|
Interpreting the infrared
spectrum of propan-1-ol
CH3CH2CH2OH
[Author
©
Dr Phil Brown PhD:
Doc Brown's advanced level organic chemistry exam revision notes
suitable for students of UK A level chemistry courses & US K12 grade
11, grade 12 and AP honors chemistry courses:
Molecular
spectroscopy analysis of
propan-1-ol
[spectra page
updated Mar 26th 2026 *]
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CH3CH2CH2OH
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Infrared spectroscopy - spectra index
See also
comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 isomers of C3H8O
Introductory note on the infrared spectrum of propan-1-ol
(1-propanol)
Students and teachers please note
my explanation of the infrared
spectrum of propan-1-ol is designed
for advanced, but pre-university, chemistry courses.
Based in
the infrared spectrum diagram for propan-1-ol, only some of the most
prominent peaks for particular bond vibrations are discussed,
particularly if propan-1-ol has a functional group with a particular
characteristic wavenumber peak.
The infrared spectrum of
propan-1-ol is
unique and the whole, or selected wavenumbers, can be used to
fingerprint its identity, sometimes analysing a mixture
containing propan-1-ol or following its change of concentration in a
reaction.
Spectra obtained from a liquid film of propan-1-ol. The right-hand part of the of the
infrared spectrum of propan-1-ol, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of propan-1-ol and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of
propan-1-ol.
Propan-1-ol C3H8O,
,
,
,
primary alcohol
The molecular structure and naming of aliphatic
alcohols and ethers
Interpretation of
the infrared spectrum of propan-1-ol
The most prominent infrared absorption lines of
propan-1-ol
For propan-1-ol, the most characteristic absorption is the
broad O-H
stretching vibration band at wavenumbers ~3500 to 3200 cm-1,
the breadth is caused by hydrogen bonding interactions, common to
all hydrogen bonded molecules with a hydroxyl group e.g. alcohols
and carboxylic acids.
R-O–Hδ+llllδ–:O-R
... etc.
C-H stretching vibration absorption occurs ~2900 cm-1,
wavenumbers common to any molecule with alkyl groups such as the
propyl group in propan-1-ol.
There are wavenumber C-O and C-H vibration
absorption bands ~1350 to 1070 cm-1 for propan-1-ol.
The absence of other specific functional group bands
will show that particular functional group is absent from the
propan-1-ol
molecular
structure.
Key points about
the infrared spectrum of ethanoic acid and practice questions
Propan-1-ol’s IR spectrum shows a broad O–H stretch (3200–3600
cm⁻¹), C–H stretches (~2850–2960 cm⁻¹), and
C–O stretch (~1050–1150 cm⁻¹).
These peaks confirm the presence of a primary alcohol.
Key IR Spectrum
Features of Propan-1-ol
| Bond/Functional
Group |
Wavenumber (cm⁻¹) |
Appearance |
Notes |
| O–H stretch |
3200–3600 |
Broad, strong |
Hydrogen bonding broadens the band |
| C–H stretch (alkyl) |
2850–2960 |
Sharp |
Typical alkane C–H |
| C–O stretch |
1050–1150 |
Strong |
Diagnostic of alcohols |
| O–H bend |
~1400 |
Medium |
Supports OH presence |
| Fingerprint region |
<1500 |
Complex |
Unique to propan-1-ol |
Sources:
NIST Chemistry WebBook,
IJMRSET IR spectrum study
Common
Misconceptions
- Confusing alcohol O–H with acid O–H: Acid O–H is
broader and lower (2500–3300 cm⁻¹).
- Assuming all alcohols have identical IR spectra:
Primary, secondary, tertiary alcohols differ slightly in O–H stretch shape.
- Ignoring C–O stretch: Students often overlook this, but
it confirms alcohol functionality.
- Fingerprint region neglected: Examiners may ask why
it’s important for confirming identity.
Exam Revision Tips
- Quote approximate ranges (O–H ~3300 cm⁻¹, C–O ~1100
cm⁻¹).
- Distinguish alcohol vs. acid vs. ester spectra.
- Use multiple peaks together (O–H + C–O + C–H) to
confirm alcohol.
- Practice comparing isomers (propan-1-ol vs. propan-2-ol
versus propanal).
- Remember broad vs. sharp O–H differences.
Practice Multiple
Choice Questions based on the infrared spectrum of propan-1-ol
Each question has A–D options, model
answer, and feedback explaining distractors.
If you think there are any errors
email doc b
asap
Jot down your question responses and
check out the
ANSWERS!
Q1. Which peak
confirms the presence of an alcohol in propan-1-ol?
