the corresponding wavenumber is the
number of waves which will occur in one centimeter. If wavelength, II, is
given in microns, the usual unit for infrared radiation, then the corresponding
wavenumber is 10 4 /11 waves per centimeter (cm- l ).
Wben wavenumber units are used, Equations 1 through 6 must be modi­
fied. Equation 3 for cell thickness, based on n := 1, at a fringe maximum
becomes:
4
d == 10 m
2v
where d is in microns;
Equation 7
1£ d is in centimeters, then:
d = ..!!!...
2v
Equation 1 for cell thickness, based on n
1, becomes:
Equation 2 for film thickness, based on n " 1, becomes:
Equation 9
Equation 6 for film thickness, based on n I 1, and an angle of incidence (/) " 0,
becomes:
Equation 10
9/74
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate
the procedures used.
MATERIALS
Indene, carbon tetrachloride, carbon disulfide, mineral oil (such as
Nujol), perfluorohydrocarbon oil (such as Fluorolube), silicone grease,
demountable cell, O. 1 mm sealed cell or demountable sealed cell, two
NaCl or KBr windows for demountable cell, spacers for demountable
cell, eye droppers, 1 ml glass syringe, rubber "ear" syringe.
INTRODUCTION
Perhaps the simplest, most common method of sample preparation for
the infrared examination of liquids involves placing an undiluted sample between
a pair of transparent crystal windows. This sandwich is clamped together and
placed in the sample holder of the spectrophotometer, and then the spectrum is
obtained. This spectrum is one of the most characteristic physical properties
of the sample. No solvent or matrix interferences and interactions are pre­
sent to contribute to difficulties in interpretation and identification.
For a good infrared absorption spectrum, one which accurately pro­
vides the information needed, however, the analyst must take into account
the intrinsic intensities of the bands in the sample spectrum and also the ef­
feet of sample thickness on band intensity. The intensities of the absorption
bands of different materials can vary appreciably. For example, nonpolar
materials or compounds containing highly polar functions, such as the car­
bonyl group, are moderate to strong absorbers. Furthermore, the thicker
a sample (that is, the greater the number of molecules along the radiation
path which may interact with, and absorb, the incident radiation), the more
intense the absorption bands. Therefore, one should expect to use different
thicknesses for different samples to optimize the spectra obtained for the
information needed.
As a general rule, nonpolar materials require a sample thickness in
the vicinity of O. I mm. On the other hand, thicknesses in the range from 0.02
mm (or thinner) to 0.05 mm will be required for polar materials.
This experiment will familiarize the operator with the various techni­
ques for preparing samples of pure liquids.
9/74
4-2
PROCEDURE
Part I
Sealed Cell
Remove the two Teflon stoppers from
the O. 1 mm sealed cell and lay the cell on a
flat surface with a pencil under one end, as
shown in Figure 4- 1, to facilitate filling with­
out formation of bubbles. Draw about O. 5 ml
of carbon tetrachloride (WARNING: Carbon
tetrachloride is toxic) into the syringe and
insert the syringe into the lower fitting of
the cell. Slowly fill the cell by gently de­
pressing the plunger of the syringe. Do not
Fig. 4-1 - Correct way to
force the plunger of the syringe as this may
fill a sealed cell
put excessive hydraulic pressure on the cell
and force the cell open, break the amalgam
seal, and increase the cell thickness. Watch the liquid as it fills the clear open­
ing; it is advisable, whenever possible, to add 0.2 ml of sample in excess of
that needed to cover the opening. About 0.2 to 0.4 m1 should be required if
the cell is properly filled. Remove the syringe and
insert a Teflon plug,
with a twisting motion, into the' same fitting; then insert the second Teflon plug
in the same manner into the other fitting. If liquid fills the top port, remove
most of it with a
of tissue. If the port is left full when the second plug
is inserted excessive pressure may distort or rupture the cell.
Put a sheet of chart paper on the instrument without a cell in either cell
holder. Record an 10 baseline as described in Part I of the Procedure in Ex­
periment 1. Adjust the 1000/0 control to position the pen at 100% transmittance
FREQUENCY (CM ')
.4()00
3600
3200
2Il00
2400
2000
1800
1600
1.400
1200
1000
800
600
Fig. 4-2 - Carbon tetrachloride spectrum, O. 1 mm sealed cell
9/74
"00
Page 4- 3
FREQUENCY (CM')
4000
3600
3200
2800
2,(00
2000
1800
1600
1-'00
1200
1000
800
600
400
Fig. 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of
bubbles in sealed cell (0. 1 nun sealed cell)
on the chart, then place the cell in the sample position of the instrument and
record the carbon tetrachloride spectrum as described in Part II of the Pro­
cedure in Experiment 1. Remove the chart paper from the recorder and fill
in the appropriate information on the upper part of the chart.
The spectrum should resemble Figure 4-2. If the band near 770 crn­ l
has a transmission of more than 2. 50/0, examine the cell for bubbles. The
spectrum produced using a cell with bubbles is shown in Figure 4- 3. Compare
this spectrum with Figure 4- 2. Note that the absorption bands in Figure 4- 3
are less intense, i. e. they transmit more of
the radiation. This is because the instrument
"sees" partly sample and partly air, and air
transmits more radiation than the sample.
Rerun the spectrum if necessary.
Remove the sealed cell from the spectro­
photometer and remove the Teflon plugs from
the cell. With the glass syringe, withdraw the
carbon tetrachloride from the cell, then empty
the syringe. With the rubber syringe, blow air
first through the cell until the cell is dry. then
through the glass syringe until it is dry. Now,
lay the cell down once again, with one end
slightly raised, ready for filling. (A push-pull
technique using two syringes should be used to
clean and dry cells less than 0.075 mm thick.
One syringe is used to contain the solvent and the
other to generate a vacuum which pul1s the solvent
through the cell (Fig. 4-4). This technique
9/74
Fig. 4-4 - Use of two
syringes to clean cells
less than 0.075 mm thick
4-4
4000
3600
3200
Fig. 4-5
2800
2400
FREQUENCY (CM')
1800
1600
2000
1400
1200
1000
800
600
Carbon disulfide spectrurrl, 0.1 rrlrrl sealed cell
is also often useful for filling thin cells.)
Use the 1 rrl1 syringe to inject about 0.4 rrl1 of carbon disulfide into
the cell.
CAUTION: Carbon disulfide is
toxic, extrerrlely volatile, and
very flarrlmab1e. Handle it
under a hood, with no open
flarrles or hot plates nearby,
where the fumes could contact
therrl.
..
=.
-~=",,:::tl,
!Oiiii
.....
. .___
~;;;;.
=.==.~
NEOPRENE
GASKET
=:::::r==:::r='='===:J.I....'---WINDOW
__....-==-..__
~~------SPACER
~WINDOW
~
.. ~" .
NEOPRENE
GASKET
~
BACK PLATE
4- 6 - Derrlountable cell
as serrlbly diagrarrl
9/74
Replace the Teflon plugs firrrlly
(with a twisting motion), first in
the lower fitting and then in the
upper
Place the cell in
the instrument sample position
and obtain a spectrum. The spec­
trUrrl produced should resemble
tha t in Figure 4- 5.
Carbon disulfide and car­
bon tetrachloride are two of the
rrlost common infrared solvents,
and they are generally used in
conjunction to cover the spectral
range of the Model 735. Carbon
tetrachloride may be used from
4000 cm- 1 to 1230 cm-i, while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i. Keep the spectra
obtained for these materials in a permanent file; they will be used in Experi­
ment 5 and may be useful as part of a general reference file.
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the
studs of the cell upwards as shown in Figure 4-6. Lay one of the rubber gas­
kets on the cell back plate with the aperture in the gasket centered on the
aperture in the back plate. Now place one of the rectangular KBr windows on
the rubber gasket. (Handle the windows at their edges; hands should be
dry or finger cots should be used.) Lay a 0.025 mm spacer on the window.
