Absorption Spectroscopy
Type of Radiation
Energy (kcal/mol)
Frequency
Molecular
Interaction
Wavelength
Translation
Microwave
0.001 - 1
1 - 400 cm-1
Molecular
Rotations
Rotation of the molecular
as a whole about its center
of mass
400 - 4,000 cm-1
Molecular
Vibrations
Stretching and binding
of bonds
Infrared
1.1 - 11
Visible
50 - 75
400 - 600 nm
Ultraviolet
75 - 150
200 - 400 nm
Electronic
Excitation
Promotion of electrons to
higher energy levels
Infrared Absorption Spectroscopy
4000 cm-1
2000 cm-1
X-H
Region
2500 - 4000 cm-1
C-H N-H O-H
Stretching
SP
X=Y
Region
Region
2000 ­
2500 cm-1
1500
2000 cm-1
C=C
C=N
Stretching
400 cm-1
1500 cm-1
C=C
C=O
C=N
Stretching
Fingerprint
Region
400 - 1500 cm-1
Single Rond Stretching
Bond Bending
Polyatomic Vibrations
Figure by MIT OCW.
Infrared Spectra: Tables of Reference
X-H Region
Phenols and Alcohols
ROH
3700-3500 sharp
or 3200-3600 broad(H-bonded)
Acids
RCO2H
2800-3600 very broad
Amides and Amines
RCONHR
R2NH
3300-3500
C-H bonds
C C H
C C H
C C H
RCHO
3100-3300
3000-3200
2850-3000
2700-2800
sp Region
Acetylenes
Nitriles
Ketenes
Allenes
C
C
C
C
C
N
C O
C C
2100
2200
2150
1950
Double Bond Region
Alkenes
Imines
Nitro
C C
C N
NO2
1600-1670 weak unless conjugated
1600-1700
1350-1550(two bands)
Carbonyl Groups
Note: subtract ca. 30 cm-1 for conjugation (e.g.
with a double bond or aromatic ring)
Anhydrides
RC(O)OCOR
Acid Chlorides
RCOCI
Esters
Acids
1710
RCO2H
1700-1725
1740
O
1715
1780
1740
O
NR
O
O
O
O
1770
O
1700
1720-1740
1680
O
O
1630-1700
O
O
1790-1815
1725-1755
Urethanes
R2NCO2R
Aldehydes
RCHO
O 6-membered and larger cyclic ketones
1740-1780,
1800-1840
(two bands)
RCO2R
Amides
RCONR2
Ketones
(subtract ca. 30 cm-1 for
R2C O 1710 conjugation)
1690-1740
O
1730
NR
1650
Figure by MIT OCW.
Regions of the 13C NMR Spectrum
Aromatic
120-160 ppm
Carbonyls
150-220 ppm
200
180
C-O, N
40-90 ppm
Alkenyl
100-150 ppm
160
140
120
Alkynyl
70-90 ppm
100
80
Alkyl
0-50 ppm
60
40
20
0
Chemical Shift (�)
Figure by MIT OCW.
Characteristic Functional Group Chemical Shifts in 13C NMR (ppm)
Alkanes
Methyl (RCH3)
Methylene (RCH2R’)
Methine (RCH(R’)(R”))
Quaternary (RC(R’)(R”)(R’’’))
Alkenes
Aromatic
Alkynes
Nitriles
Alcohols, Ethers
Amines
0-30
15-55
25-55
30-40
100-150
120-160
70-90
110-125
50-90
40-60
Organohalogen
C–F
C–Cl
C–Br
C–I
Ketones, Aldehydes
Carboxyl Derivatives
Acids
Esters
Amides
Carbamates
70-80
25-50
10-40
–20-10
185-220
150-185
155-180
150-180
150-160
1
H NMR Spectra: Tables of Reference
Average Chemical Shifts (�) of �−Hydrogens
in Substituted Alkanes*
CH3X
X
RCH2X
R2CHX
0.9
1.25
4.4
3.4
3.3
1.25
1.5
F
Cl
Br
0.233
0.9
4.26
3.05
2.68
I
OH
OR
OAr
OCOR
2.16
3.47
3.3
3.7
3.6
3.2
3.6
3.4
3.9
4.1
4.2
3.6
OCORAr
SH
SR
SOR
SO2R
3.8
2.44
2.1
2.5
4.2
2.7
2.5
5.1
2.8
2.9
3.1
NR2
2.2
2.9
2.6
2.9
H
CH3 or CH2
NR-Ar
NCOR
NO2
CHO
COR
COAr
COOH
COOR
CONH2
1
CR=CRCR
Phenyl
Aryl �
�
C CR
C CN
2.8
4.28
2.20
2.1
2.6
2.07
2.1
2.02
2.0-1.6
2.3
3.0-2.5
2.0
2.0
4.0
4.1
5.0
2.8
4.4
2.3
2.4
3.0
2.3
2.3
2.2
2.3
2.7
3.2
4.7
2.4
2.5
3.4
2.6
2.6
Chemical Shifts of Hydrogens Bonded to
Unsaturated Centers
Unconjugated
Conjugated*
R2C=CH2
4.6-5.0
5.4-7.0
R2C=CHR
5.0-5.7
5.7-7.3
Aromatic
6.5-8.3
Nonbenzenoid
aromatic
6.2-9.0
Acetylenic
2.3-2.7
2.7-3.2
Aldehydic
9.8-9.8
9.5-10.1
R2NCHO
7.9-8.1
ROCHO
8.0-8.2
Type
* The position depends on the type of functional
group in conjugation with the unsaturated group.
Chemical Shifts of Hydrogen Bonded to
Oxygen, Nitrogen, and Sulfer
Functional Group
OH
2.6
2.9
NH2
2.3
2.7
Chemical Shift, �
Alcohols
0.5
0.5-5
(Monomeric)
(Associated)
Phenols
(Monomeric)
(Associated)
Enols
4.5
4.5-8
15.5
RCO2H
9-12
(Dimeric)
H-bonded to C=O
13-16
Alkylamine
0.6-1.6
Arylamine
2.7-4.0
Amide
7.8
Alkylamine,
0.3-0.5
Arylamine
2.7-2.8
* The tabulated values are average values for
compounds that do not contain another functional
group wlthin two carbon atoms from the indicated
hydrogens.
NH
R3NH+
Ammonium salts
7.1-7.7 (in CF3COOH)
Includes polycyclic and many heterocyclic
aromatics.
SH
Aliphatic
Aromatic
1.3-1.7
2.5-4
�
Figure by MIT OCW.
�
1H NMR Coupling Constants (Expanded)
H
geminal 12-15 Hz
acyclic
can be 0-25 Hz in
cyclic system
H
H
6-8 Hz
vicinal
(averaged by free rotation)
H
In rigid systems, vicinal coupling can range from 0 to 15 Hz. For example:
H
H
ax-ax
H
H
6-14 Hz
H
ax-eq
0-5 Hz
H
H
H
eq-eq 0-5 Hz
Spin-spin coupling in alkenes:
H
geminal
0-3-Hz
H
H
H
trans
12-18 Hz
cis
H
6-12 Hz
allylic 0-3 Hz
H
Spin- spin coupling in arenes:
Ha
Hb
Hc
Hd
Jab (ortho)
6-10 Hz
Jac (meta)
1-3 Hz
Jad (para)
0-1 Hz
Note: Structures shown above represent
generic coupling situations and not the
specific molecules depicted (in which
the labeled protons would be chemically
equivalent and would not couple).
Figure by MIT OCW.