Adrianna Fernandez
903573483
CHEM 2380 B03, 90269
Introduction
Three unknown compounds will be identified using Infrared Spectroscopy (IR) and
Nuclear Magnetic Resonance Spectroscopy (NMR). The three unknowns could be any of the
following compounds: 4-ethoxyphenol, 4-ethylphenol, 4-hydroxybenzoic acid, 4isopropylphenol, 4-methoxyphenol, acetophenone, ethanol, ethyl acetate, isopropanol, and
isopropyl acetate.
Theory
IR spectroscopy will be used to identify possible functional groups in the unknown
compounds. Infrared light is passed through the sample and the light absorbed by a molecule
corresponds to the energy required to cause vibrations of specific bonds. This information is
depicted on an IR spectrum graph of transmittance (how much light was not absorbed by the
sample) vs. frequency.
NMR Spectroscopy gives information about different proton environments in a molecule
and will be used to build the structure of each unknown. The radio frequency a hydrogen nucleus
absorbs is dependent upon the external environment of the nucleus. The multiplicity (singlet,
doublet, triplet, etc.) of a signal is the number of protons seen by the proton of interest plus one,
and the integration is the relative number of protons per signal. The chemical shift is the location
on the x axis of each signal and depends on the electronegativity of the neighboring groups.
Chemical shift, multiplicity, and integration are distinct for different proton environments and
can be used to identify and build an unknown structure.
Results
Unknown compound M IR spectra results
Wavelength
Functional groups
3400
-OH
3100
Csp3-H
3000
Csp2-H
Adrianna Fernandez
903573483
Unknown compound E IR
Wavelength
Functional groups
3500
-COOH
3150
Csp3-H
3000
Csp2-H
1600
C=O
Unknown Compound L IR
Wavelength Functional groups
2950
Csp3-H
1750
C=O
Unknown compound M NMR
Chemical Shift
Multiplicity Integration
1.7
Triplet
3H
4
Quartet
2H
6.9
Doublet
2H
7.1
Doublet
2H
9
Singlet
1H
Unknown compound E NMR
Chemical Shift
Multiplicity Integration
2.1
Singlet
3H
7.1
Doublet
2H
8
Doublet
2H
12.5
Singlet
1H
Unknown compound L NMR results
Chemical Shift
Multiplicity Integration
1.25
Doublet
6H
2
Singlet
3H
5
Septet
1H
Discussion
CHEM 2380 B03, 90269
Assignment
-CH3
-CH2-O
Para-substituted ring
Para-substituted ring
-OH
Assignment
Methyl attached to benzene ring
Para-substituted ring
Para-substituted ring
Carboxylic acid
Assignment
CH3 in Isopropyl group
-CH3
CH in Isopropyl group
Unknown compound M IR spectra possesses a distinct large broad spike at 3400 cm-1
which matches the literature value for an alcohol group (3000-3600 cm-1, broad peak) suggesting
that sample M is an alcohol and eliminates other possible molecules without at least one OH
group. There were 5 proton environments discovered through NMR. The first signal detected for
unknown sample M was a triplet at 1.7 ppm with an integration of 3H indicating this proton
environment is a methyl group (integration of 3H) attached to a CH2 (triplet multiplicity) since
alkyl electronic environments possess a chemical shift of 0-2 ppm. The second proton
environment is a quartet at 4 ppm with an integration of 2H matching the literature value (3-5
Adrianna Fernandez
903573483
CHEM 2380 B03, 90269
ppm) of a proton next to a N, O, or X group and the multiplicity (quartet) indicates this proton
environment is next to a methyl group (since no other possibilities have functional groups with 3
hydrogens); the integration of 2H suggests the second proton environment has two protons. The
second proton environment is a quartet with a chemical shift of 4 ppm and an integration of 2H
suggesting that this proton environment is a CH2 group (integration of 2H) between a methyl
(quartet multiplicity) and oxygen (chemical shift of 3-5 ppm and no N or X in possible
compounds). The third and fourth proton environments (2 doublets at 6.9 and 7.1 both with an
integration of 2H) matches the literature values of a para-substituted benzene ring (2 doublets
with an integration of 2H at 6.5-8.5 ppm) suggesting that unknown compound M is a parasubstituted benzene ring. This evidence should eliminate all mono-substituted benzene rings and
alkyl chains in the possibilities. The fifth proton environment is a singlet at 9 ppm with an
integration of 1H that matches the characteristics of an OH group: the chemical shift is 9-12
ppm, the multiplicity is a singlet (meaning that proton sees no other protons), and the integration
is 1H (only 1H in OH) which corroborates the IR spectra that unknown compound M is an
alcohol. The five proton environments identified using NMR for unknown compound M are
characteristic of 4-ethoxyphenol because there is a methyl next to a CH2 (first proton
environment: triplet, 1.7 ppm, 3H), a CH2 between an oxygen and methyl group (second proton
environment: quartet, 4 ppm, 2H), a para-substituted benzene ring (third and fourth proton
environments: 2 doublets, 6.9 ppm and 7.1 ppm, 2H and 2H), and an alcohol (fifth proton
environment: singlet, 9 ppm, 3H).