(If the spacer is wrinkled, place the second KBr window on it and press the
window firmly to smooth out the spacer. Remove the second window.) With
an eye dropper, put two drops of indene on the lower window, in the aperture
of the spacer. Place the second window on top of the spacer by bringing one
end of the window into contact with the spacer first, and then lowering the
other end. If the top window is lowered properly, the indene will fill the
opening in the spacer and no bubbles will appear. Center the second rubber
gasket on top of the windows, place the front plate over the studs, and firmly
and evenly tighten the four nuts·. Excessive or uneven tightening of the four
nuts may crack the windows. Obtain the spectrum as described in Part 1.
The positions of the bands noted in Figure 4-7 may be used for cbecking the
frequency calibration of the instrument.
Part III
Demountable Cell - without Spacer
Begin as in Part lI, but do not place a spacer on the surface of the
lower window. With an eye dropper, place two drops of mineral oil (Nujol)
on the surface of the window near the center. Place the second window and
rubber gasket on top. If necessary use the top window to spread the oil on
the bottom plate so there are no air spaces or bubbles. CialDp the windows in
place with the top plate and thumb nuts. A sample pr epared in this manner,
as a very thin film, is often called a capillary filnl.
Obta.in the spectrum as described in Part I, and refer to Figure 4- 8.
Save the spectrum for reference in Experiment 6, which describes the use
of mineral oil as a medium for obtaining the spectra of solid powders.
Mineral oil can be removed from the cell windows by wiping them with
tis sue and rinsing off the residue with chloroform.
.
011
Follo,,: the. same procedure to obtain a spectrum of perfluorohydrocarbon
as shown m Flg. 4-9.
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II, but do not place a spacer on the lower window.
Put a small amount of silicone grease on the lower window and with the
second window. smear the grease and press it into a thin
Put the
9/74
film.
Page 4-6
FREQUeNCY (CM'l
4000
3600
3200
2900
2400
2000
S
~.O
1900
1600
1400
1200
1000
800
600
400 {MICltONSl
Fig. 4-7 - Indene spectrunl. 0.05
== denlountable cell
FReQUENCY (CM<')
4000
3600
3200
2800
I
2000
1800
I
,.
"
2./00
1400
1200
1000
BOO
600
400 I
,
"
1600
"""""'$I
10
11
12
131.t
J6
'b20
25
Fig. 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell
FREQUENCY (CM')
4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
400 Fig. 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in
demountable cell
9/74
Page 4-7
FREQUENCY (CM') ,,000
3600
3200
2800
2000
1800
1600
1<100
1200
1000
800 Fig. 4-10 Spectrum of silicone grease smear run in demountable
cell
second rubber gasket on the top window and clamp the windows firmly with
the top plate and thumb nuts.
Obtain the spectrum as described in Part 1. It should be similar to
that shown in Figure 4-10. If so, keep it for future reference. If the absorp­
tion bands are too strongly absorbing, either tighten the thumb screws fur­
ther, to thin the sample, or disassemble the cell, wipe one window clean, and
then reassemble the cell. (Be sure to tighten the thumb screws evenly to avoid
cracking the windows.) Again, obtain the spectrum and compare it with
Figure 4-10.
Silicone grease is a common impurity in many samples, since it is
often used as a lubricant.
The cell windows can be cleaned of silicone grease by wiping them with
a piece of tissue moistened with toluene. Afterwards, rinse them with petrol­
eum ether or toluene.
9/74
Page 5-1
EXPERIMENT
5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate
the effect of solvent absorption bands.
MATERIALS
Carbon tetrachloride, carbon disulfide, toluene, polystyrene, xylene,
three 10 ml volumetric flasks, three 1 ml syringes, demountable cell with
NaCl or KEr windows and 0.025 rom spacers, two 0.1 mm sealed cells (or demount­
able sealed cells with 0.1 rom spacer), rubber "ear" syringe.
INTRODUCTION
Often, the analyst will find it necessary to analyze samples in solu­
tion. The samples may be received in solution or may have to be put into
solution if the absorption bands of the pure materials are so exceptionally
strong that their true shapes cannot be discerned however thin the pure sample.
The spectra of samples in solution present problems not encountered
with pure samples. All heteronuclear molecules, which include any solvent
one might choose, have an infrared spectrum. In solutions, the spectrum of
the solvent adds to that of the sample and may interfere with observation of
the sample bands. In selecting a solvent, therefore, it is essential to know
the characteristics of its spectrum. The purpose of this experiment is to ac­
quaint the operator with some of the common infrared solvents, especially
carbon tetrachloride and carbon disulfide, which are most often used.
There are at least three methods for overcoming, in part, the effects
of interfering solvent absorption bands:
1.
Obtain the spectrum of the pure sample as a capillary film or in a thin
(0.025 mm path length) sealed or demountable cell.
2. Change the solvent to one with bands that do not interfere with the sample
bands. Since all solvents have several absorption bands in the infrared,
it is generally not possible to obtain a complete spectrum free from inter­
fering solvent bands. The normal procedure is to use two or more sol­
vents to cover the complete range. If one compares the spectra of CC14
and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3), one finds that in
those regions where CCl4 interferes, CSZ does not. The converse is also
true.
9/74 Page 5-2
3. Obtain a compensated spectrUIll of the sample by taking advantage of the
optical null balancing syste:m of the instrUIllent; that is, place a cell con­
taining pure solvent in the reference beam of the spectrophotometer. When
the spectrUIll of the solution is run, the instrUIllent will then automatically
compensate for the solvent absorption bands. For the Perkin-Elmer Models
7XX, X67, and X21, this technique is successful only in those regions where
the solvent transmits more than 20%.
It is important, when obtaining compensated spectra, to bear in mind this
requirement for no less than 20% transmittance anywhere in the solvent
spectrum and to understand the reason for it. For proper operation, an
optical null instrUIllent such as the Model 735 requires that a certain
amount of radiant energy reach its detector. When this minimum energy
requirement is not satisfied, the pen system will be sluggish and will not
accurately follow the absorption behavior of the sample.
A si:mple experiment with three opaque cards will demonstrate the effect
of low energy. With a white card, partially block the sample beam of the
instrument to make the pen indicate 15"l0. (Think of this as a solvent ab­
sorption band that allows only 150/0 transmittance.) Holding the first card
in position with masking tape, use a second card to partially block the
reference beam, to bring the pen back up to about 95%. Tape this card
in place, also. (Think of this second card as the compensating solvent,
which eli:minates the effects of the solvent in the sample solution.) Now,
totally block the sample beam with a third card to simulate an absorbing
sample, and observe the pen behavior. It will appear to move sluggishly,
and will go downscale rather slowly; it will not be able to respond accur­
ately to rapid changes in light transmission like those encountered when
scanning a sample spectrUIll. In the above experiment, if a very strong
solvent band were simulated by completely blocking both beams with the
cards, thus allowing no energy through either bea:m, blocking the sample
beam with a third card would not affect the pen position. Under such con­
ditions, the recording system is said to be "dead. If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20% by volUIlle solutions of toluene in carbon tetrachloride and
toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of
toluene to each flask with a glass syringe and diluting to the mark with carbon
tetrachloride and carbon disulfide, respectively.
9/74
Page 5- 3
Fill the O. I mm sealed cell with the carbon tetrachloride solution as
described in Experiment 4, and obtain the spectrum. Compare this spectrum
with that of carbon tetrachloride obtained in Experiment 4 and with the spec­
trum of pure toluene shown in Figure 5-1. Note those spectral regions where
the carbon tetrachloride absorption bands interfere.
Leave the first cell in the sample beam and fill a second O. 1 rom sealed
cell with carbon tetrachloride. Put it in the reference beam of the instrument
and run a spectrum. The instrument will automatically compensate for solvent
absorption. Again, compare the spectrum with Figure 5-1. Note that there
are regions in the compensated spectrum where either absorption bands have
not been recorded or where the accuracy of the recorded band intensity and
frequency is reduced. Comparison with Figure 4- 2, will show that these re­
gions correspond to the locations of the strong (less than 20% transmittance)
solvent absorption bands.