- Broad band 3200–3600 cm⁻¹
- Sharp peak at 1700 cm⁻¹
- Strong band at 1050–1150 cm⁻¹
- Sharp peak at 2900 cm⁻¹
Q2. Which peak
distinguishes alcohols from carboxylic acids?
- 3200–3600 cm⁻¹ broad O–H
- 2500–3300 cm⁻¹ broad O–H
- 1700 cm⁻¹ C=O
- 1050 cm⁻¹ C–O
Q3. Which molecule
lacks the O–H IR stretching vibration?
- Propan-1-ol
- Propan-2-ol
- Propanoic acid
- Propanone
Q4. Fingerprint
region (<1500 cm⁻¹) is useful because:
- It shows C=O stretch
- It uniquely identifies molecules
- It shows O–H stretch
- It shows C–H stretch
Q5. Which molecule
shows both O–H and C=O peaks?
- Propan-1-ol
-
Propanal
- Propanone
-
Propanoic acid
Q7. Why is the O–H
stretch broad in alcohols?
- Hydrogen bonding
- Instrument error
- Solvent impurity
- Coupling with C–H
Q8. Which peak would
be absent in propanone compared to propan-1-ol?
- 3200–3600 cm⁻¹ O–H
- 1700 cm⁻¹ C=O
- 2900 cm⁻¹ C–H
- 1050 cm⁻¹ C–O
Q9. Which feature
distinguishes aldehydes from alcohols?
-
C–H stretch
- O–H broad band
-
C=O at 1700 cm⁻¹
- Fingerprint region
Q10. Which
combination confirms alcohol presence?
- O–H stretch + C–O stretch
- C=O + O–H stretch
- C–H + C=O
- Fingerprint region only
If you think there are any errors
email doc b
asap
Jot down your question responses and
check out the ANSWERS!
|
Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 isomers of C3H8O
NOTE: The images are linked to their
original detailed spectral analysis pages AND can be doubled in
size with touch screens to
increase the definition to the original propan-1-ol,
propan-2-ol and methoxyethane image sizes. |
|
|
 |
 |
I wasn't able to obtain an infrared
spectrum for methoxyethane, so I've added the infrared spectrum
of ethoxyethane to enable a few comparisons with two aliphatic
alcohols
Comparing the
infrared
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane
exemplify infrared spectra of the lower members of the homologous series
of aliphatic alcohols and ethers |
|
INFRARED SPECTRA
(above): There are, as expected, differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, but most absorptions
for all three molecules are the various C-O and the many C-H
vibrational modes. However, there is one characteristic distinguishing
absorption only present in the infrared spectra of alcohols, but
not in ethers, that is the broad O-H stretching vibration
peaking at ~3350 cm-1. There is also another broad
absorption band (origin?) peaking at ~650 cm-1 in the
alcohol spectra, but not in the ether spectra. |
 |
 |
 |
Comparing the
mass
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane
exemplify the mass spectra of the lower members of the homologous series
of aliphatic alcohols and ethers |
|
MASS SPECTRA (above):
The base ion peaks are m/z 45 for propan-2-ol and methoxyethane,
but that of propan-1-ol is m/z 31. Many of the fragmentation
ions are common to all three spectra. The m/z 45 ion is peak is
much smaller in the propan-1-ol spectrum compared to the other
two. |
 |
 |
 |
Comparing the
1H proton NMR
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane exemplify the 1H proton NMR spectra of
the lower members of the homologous series of aliphatic alcohols and
ethers |
|
1H NMR SPECTRA (above): The 1H NMR spectra of
all three molecules give different integrated proton ratios for the
different 1H chemical environments i.e. the proton
ratios are as follows: propan-1-ol
3:2:2:1; propan-2-ol 6:1:1 and methoxyethane
3:2:3. Therefore, all three can be distinguished by their
1H NMR spectra. |
 |
 |
 |
Comparing the
carbon-13 NMR
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane exemplify the carbon-13 NMR spectra of
members of the lower members of the homologous series of aliphatic
alcohols and ethers |
|
13C NMR SPECTRA
(above): The
13C NMR spectra of propan-1-ol and methoxyethane show
three different 13C NMR chemical shifts, but
propan-2-ol can be distinguished from the other two by
exhibiting only two chemical shift lines. You would need other
spectral data to distinguish propan-1-ol and methoxyethane. |
Key words & phrases: CH3CH2CH2OH 1-propanol n-propyl alcohol image and diagram explaining the infrared spectrum
of propan-1-ol, complete infrared absorption spectrum of propan-1-ol, comparative spectra of
propan-1-ol, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
propan-1-ol,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of propan-1-ol, revision of infrared spectroscopy of propan-1-ol, fingerprint region analysis of