Unknown compound E IR spectra has a sharp peak at 1600 cm-1 which matches the
literature value for a carbonyl group (1600-1800 cm-1) suggesting that sample E has a carbonyl.
The IR spectra for sample E also has a broad peak at 3300 cm-1 which matches the literature
Adrianna Fernandez
903573483
CHEM 2380 B03, 90269
value for an alcohol group (3000-3600 cm-1, broad peak) suggesting that this unknown sample
possesses an OH group. From the IR spectra, all possibilities without a carbonyl and alcohol can
be eliminated. Compound E possesses 4 proton environments through NMR. The first proton
environment is a singlet at 2.1 ppm with an integration of 3H indicating that this proton
environment is a methyl group (3H) around allylic/benzylic groups (2-3 ppm) next to no other
protons (singlet). The second and third proton environments (2 doublets at 7.1 ppm and 8 ppm,
both with an integration of 2H) matches the literature value for a para-substituted ring (2
doublets with an integration of 2H at 6.5-8.5 ppm) suggesting that compound E is a parasubstituted ring. All mono-substituted rings and alkyl chains can be eliminated as possibilities for
compound E. The fourth proton environment is a singlet at 12.5 ppm with an integration 1H
matches the literature values of a proton in a carboxylic acid (10-12 ppm, singlet, 1H) suggesting
that compound E is a carboxylic acid and is also supported by evidence in IR spectra. Unknown
sample E has four proton environments: a singlet at 2.1 ppm with an integration of 3H indicating
a methyl (3H) in an allylic/benzylic environment (2-3 ppm), 2 doublets at 7.1 ppm and 8 ppm
both with an integration of 2H suggesting a para-substituted ring (2 doublets with a integration of
2H at 6.5-8.5 ppm), and a singlet at 12.5 ppm with a integration of 1H indicating a carboxylic
acid (10-12 ppm, singlet, 1H integration); These proton environments of sample E are all
characteristic of p-toluic acid which has five proton environments: carboxylic acid (10-12 ppm,
singlet, 1H integration), para-substituted ring (2 doublets with a integration of 2H at 6.5-8.5
ppm), methyl next to benzene ring (singlet at 2-3 ppm, 3H integration).
Unknown compound L IR spectra possesses a spike at 2950 cm-1 which matches
literature values for Csp3-H (2700-3000 cm-1) suggesting that compound L has Csp3 groups.
Sample L also has a spike at 1750 cm-1 in its IR spectra which coincides with the literature
Adrianna Fernandez
903573483
CHEM 2380 B03, 90269
values of a carbonyl group (1600-1800 cm-1) suggesting sample L possesses a carbonyl group
and possibilities without a carbonyl can be eliminated. Using NMR spectroscopy, sample L has
three proton environments. The first and third proton environments (doublet with 6H at 1.25 ppm
and Septet with 1H at 5 ppm) is characteristic of an isopropyl group (doublet with 6H and Septet
with 1H). The second proton environment is a singlet at 2 ppm with an integration of 3H and is
indicative of a methyl group (3H at 0-2 ppm). It is important to note that there was no indication
that compound L contains an aromatic ring so, all aromatic rings can be eliminated as
possibilities of the identity of L. The only compound that is not an aromatic ring that contains an
isopropyl group from the possibilities is isopropyl acetate. Unknown sample L has 3 proton
environments: a singlet at 2 ppm with an integration of 3H indicating the methyl (3H) end of an
alkyl chain, a doublet at 1.25 ppm with a integration of 6H indicating of the methyl ends of an
isopropyl group (doublet with 6H and Septet with 1H), and a septet at 5 ppm with a integration
of 1H indicating the CH in an isopropyl group (doublet with 6H and Septet with 1H); The proton
environments are characteristic of isopropyl acetate which should have three proton
environments: a doublet with a integration of 6H at 0-2 ppm (methyl ends of isopropyl group), a
septet at 3-5 ppm with a integration of 1H (the CH in an isopropyl group next to an oxygen), and
a singlet at 2-3 ppm with a integration of 3H (methyl alpha to carbonyl).
Conclusion
Using NMR spectroscopy and IR spectroscopy three unknown compounds (E, L, and M)
were identified out of twelve possibilities. Compound E is p-toluic acid, Compound L is
isopropyl acetate, and compound M is 4-ethoxyphenol.
Adrianna Fernandez
903573483
Appendix
Unknown Compound L IR spectra
Unknown Compound M IR spectra
CHEM 2380 B03, 90269
Adrianna Fernandez
903573483
Unknown Compound E IR spectra
NMR Spectra
CHEM 2380 B03, 90269