Remove both cells from the instrument and draw out the contents with
a glass syringe. Flush the cells with CC14 using the syringe, and dry them
by blowing air through them with the rubber syringe.
Fill one of the cells with the CSZ solution and obtain the spectrum.
Compare this spectrum with that of CSZ obtained in Experiment 4 and with the
spectrum of pure toluene shown in Figure 5-1. Note the regions where the
CSZ absorption bands interfere with observation of the toluene absorption bands.
Now, run a compensated spectrum as described above for the CC14
solution. Clean the cells and syringes.
FREQUENCY (CM') 4000
3600
3200
2800
2400
2000
1600
1600
1400
1200
1000
600
Fig. 5-1 - Spectrum of pure toluene run in 0.02,5 mm sealed cell
9/74
600
400 Page 5-4
FREQUENCY (CM')
4000
3600
3200
2800
2400
"
2000
1800
(MICRONS)
1600
1400
1200
800
1000
10
11
600
400
12
Fig. 5-2
Spectrum of 20% weight-to-volurne polystyrene in
xylene run in a 0.025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene
in a 10 ml volumetric flask and diluting to the mark with xylene. Retain
the solution for use in Experiment 8.
Set up a demountable cell with a 0.025 mm spacer as described in
Experiment 4. With a dropper, place 2 drops of the polysytrene solution on
the window in the center of the spacer opening. Place the second window on
top of the spacer, avoiding bubbles, and clamp with the top plate and four
thumb nuts. Obtain a spectrum, compare it with Figure 5-2, and retain it
for comparison with that prepared in Experiment 8.
Disassemble the cell. Carefully clean the crystal windows and spacer
by rinsing them with xylene and drying them with air.
Reassemble the demountable cell with xylene as the sample. Obtain
the spectrum and compare it with the spectrum of polystyrene solution ob­
tained previously. Note and mark those bands which do not belong to the
xylene solvent and, hence, do belong to the polystyrene. Clean the cell.
9/74
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in per£luorohydrocarbon. MATERIALS
A 50 mm or 65 mm (o. D.) mullite or agate mortar and pestle,
(Perkin-Elmer part no. 990-4906) mineral oil such as Nujol, (Perkin-Elmer
part no. 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer
part no. 186-2301) or perchlorokerosene, demountable cell with two KBr windows,
rubber policeman, 2, 4-dinitrophenylhydrazine, phthalic anhydride, talc (baby
powder), sodium bicarbonate.
INTRODUCTION
One of the most generally useful techniques for preparing a solid sam­ ple for infrared analysis is mulling. Good results are obtained by this method only if the average particle size of the solid is somewhat less than the wave­ length of light the particles are to transmit, or if the medium used to suspend the particles has nearly the same refractive index as the sample. Since the latter is rarely (if ever) true, one generally must reduce the average particle size of the sample to 1 or 2 microns. If the sample particles are of this size when received, or if the sample is quite frangible, it may be placed directly on a crystal window, a drop or two of mulling agent added, and a second win­ dow placed on top. A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly. On the other hand, coarse or hard particles will require some grinding. The most common mulling agent is mineral oil, which for many spectra can be used over the full wavelength range of the instrument. How­ ever, it may be desirable in some cases to use a per£luorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l , and mineral oil from 1380 cm- l to 650 cm- l . See Experiment 4 for reference spectra of the two mulling agents,
Fig. 4-8 and Fig. 4-9.
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination. 9/74
Page 6-2
FREQUENCY (CM' I
4000
3600
3200
2800
2400
2000
I·"
T'
-.
T
....
~
[
I
" .
I
'
"
.~....!
.~
~.
I
•
!
!
~
1200
i
I
I
i
I
!
•
!
I'.'
I·~:·
600
400
I:
i!:
I
Ii
!
L
Ii !i
:"
0 1 ;:;,
]·T·~-
"
1;, l'..
40
20 I
I
'11 I : I!
II
800
.L~, "i.I
, .
' • lL;.~
~
•..
....
-l •
1\
.~
!
1000
!V\
I
.1
41
"
...
...
I
~J
1400
.•.
T, ~n
,
..
1600
'~':,~I;i.~:;~
•
, '
II I
.....
1800
.1
1\
~
\J
II
' !I
\
\
10
11
12131"
16
1820
25
Fig. 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window. Add one sITlall
drop of ITlineral oil, and place the second window on top, without a spacer.
With a gentle circular and back-and-forth rubbing motion of the two windows,
evenly distribute the ITlixture between the windows. The mixture should ap­
pear slightly translucent, with no bubbles, when properly prepared. Cla=p
the sandwich between the front and back plates of the deITlountable cell, as
described in Experiment 4, and obtain a spectrUITl. Ideally, the strongest
absorption band should have a transITlis sion of 0 to 10% and should not be
totally absorbing for more than 20 cm- 1. The spectTUITl obtained should re­
seITlble that shown in
6-1. If the bands are distorted, as shown sche­
matically in Figure 6- 2, the particle size is too great and some of the radia­
tion incident on the ITlull has been scattered out of the saITlp1e beam. This ef­
fect, called Christiansen scattering, indicates that the particle size must be
reduced if a better spectrUITl is required. Determine the bands due to the
mineral oil froITl the spectrUITl of Nujol in Fig. 4-8.
Talc produces a very strong absorption spectrUITl and must be care­
fully cleaned from the cell windows to prevent contaITlmation of future samples.
Wipe the windows with a tissue, then wash them several times with methylene
chloride. Run a spectrum of the cleaned windows to be sure they are clean.
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 2.5
(4000 em-I), the short wavelength limit of the Model 735. is most important when
9/74
~
Page 6-3
preparing a mull. Proper preparation
requires patience, diligence, and effort.
There are two techniques for
grinding: dry grinding and wet grinding.
The former, which applies to compounds
known to be relatively stable, will be
described here; the latter, which applies
to those materials which may lose water
or undergo crystalline modification, will
be described in Experiment 7, Prepara­
tion of KBr Discs. Both techniques can
be used to prepare either mulls or KBr
discs, depending to a great extent on
the sample.
UJ
<.>
Z
~
...
'iii
.'"
...
:z
0:
WAVELENGTH (MICRONS I
Fig. 6-2 - Typical band distortion resulting from Christiansen
The sample chosen here,
2,4-dinitrophenylhydrazine, is parti­
scattering. Dotted line repre­
sents normal band shape
cularly difficult, and if one succeeds
in preparing a good mull (and, as a
result, a good spectrum) with it, he should feel assured he has the technique
well in hand. As an alternative, phthalic anhydride is somewhat easier to
handle. The mulling procedure for both materials is the same.
Place an estimated 10 to 15 mg of 2, 4-dinitrophenylhydrazine (or
phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar. Larger
amounts of sample are more difficult to grind. Break up the solid and dis­
tribute it over the surface of the mortar by light grinding with the pestle.
Now, with a vigorous, hard, back-and-forth motion of the pestle, grind the
sample until it becomes firmly caked on the sides of the mortar and quite
glossy in appearance. This process may take from 2 to 10 minutes depending
on the sample and the operator.
When the caked. glossy condition has been reached. add a small drop
of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to
1350 cm- l region, or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the
mortar. Grind the saIrlple with a vigorous rotary motion until all the material
is suspended in the mulling agent. It Irlay be necessary to add an additional
sIrlall drop of the Irlulling agent as this grinding is continued. The ideal con­
sistency of the final mixture is about that of Vaseline
®.
Remove the mull from the mortar with a clean rubber policeman (these
are often coated with talc and should be wetted with alcohol and wiped in order
to clean them), and transfer it to a KBr plate. Place a second window on top
of the first and distribute the saIrlple evenly between the plates. The mull
should appear slightly translucent if properly prepared.
·9/74
Page 6-4
FREQUENCY (eM 'j
4000
3600
3200
2800
2400
I
2000
,
I
1800
1600
1400
1200
1000
800
600
400
600
400
Fig. 6-3 - Spectrum of 2, 4-dinitrophenylhydrazine mull
FREQUENCY (CM~)
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3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
Fig. 6-4 - Spectrum of 2, 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering Clamp the sandwich in a demountable cell in the normal fashion and ob­
tain a spectrum over the spectral range appropriate to the mulling agent.
The resulting spectrum should be similar to that given in Figure 6- 3.
1£ the absorption bands appear too strong, the mull may be thinned somewhat
by tightening the locking nuts on the demountable cell. Figure 6-4 shows band
distortions which are characteristic of the Christiansen scattering effect. If
such distortions are observed in the spectrum obtained, then the grinding pro­
cess has not been mastered and should be repeated from the beginning with the
dry material.
9/74
Page 6-5
FREQUENCY (CM·')
4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
10
(MICRONS)
800
1000
II
121314
600
400
16
Fig. 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM')
.000
3600
3200
2800
2400
2000
1800
1600
(MICRONS)
1400
1200
1000
10
11
800
600
12
16
13 I"
400
18
2()
2S
Fig. 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in
perfluorohydrocarbon and in mineral oil, respectively.
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II, but with a sample of sodium
bicarbonate. A spectrum similar to that shown in Figure 6-7 should be ob­
tained. If band distortion occurs, repeat the grinding of the dry material un­
til a satisfactory spectrum is produced.
9/74
Page 6-6
I
4000
3000
3200
2800
2.0100
2000
FREQUENCY (CM')
1800
1600
1400
1200
1000
800
Fig. 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
9/74
600
<100
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc. MATERIALS
A 50 mm or 65 mm (0. D) mullite or agate mortar and pestle (990-4906); infrared quality 100 to 200 mesh KBr powder* (990-5927); reagent grade ethanol; toluidine red or phthalocyanine green pigment, or benzoic acid (Sample I); small piece of quartz or granite (Sample II); 13 mm KBr die; 13 mm KBr disc holder; eye droppers; balance capable of weighing I mg with good precision; micro spatula; vacuum system capable of providing 1 to 2 rnm vacuum; 12 ton laboratory press; small camel's-hair brush; tweezers. INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force
into clear discs having high transmission throughout the 4000 to 400 cm- l range
of the infrared instrument. Before pressing, samples may be mixed with the
KBr powder at a sample concentration level of O. 1% to 20/0, and their spectra
obtained in the KBr matrix. As in the mulling technique, the sample must be
very finely ground in order to reduce scattering losses and absorption band dis­
tortions. This experiment demonstrates a wet-grinding method which has been
found particularly effective for reducing the particle size of inorganic mater­
ials as well as some organic compounds. As with the mulling technique, the
choice of wet or dry grinding depends on the sample and the quality of the
spectrum desired by the operator.
A word of caution concerning the KBr technique is required. Modifica­ tions in the spectra of some samples may occur due to ion exchange with the KBr matrix, pressure effects, or transformations to other crystalline forms. This does not detract from the general usefulness of the technique, but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques. 'PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base.
(Consult the instructions for the
*Dry the KBr powder in an oven at 105 0 for 12 hours and store it in a desiccator.
9/74
Page 7-2
FREQUENCY (eM')
4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
.0100
Fig. 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a
disc.) Insert the small, lower ram into the die opening with the shiny surface
up. Completely transfer 300 ~5 mg of infrared quality KBr powder to the die
opening. (Use the
of a carriel's-hair brush to brush the KBr powder from
its container.) Insert the top plunger, and with a light rotary motion of the
plunger, level the sample. Connect the die to the vacumn system and evacuate
the die to a pressure of I to 2 r:rirn. of Hg for about 2 minutes to remove lightly
held water from the surface of the KBr and to remove air from between the
KBr particles. With the vacumn still connected, place the die on the press
with the top platen, if required, on top of the ram. Press for 3-4 m.inutes
at 10 to 12 tons of total force. Disconnect the die from the vacumn line, re­
lieve the pressure on the press, and remove the die. Invert the die and rem.ove
the base. Place the inverted die back in the press and center the split ring
on the die so that the lower plunger will be visible when forced from the die.
Now, with the press. force the plunger upward until the lower ram and disc
just clear the body of the die. Remove the die from. the press, and with the
tweezers, place the disc, which should be homogeneous in appearance, in the
disc holder. Insert the disc holder in the instrmnent and obtain the spectrmn
in the usual manner. The spectrmn should resemble that shown in Figure 7-1.
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the
mullite or agate mortar. With the eye dropper, add 10 to 15 drops of ethanol
to the mortar. Grind the sample with a vigorous, firm, rotary motion, re­
stricting the sample as much as possible to about 1/3 to 1/2 of the mortar
surface until the ethanol evaporates completely. Do not continue grinding
after the sample becomes dry. If samples are particularly hard, the wet
grinding step may be repeated.
9/74
Page 7-3
FREQUENCY (CM')
3200
4000
2800
2400
2000
!!IOO
1600
1400
1200
1000
400
800
,.,
Fig. 7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM')
4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
400
Fig. 7-3 - Spectrum of benzoic acid in potas sium bromide disc
showing band distortions caused by poor grinding
FREQUENCY (CM')
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3600
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2400
2000
1800
1600
1400
1200
1000
800
Fig. 7-4 - Spectrum of quartz in potassium bromide disc
9/74
400
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro
spatula and weigh out 1 ITlg (l/2
3/4 mg for toluidine red) on an appropriate
balance.';' Place the weighed, ground sample in a clean ITlortar. Weigh 300
!S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the sam­
ple. Use the pestle to mix the KBr and sample with a gentle rubbing motion.
Do not grind the KBr during the ITlixing procedure since reduction in particle
size is not required and will lead to adsorption of water on the KBr. Now add
15 ITlg of KBr powder and mix as before. Add another amount of KBr approxi­
ITlately equal to the total quantity in the mortar (1. e., add about 30 ITlg) and
mix. Continue adding and ITlixing KBr in this manner until all the KBr is in
the mortar. If this procedure is followed, a homogeneous mixture of the sam­
ple and KBr, with little water pickup on the KBr, will result. If the sample is
stable when heated, the mixture may be dried in an oven or vacuum oven for
1 hour at 105 to 110 0 C.
Completely transfer the mixture from the mortar to the die using the
side of the camel's-hair brush and press the disc as described in Part I.
Remove the disc froITl the die, ITlount it in the KBr disc holder, and obtain
the spectrum. It should resemble that shown in Figure 7- 2. If it exhibits
the band distortions evident in Figure 7 - 3, then the grinding was not done pro­
perly and a new saITlple ITlust be ground and incorporated into a new KBr disc.
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described
above. Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple, press it
as described, and obtain the spectruITl. The spectrum should be siITlilar to
that shown in Figure 7-4 and should not exhibit distortion due to the scattering
effect of large particles. Quartz is a relatively hard sample to grind, and the
10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is
prepared.
*For quantitative analysis, an electronic ultramicrobalance such as
®
the Perkin-Elmer Autobalance
could be used. If a microbalance is not available, it may be desirable to weigh out 3 mg of sample, mix it with 1 gram of KBr, and then take a 300 mg aliquot for pre­ paration of the KBr disc. 9/74
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution
in a volatile solvent.
MATERIALS
KBr
The polystyrene solution used in Experiment 5, demountable cell,
windows for the demountable cell, eye dropper, hot plate, paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses, parti­
cularly in quantitative work, but in some cases they suffer from the disadvan­
tages of overlapping and interfering solvent absorptions. In situations where
the analyst can choose the solvent used, these disadvantages can be largely
overcome, as when CSZ and CC14 are used in conjunction to cover the full range
of the instrument. At times, however, it is not possible to select the solvent
in which the solid of interest occurs and the analyst must accept the solution
as received. Typical example·s are samples of solvent- based paint or varnish.
Where possible, therefore, it is desirable to remove the solvent interferences
and to obtain a spectrum of the solute, only. This experiment describes the
procedures for preparing pure solid samples from solutions containing vola­
tile solvents.
PROCEDURE
Part I
Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to
the touch, but not hot. The KBr windows may crack if the hot plate is set at
too high a temperature. Place a paper towel on the hot plate and a KBr win­
dow on the toweL With the dropper, add two to three drops of the polystyrene
solution to the surface of the window while it is still cool. Allow the solution
to spread over the face of the crystal and evaporate completely. Some Inater­
ials retain solvent rather tenaciously and the analyst should allow several
Ininutes for complete evaporation of the solvent. The objective in this pro­
cedure is to obtain a fi1In having a thickness in the range of 0.03 to 0.07 rnm.
When the £i1In appears to be free of solvent, place the window in a
demountable cell; add a second window, if necessary, to claInp the first firInly,
and obtain the spectrum. The resulting spectrum should be siInilar to that
shown in Figure 8-1. Compare this spectrum with the solution spectrum
9/74
Page 8-2
FREQUENCY (eM·')
..000
3600
3200
2800
2400
2000
1800
1600
1400
1200
800
1000
10
11
12
13 1<1
600
16
18 20
D
Fig. 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5. If the bands produced by the film are appreciably
stronger than those in Figure 8-1, too much solution was used and the prepara­
tion must be repeated; if the bands are too weak, more solution should be
evaporated on the crystal. Examine the spectr= critically for solvent ab­
sorption bands. Consult the spectrum obtained in Experiment 5, Part II, for
the positions of the strong solvent bands.
9/74
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared
spec troscopy.
MATERIALS
Sealed cells (0.015 and 0.025 mm), hypodermic syringes, graph paper,
isopropyl alcohol, toluene, and methyl ethyl ketone.
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectro­
photometer is directly related to the strength of an absorption band (or the
absorbance at any given frequency) in the infrared spectrum of the sample.
The relation is expressed mathematically, in terms of sample concentra­
tion and radiation path length through the sample, by the Beer-Lambert
Law. Depending on the units of measurement, this law may be expressed
in a variety of ways:
Absorbance = A =
Where A
eel
mol. wt.
§.bc=log
I = log
1
T
100
log %T
= absorbance, observed from the spectrum (Figures 9-1 and 9-2).
e
=molar absorptivity or molar extinction coefficient.
c
= concentration in grams per liter.
l=b
= sample path length in cm (inside cell thickness).
a
= absorptivity, characteristic of the compound for that particular
absorption. ~ = e/mol. wt.
It is a
characteristic of the sample at a particular frequency,
It is often nearly the same for a group of compounds if the
absorption band is characteristic of that group.
= intensity of incident radiation (Figures 9-1 and 9-2),
9/74
Page 9-2
...0,2 A
Ii
I
;:!
£03
.~O.4
0,5
0,6
0,7
~.~
2.ll~ddd,kbl.I.d.d'=i=l=b.b.b.6.
FREOUENCY_
Fig. 9-1 - Absorption band recorded on a linear transmittance
scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t
'"'- 60
t:
::~50pt+III++1+~-t-~
~'OK+III++1++-t-t-+1"
«
~30
20
10
A'LOGt'LOG~'LOG~'LOG 6.06~O,~8
OLL~~~
__~~~~~~~~~
FREQUENCY_
Fig. 9-2 - A second example of an absorption band recorded on a
linear transmittance scale and on a nonlinear absorbance
scale
I
= intensity of transmitted radiation (Figures 9-1 and 9-2).
T
=t ransmittance =1/1 0 ,
or the ratio of the radiant
energy transmitted to the radiant energy incident
on the sample.
Most infrared spectrophotometers record the spectrum linearly in
transmittance units and nonlinearly in absorbance units. In order
9/74
Page 9-3
to relate such spectra directly to concentration, the transmittance
measurements must be converted to absorbance units. This can be
done either by (l) mathematical conversion; (2) using chart paper
having a nonlinear absorbance scale, as in the second parts of Figures
9-1 and 9-2; or (3) using a special ruler calibrated in absorbance
units, which has the same length as the transmittance scale on the
chart paper.
Usually for quantitative analysis by infrared spectroscopy the ab­
sorptivity, a or e, is not calculated. Instead, a standard is pre­
pared whichcontains a known concentration, C s ' of the .compound
in the unknown. The absorbance, As. of the standard is measured
at the same frequency that is used to measure the absorbance of
the unknown, A. The concentration of the unknown, Cu' in a binary
mixture can theVt be calculated from a simple proportion as follows:
A
a C 1
C 1
u
-
uu
uu
s
-
s s
s s
T=aCl =Cl
If the same cell or cells of exactly the same path length are used to
obtain the spectra of the standard and unknown, then the proportion
becomes AulAs = Cu/C s ' The concentration of the unknown can then
be determined from the expression C u = C s AulAs.
This equation demonstrates that the Beer-Lambert Law allows the
use of any units of concentration, such as percent by volume, per­
cent by weight, or mole fraction so long as the units used in the
calculations and determinations are the same as those used in the
calibrations. Moles per liter or grams per liter need only be used
when either e, the molar extinction coefficient, or
the absorptivity,
is used.
Often a graph of absorbance versus concentration is plotted (see Figures
9-12 and 9-13), particularly if the unknowns are expected to fall into
a wide concentration range or if the analysis is to be repeated but the
standardization is not. Determining the concentration of the unknown
then becomes a simple matter of measuring the absorbance at the fre­
quency used in preparing the graph and reading the corresponding con­
centration from the graph. A linear plot may also be obtained by
plotting transmittance. T-I/Io. versus concentration on semilog
paper (see Figure 9-14).
It is sometimes difficult to determine the value 'of transmittance (1 0 )
or absorbance (A2) at the base of an absorption band because of the
close proximity, or actual overlap, of other bands. For best pre­
cision it is preferable to use a horizontal baseline as shown for
bands a, band c in Figure 9-3.
9/74
Page 9-4
Fig. 9-3 - 10 for complex absorption bands. Dotted lines showexten­
sion of bands in an assumed symmetrical Lorentzian shape.
When a point is selected for determining the value of I or AI, it is pref­
erable that it fall between 20%, and 850/0 transmittance (0.7 and 0.1 absorb­
ance units). Also, even though such a point is not always taken at an ab­
sorption maximum (transmittance minimum) in quantitative analysis, it
is best to use an absorption maximum because it is easily located and
the spectrophotometer servo system is in equilibrium at that point.
In any but the crudest quantitative analysis it is necessary to determine
%T (or A, the band absorbance) for all samples (unknowns and standards)
from several spectra. A good procedure is to start with two spectra for
each sample. If the values determined for 'roT differ by more than 10/0, obtain
another spectrum. If the three values for %T vary by more than 20/0. make
still another determination from a fourth spectrum. The %T value to be
used is the average of all the determinations made.
Prepare the absorbance vs. concentration (calibration) curves using
the same instrument that will be used to analyze the unknowns. Use
the same cell and instrument operating conditions for the standard
and unknown solutions. If this is inconvenient, use fixed thickness
cells (Experiment 4) of accurately determined dimensions (Ex­
periment 3) and make corrections for any difference in thickness be­
tween the cell used for the standard solutions and the cell used for the
unknown solutions. Errors from the distortion or rupture of cells due
to improper cell handling techniques are very Significant in quantitative
9/74
Page 9-5
analysis.
Use care when filling and cleaning cells (see pages 4-2 and 4-3).
The following data show how a solution can be quantitatively analyzed.
The specific example is a ternary solution of toluene, isopropyl alcohol,
and methyl ethyl ketone which is widely used in the paint and adhesives
industries.
Figures 9-4, 9-5 and 9-6 are spectra of toluene, isopropyl alcohol and
methyl ethyl ketone, respectively. Figures 9-7 through 9-11 are spectra
of solutions of these three liquids at various concentrations (expressed
in percent by volume). The absorption band at 817 cm- 1 is conveniently
used for all calibrations and determinations of isopropyl alcohol and
the absorption at 695 cm- 1 is used for toluene. The methyl ethyl
ketone is determined by difference.
fREQUENCY (CM'! 4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
..•
1000
10
800
n
600 121314161120
25
Fig. 9-4 Spectrum of neat toluene in a 0.015 mm KBr cell
FREQUENCY (CM')
4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
800
1000
10
11
12
t~I"
Fig. 9-5 Spectrum of neat 2-isopropyl alcohol in a O. 015mm
KBr cell
9/74
600
..
1120
2S
Page 9-6
FREQUENCY (CM')
4000
3600
3200
2800
;-I -I; ~Hlj
!f
1800
2000
2400
1600
I
w
1200
1000
600
800
400
rtH- i
T
+Hltttifl\H~ctfH+++t'++ttffi-t++l+htttF·J
~
1400
I ,
!
U
I
I
'f
T
'f, .~.-
i i~
I
1+
!
,J
!l!(
"~
t.
ii •
"
Ii~
:1f'l\
J ~
!
~ i i ! ' i 1i
:
j
z
«
~
,
j
,"--
~
'"
H
"i
il I! I~
,!
i
I-­
;l t­
11
it
2
,
i:
l'
1NJl1
I
I
m
fMl
,
i
j ~i
'.
Ii' 1\
0
;:-f: Ii:
iii!
"
I:!I
i :.
II
" hit,.
"
i
'i I
ill
! '
Iii' 1,'1
n
"
.
"
!,
:'
~ -II: :
Ii 11+:
ji,fl'l
i: il!;
r'
(MOONS)
I,
.',
t::-
,.
~ ~--l
I : .i­
il i ,~+ ,1: I
LI
2.
" "
"
Fig. 9-6 - Spectrum of neat methyl ethyl ketone in a 0.015 mm KBr cell FREQUENCY (CM')
4000
3600
3200
~
2800
2400
2000
1800
1600
1400
1200
H+++1It+tttHHtti+ttttt+;+++++ttHttl.f-oi\fj!'~ iHtl;~
IWhH
11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttH,.,.,.,"H-tHtftHlt!"
1000
,I/"" ill
f!: ;41:
800
I
j'.
;I
I; I
600
,I
400
'li'V:~ !~
!,.,;
.1'
,17:
it-.
~,
4tl
LHI II
H+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r,
..•
2.5
t,
o
5
c
; ,.
'111l!' II
,.
:lji , 'I
"I'
'-'
1.
fi:
. fIT
,
,
II
!:i:
II;:I!!
lilii
,.
.
n
(MIClONS)
'I:
til
ill
'illl
'i
,
" "
1'-'
" "
:1
-l-'-t­
"
20
Fig. 9-7 - Spectrum of solution containing 15% isopropyl alcohol, 55%
toluene, and 30% methyl ethyl ketone in a 0.025 mm cell
FREQUENCY (CM')
4000
3600
'+' '.'
3200
11 _.' ; _~;
I r-
2800
2400
2000
1800
1600
'I;
J, ~ftJ.
I
.1
.,
II
I ,
..•
"""""'I
1200
j~, l.A..i i Ie. j,:., i i
I II. \:
!
I
I
:1
it
"
ii
1400
0
I
1000
800
II' ',I,
I
600
! .I.'"
,J
I,I
400
: j 'I
'I 'I
Iii
I
It:
10
11
12
13 1"
16
'8
20
2S
Fig. 9-8 - Spectrum of solution containing 200/0 isopropyl alcohol, 45%
toluene, and 35% methyl ethyl ketone in a 0.025 mm cell
9/74
Page 9-7
FREQUENCY (CM'l
~ooo
3600
3200
2800
2~00
2000
1800
1600
1~
1200
1000
800
600
400
Fig. 9-9 - Spectrum of solution containing 250/0 isopropyl alcohol, 440/0
toluene, and 31 % methyl ethyl ketone in a 0.025 mm cell
FREQUENCY (CM')
2..00
2000
1800
1600
1..00
1200
1000
800
600
Fig. 9-10 - Spectrum of solution containing 350/0 isopropyl alcohol, 200/0
toluene, and 450/0 methyl ethyl ketone in a 0.025 mm cell
"
FREQUENCY (CM')
.. 000
3600
3200
2800
1400
2000
1800
1600
1~
1200
1000
800
600
Fig. 9-11 - Spectrum of solution containing 50% isopropyl alcohol, 140/0
toluene, and 360/0 methyl ethyl ketone in a 0.025 mm cell
9/74
w
0.800
I.SOO
0.700
1.400
0.600
1.200
0.500
w
z<(
1.000
u
u
z
<{
~ 0.800
~ 0.400
ofJ)
51
m
~ 0.300
<{
0.600
0.200
0.400
0.100
0.200
0'----:-:10::---2'0
;0
40
~5L'O----l60
o
% BY VOLUME ISOPROPYL ALCOHOL
10
20
30
40
% BY VOLUME TOLUENE
Fig. 9-13 - Plot of volume percent
toluene vs. absorbance obtained from
695 cm- 1 absorption band in Figs. 9-7
through 9-11
Fig. 9-12 - Plot of volume per~ent
isopropyl alcohol vs. absorbance
obtained from 817 cm -1 absorption
band in Figs. 9-7 through 9-11
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions (% by volume):
Solution
A
B
C
D
Isopropyl Alcohol
Toluene
50
27
20
10
15
23
40
70
Methyl Ethyl Ketone
35
50
40
20
Obtain at least two spectra for each solution, determine A or %T for toluene
(at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution, and pre­
pare plots of absorbance vs. concentration on linear graph paper (or 0/0
transmittance vs. concentration on semilog paper), as shown in Figure
9-12 (or
9-14), for each solvent. Now, obtain at least two spectra
of a solution containing the three solvents in an unknown proportion. (As
a check on results, have a coworker make up the unknown solution with
accurately measured quantities of each solvent, and have him or her record the
9/74
Page 9-9
composition for comparison with
the experimental results.) De­
termine A or %T for toluene and
isopropyl alcohol from the spectra
of the unknown. and using the cal­
ibration curve plotted from the
standard soLutions, determine
the composition of the unknown
solution.
90
80
70
60
I.&J
U
Z
~
50
!::
::;
If)
Z
«
a:
40
l­
Important: Do not use the curves
given in Figures 9-12 through 9-14
to determine the composition of
your unknown. Calibration data
must be obtained from the
spectrophotometer that is used
to measure the absorbance of
the unknown if reliably accurate
results are to be obtained.
Even different instruments of
the same model may not yield
sufficient accuracy. although
results will generally be better
than those obtained from different
models.
i;?
30
200
10
20
30
40
50
60
% BY VOLUME ISOPROPYL ALCOHOL
Fig. 9-14 - Semilog plot of percent T
volume percent isoprryl alcohol
as obtained from 817 cm- absorption
band in Figs. 9-7 through 9-11
VB.
9/74 Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM')
4000
3600
_
H
90
3200
2000
1800
I
r-­
f-J--
~ _1.1 ~O~
~t t~p.1J I
C-H..
.I
i!~T
-..
~;:t
IT""""'
. .~ ~
Y'H,
···l~;t~I::t'--·f--
:J. .
~ 50
~
.~
.
Associated N-H OH
+
i ,,'
:E 40 ..
'I
+-
'
~ 30
,L
I
rr
20 H
1
I
1
. f4- ~
~ 1 N-H I.
h!r~~ s .h:r Nfst
10
o
I+r.'i
I-
,
.
'
t
if' -
'
E
e=.
C
l
.
t-- f~+-
_.
U")
Z
....... .... Hio-
h~L_,
I..>
1"'"'-'f1ll- tffU-·I···
,!-ot-,....
I
+ N-H
- til If'
, I:'
' I'
1200
1000
800
650
Ii
1
s'
'
1
1
.~
elf!
C"'''''
It H~
V ~
f--·~¥r·--·~
.,+­
Sin Ie-Bond Stretch
~L<f··
'--
J
8=0
Do,
I"
n"
C'
.-:_m..
~~ .~-~ ~'
ble~
C=8
r--'----l--'
...:.
.
•
1
1
~ ~
C=N N=O I
N pouhh.e-B nd
,,;;l:trh
~
......
L_il CL_r-­
ond Stre ch
---
0
I C-Cl
~
~
"d
l'1
St etcl
... ~
•
I
[
S4
S.
I nnn._ . . . __ .I}:;
f:;onj \lgatE d an Ar mat c Dc uble
8trtotch
leone St,I,d.ch
~_.
•.
-r--•
....
2::.S.IU
1- -
I
•
f----
Hydrogen Bending
H
~~~f+~ht-.-r-.'r--.~~4'
LJVU,
',I~t ::t~~ B~ ____ r---t-'
[
.:I
=.
VH'~
r---._ .----
'1
C=O
~ 60 UI~' sclP4·1- S~'ellllt ~t ect~~ e c~ _~= ~
"
1400
J
Hydrogen Stretchin~
80
U
1600
1
100
70
2400
2800
1
­
L
C-F
J
jC~Sin~le4nd.$.r.e.t4L-i-+-~
I)Q
(l)
>­....,
....
9/74
NRC BULLETIN No. 6
INFRARED SPECTRA OF ORGANIC COMPOUNDS:
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
R.N: JONES
NATIONAL
RESEARCH
COUNCIL
OTTAWA
1959
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL, OTTAWA, CANADA CONTENTS
I. Introduction
II.
Characteristic Group Frequencies of Hydrocarbons
1. 3600 - 1700 cm. -1
II. 1700 - 700 cm.-l
Chart I Chart II
III. Characteristic Group Frequencies of Oxygenated Compounds 1.
II.
3700 - 2000 cm. -1 2000 - 800 cm. -1 Chart III Chart IV IV. Characteristic Group Frequencies of Nitrogen, Phosphorus and Sulfu'r Compounds 1. 3600 - 1700 cm.-1
II. 1700 - 900 cm. -1 Chart V
Chart VI V. Overtone Bands of Substituted Benzenes Table I VI. C = C Stretching Bands of Linear Olefins
Table II VII. C - H Out-of-plane Bending Bands of Linear Olefins
Table III VIII. C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV IX. Carbonyl C = 0 Stretching Bands
X. Bibliography
Table V INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade, the literature on the infrared spectra
of organic compounds has expanded at an ever increasing rate, and
much of this work has been concerned with establishing character­
istic group frequencies. These data have been summarized and
critically reviewed in recent monographs by Bellamy (1). BrUgel (2),
Jones and Sandorfy (3) and Lecomte (4). They have also been tabu­
lated in a more condensed form in the widely used "Colthup Chart"
(5), which has passed through several revisions since its first pub­
lication.
In these articles the authors have endeavored to bring together
complete collections of the structure-spectra correlations, and the
newcomer to the field is liable to be overwhelmed when first con­
fronted by such a formidable mass of semi-empirical data.
The Charts publish~d in this Bulletin make no pretense at such
a complete coverage of the subject. They were initially prepared in
connection with an introductory course of lectures on chemical spec­
troscopy given recently at Ottawa University. The correlations to be
included were selected as the Inost commonly used in this laboratory,
and their choice probably reflects to some extent our preoccupation
with the structural identification of naturally occurring organic com­
pounds and their degradation products.
In the three series of charts, the characteristic group frequen­
cies associated with hydrocarbons, oxygenated compounds, and com­
pounds containing other elements, are dealt with separately. The
student is advised first to memorize the individual charts separately
and then to integrate them to obtain the overall picture.
In Tables I - V more detailed sub-divisions of the more impor­
tant group assignments are given. It must be stressed that the
ranges given in these Tables are only representative values; they
are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide. The possibility of varia­
tions outside of these ranges must be kept in mind, and the chemist
should read the appropriate sections of the texts cited above ""here
these group assignments are critically evaluated.
Finally, as he becomes increasingly familiar with these cor­
relations. the student can amplify and extend them by consulting the
more detailed texts.
R. N. Jones
Division of Pure Chemistry
National Research Council
April lOth, 1959.
CHART
CHARACTERISTIC
3500 em-I
I
t
3300
CIIC-H
!e -H
st;~t~hl
=
GROUP
I
FREQUENCIES
3000
2500
I
I
£1 1211!11 II d
i
OF
HYDROCARBONS - I 2000
~
I
=
III
r
2260- 2190 +
R-Ci5C-R
3100-3000
IC II C s tretchl
C=C-H
</>-H
-c-c­
'c/
2140-2100
R-Ci5C-H
rc=~t~hJ
H2
CHlIX
CH 2 X2
'c-c-c/
[C~~~tchl
!C=C stretch!
1980
3000- 2800
-CH2 ­
-CHa
@=HS~
/
- -
"
2000- 1650
AROMATIC
OVERTONES
C - H out of plone
bend
SEE TABLE
r
CHART II
CHARACTERISTIC
1700 em-I
GROUP FREQUENCIES OF HYDROCARBONS -
1300
1500
1100
1680-1650
1070
CHI
>C -c-o<
NON ­ CONJUGATEO
1467
ALIPHATIC
NON-CYCLIC
CHe
I
C=C stretcn
I
SEE TABLE ]I
1455
ALICYCLIC
. Iscillor I
CaC stretch
IZZZZ1
~
870-670
AROMATIC
RING
IOUi'017
out of plone
/0"
CH,
C-H bend
-C--o­
SEE TABLE III
AROMATIC
RING
980-690
,
1420-1406
C-C CYCLIC
I
IC--::;-b ~ ~ I
1500 APPROX.
1680-1580
C-C-C-C
700
Ilym. slretch I
SYM.
C-C
900
J
1
1380-1375
n
O-C-H /C- CHI
I
out of plone C-H in plone
bend
1600 (APPROX,l
DOUBLET
AROMATIC RING
I
C-H bend 1390-1360
1460
skeletol
ASYM.
CH.
I C=H I>~~dl
GEM-DIMETHYL
ISOPROPYL
TERT. BUTYL
Iym. CH,
bend
SEE TABLE
m
720-718
-(OH 1­
1i:4
I
C-H rock
I
~i.I m
CHART
CHARACTERISTIC
GROUP
FREQUENCIES
3500
OF
OXYGENATED
3000
I
2500
I
I
I
I
I
I
t ;5~St:1: t tit
I:'.:~ZZ?~fT·"""'''W'f' 1',-LLo 17777777771
7777? 77777???????
3. . .
free O-H
stretch
I 3500-3300
bonded O-H
stretch in
3635-PR.
polymers
3623- SEC.
3615-PHENOL.
III
3050-2990
bonded 0- H
C-H stretch
carboxyli c acid
H
dimers,enolized
H
/ '0/' (weak)
,B-diketones,
tropolones etc.
I
3600-3500
o -H
Tr
1
2720
stretch
2832-2815
band
C-H stretch in
C-H stretch
complex
in methoxy
3500':'3480
O-H stretch
alcohol
dimer
compounds
2000
I
I
I
1
2650 2400
0-0 stretch in
deuterate d
alcohols
stretch in
in epoxides
....... C--C.......
3615 - TERT.
COMPOUNDS -I
olciehydes
CHART III
CHARACTERISTIC
1950
1600
I
I
GROUP FREQUENCIES OF OXYGENATED
COMPOUNDS -
n
carbonyl C= 0 streich
TABLE :l1:
1600
1400
I
a:x:r-=
1610-1550
carboxylate ion
/0
osym.
C~'O - slrelc!>
1200
1000
800
I
I
I
I
~~'I I~',I, II':"::: """ i' 2i , l i If
1430-1400
I
I
•
a
melhylene
C-H scissor
in lIetones and
esters
I
1420 -1390
o-H
bend in
alcohols
(very weak)
1000
1270-1150
1i:~.9 H
o
*
-C-O-R
streIch In
est.rs
leoo
1270 ¢-COOR
1257 -12 32 CH, COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190
R - COOR
1185 -1175
H - COOR
1175-1155
R-COOCH,
I
1275-1010
R -0- R Qsym. streIch in ether'
t275 - 1200 CONJUGATED
1260 -1200
AROMATIC
1150 - 1070
ALIPHATIC
stretch in
alcohols
PHE~OLS
1150-1140
TERT.
1120-1100
SEC.
1075 1010
PRIMARY
1100-1000 CYCL.OHEXANOL
TYPE
CHART J[ CHARACTERISTIC
GROUP FREQUENCIES OF NITROGEN, PHOSPHORUS, SULFUR COMPOUNDS ­
3500 cm-'
I
3000 2500
I
I
I
t
3500-3060 bonded
=
+
2600- 2550
free N·H
stretch
-NH Z (2 BANDS
ASYM. AND SYM.l
)NH (I BAND)
I
=
r:tJrz:z:zJl]~
•
1
I
.,.0 2270
+
stretch
2900-2300
(AMINES
AND AMIOES)
bonded N- H
stretch in
quaternary
amine salts
2250-2225
R-C='N
(SEVERAL BANDS
COMPLEX SPECTRUM)
­
R-N=N=N
stretch
stretch
3530 ­ 3400
2000
R-N=C=O
N- H
I
2180- 2120
(AMINES AND AMIOES)
+
R-N::C
CHART
CHARACTERISTIC
NITROGEN.
1700 cm- I
I
!600
I
1500
I
k2??2272ZZ, 2 u224
t :;;;;;;;;:;;',;;:"""'"
1680- 1630
U
f'
i
[
m
....
- N ....
0
O
~ ~,::;"~" I
osym. stretch
:.:
I
1650-1600
1630-1550
-a-NOz
-N-NO z
1570-1500
-C-N0 2
1650-1590
un
'"
1650- 1500
stretchl
N_ 0
i
1370 _ 1250
1200
I
=l
;o~,,:: ';:::",1
,:
1300 -1250
0 - N0 2
1300-1250
N-NOt
1100
I
1000
1335-1310
1650-1475
I
C=O stretch
AMIDE I
1580-1475
R-CO-NHR
.... ",,0
.... S 'It
a sym. stretch
R .... S f'O
R ....
*0
900
I
=t
=
~----,
1060-1040 1- S = 0
stretch
I
R
.... S=O
'24o-H' 0
I P -0
R....
stretch 1
_ P-O-Ar
•
1050- 990
IP - 0
stretch
-P-O-R
R-CO-NH2
R -CO-NHe
I
1I
I!:Z:ZZ:2l
2 BANOS)
1650-1580
1710 - 1630 R -CO - NHR
1300
I
-
(CIS. AND TRANS
1715-1630
1715 -1675
COMPOUNDS
OF
1600-1500 C-N=O
1500- 1430 N-N=O
IAMIDE II
1
SULFUR
1680-1430
m
FREQUENCIES
1400
I
,Z???????I?II,IZ=
I C- N
GROUP
PHOSPHORUS,
P????????!?!???I??? 2? 22 n U l ? ??Z?2 UU?
::n:
1160-1130
sym. stretch
R,S"'O
R ....
~O
I
TABLE I OVERTONE BANDS OF SUBSTITUTED BENZENES PENTA
MONO
HEXA
I 2,3
TRI
1,3,5-TRI
1,2,4-TRI
n
t
z
o
I­
0.
0::
1\ ) \ \J
I 2
I 3
01
01
1.4-01
,2,3:.4 -TETRA
o
VI
CD
I
1',2,4,5-T;TRA
I
) lJ\J "
11,2,3,5-T.ETRA
~
<[
If n
\i
~
~~~~~I
1900
1100
1L
.1
I
1900
./
I ~I~~~~
1700
1900
jIJ\ ~
JV\
1700
)\
~~~~~I I~~~~~ ~~~~~
1900
WAVE NUMBER (em-I)
1700
1900
1700
1900
1700
TABLE II C=C STRETCHING BANDS OF LINEAR
Rl
H
"C=C/
"
H/
/
1662-1652
H
H
RI
H
R2/
"
R."
/RS
"
R4
"
C=C /
1675-1665
Re/
Ra
C=C
"
/C =C"
H
"C=C/
/
1678-1668 em-I
Re
Re
R,
Re
RI
OLEFINS R,
1675-1665
"
H
"c =C/
H/
1658-1648
H
"
H
1648-1638
TABLE
m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R.
"
/
/C =C,
H
995-985 em-I
910-905
R,
,
/
R;s
/C=C,
H
H
R2
H
RI
H
R"
/R2
/'c =C/
~
H
R2
R,
H
"C=C /
R2/
"
H
980-965
/c=c~
H
895-885
840-790
~690
H
TABLE IV
C
H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene
Monosubstituted benzene
1,2-Disubstituted
1,3 -Disubstituted
1,4-Disubstituted
1,2,3-Trisubstituted
1,2,4-Trisubstituted
1,3,5 -Trisubstituted
1,2,3,4-Tetrasubstituted
1,2,3,5-Tetrasubstituted
1,2,4,5-Tetrasubstituted
Pentasubstituted
Five adjacent free hydrogen atoms
Four adjacent free hydrogen atoms
Three adjacent free hydrogen atoms
Two adjacent free hydrogen atoms
One free hydrogen atom
671 cm.- 1
770-730
770 -735
810-750
833-810
780 -760
825-805
865-810
810 -800
850 -S40
870 -855
710 -690
710 -690
745-705
885-870
730-675
870
770 -730
770 -735
810-750
86O-S00
900-860
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm. -1)
KETONES
R - CO - R
R - C = C - CO - R
R - CO - Ar.
1725 -1705
1685 - 1660
1700 - 1680
1670-1660
1730-1710
1640 ­ 1540
Ar. - CO - Ar.
R - CO - CO - R
R - CO - CHZ - CO - R (enolized)
Sat. cyclic (six membered or larger ring)
Sat. cyclic (five membered ring)
Sat. cyclic (four membered ring)
Quinones (Z carbonyl groups in same ring)
Quinones (2 carbonyl groups in different ri ngs)
1:' .copolone s
1600
1725
1750
1775
1690
1655
- 1705
- 1740
- 1660
- 1635
ALDEHYDES
Usually about 15 cm. -1 above corresponding ketones.
ACIDS
R - COOH (dimer)
R - C = C - COOH (dimer)
Ar. - COOH
1725 -1700
1715 -1690
1700 - 1680
ESTERS
R - COOR
R - C = C - COOR
Ar.
R R Sat.
Sat.
- COOR
COOAr.
CO. OC = C - R
'Y'-Lactone
O-Lactone
1750-1735
1730 -1715
1730-1715
1800 - 1770
1800 ­ 1770
1780 ­ 1760
1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO. Cl
R - CO - 0 - CO
Cyclic anhydride
R - CO - 0 - 0 Ar. - CO - 0 - 0
R - CO - NH Z
R - CO - NHR
- R
(5-membered ring)
CO - R
- CO - Ar.
1815-1770
1850 - 1800
1870 - 18Z0
1820 -1810
1805-1780
1690 ­ 1650
1680 -1630
and
and
and
and
1790 - 1740
1800 - 1750
1800 -1780
1785 -1755
BIBLIOGRAPHY
(1) L. J. Bellamy. liThe Infra-red Spectra of Complex Molecules".
Second Edition. Methuen & Co. (London), John Wiley & Sons
(New York). 1958.
(2)
W. BrUgel, "Einfuhrung in die Ultrarotspectroskopie ll • Steinkopff
(Darmstadt). 1954.
(3) R. N. Jones and C. Sandorfy. "The Application of Infrared and
Raman Spectrometry to theElucidation of MOlecular Struc­
ture". Technique of Organic Chemistry. A. Weissberger.
ed. Vol. IX.
Interscience Publishers Inc.
(New York.
London). 1956.
(4) J. Lecomte, "Spectroscopie dans l'Infrarouge". Handbuch der
Physik. S. FIUgge, ed. Vol. XXVI. Springer-Verlag (Berlin.
Gtlttingen. Heidelberg). 1958.
(5)
N. B. Colthup. J. Opt. Soc. Am., 40, 397. 1950.