propan-1-ol, how to identify propan-1-ol from its infrared spectrum, identifying organic
compounds like propan-1-ol from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of propan-1-ol detection of
functional groups in the propan-1-ol molecule example of the infrared spectrum of a
molecule like propan-1-ol with an alcohol functional group
1-propanol n-propyl alcohol
isomer of molecular formula C3H8O
Diagram of absorption of wavenumber
peaks in the infrared spectrum of propan-1-ol 1-propanol. Characteristic peak wavenumbers in the infrared
spectrum of propan-1-ol 1-propanol. Finger print identification pattern using the infrared
spectrum of propan-1-ol 1-propanol. Revision notes on the infrared spectrum of
propan-1-ol 1-propanol. Matching
and deducing the structure of the propan-1-ol 1-propanol molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic primary alcohols, infrared spectra of
propan-1-ol 1-propanol, an isomer of molecular formula C3H8O Explanatory diagram of the infrared spectrum of the 2-propanol propan-2-ol molecule in terms of its molecular structure. Listing data of the prominent main wavenumber peaks troughs in the infrared spectrum of 2-propanol propan-2-ol. How to explain the infrared spectrum of 2-propanol propan-2-ol. Use of the infrared spectrum of 2-propanol propan-2-ol, identification of 2-propanol propan-2-ol from its infrared spectrum - fingerprint wavenumber pattern to identify the 2-propanol propan-2-ol molecule. The uses of the infrared spectrum of the 2-propanol propan-2-ol molecule. The distinctive features of the infrared spectrum of the 2-propanol propan-2-ol molecule explained. explaining the peaks-trough of the transmittance of the infrared spectrum of 2-propanol propan-2-ol what does the infrared spectrum tell you about the structure and properties of the 2-propanol propan-2-ol molecule? How do you interpret the infrared absorption spectrum of
propan-1-ol How
to interpret the infrared spectrum of propan-1-ol Explanatory diagram of the
infrared spectrum of the propan-1-ol molecule in terms of its molecular
structure. Listing data of the prominent main wavenumber peaks
troughs in the infrared spectrum of propan-1-ol. How to explain the infrared
spectrum of propan-1-ol. Use of the infrared spectrum of propan-1-ol, identification
of propan-1-ol from its infrared spectrum - fingerprint wavenumber pattern
to identify the propan-1-ol molecule. The uses of the infrared spectrum of
the propan-1-ol molecule. The distinctive features of the infrared spectrum
of the propan-1-ol molecule explained interpretation diagram explaining the
peaks-trough of the transmittance of the infrared spectrum of
propan-1-ol
what does the infrared spectrum tell you about the structure and
properties of the propan-1-ol molecule? How is infrared spectrum of
propan-1-ol used
to identify propan-1-ol?
ANSWERS to the
Practice Multiple Choice Questions based on the infrared spectrum of
propan-1-ol
If you think there are any errors
email doc b
asap
Q1. Which peak
confirms the presence of an alcohol in propan-1-ol?
- Broad band 3200–3600 cm⁻¹
- Sharp peak at 1700 cm⁻¹
- Strong band at 1050–1150 cm⁻¹
- Sharp peak at 2900 cm⁻¹
Answer: A.
- Correct: O–H stretch.
- B = carbonyl (not alcohol).
- C = C–O stretch (supportive but not unique).
- D = alkyl C–H.
Q2. Which peak
distinguishes alcohols from carboxylic acids?
- 3200–3600 cm⁻¹ broad O–H
- 2500–3300 cm⁻¹ broad O–H
- 1700 cm⁻¹ C=O
- 1050 cm⁻¹ C–O
Answer: C.
- Alcohols have no C=O group
Q3. Which molecule
lacks the O–H IR stretching vibration?
- Propan-1-ol
- Propan-2-ol
- Propanoic acid
- Propanone
Answer: D.
- Ketones have C=O, no O–H.
Q4. Fingerprint
region (<1500 cm⁻¹) is useful because:
- It shows C=O stretch
- It uniquely identifies molecules
- It shows O–H stretch
- It shows C–H stretch
Answer: B.
Q5. Which molecule
shows both O–H and C=O peaks?
- Propan-1-ol
- Propanal
- Propanone
- Propanoic acid
Answer: D.
- Acid has both O–H and C=O.
Q7. Why is the O–H
stretch broad in alcohols?
- Hydrogen bonding
- Instrument error
- Solvent impurity
- Coupling with C–H
Answer: A.
- Correct: hydrogen bonding broadens.
Q8. Which peak would
be absent in propanone compared to propan-1-ol?
- 3200–3600 cm⁻¹ O–H
- 1700 cm⁻¹ C=O
- 2900 cm⁻¹ C–H
- 1050 cm⁻¹ C–O
Answer: A.
Q9. Which feature
distinguishes aldehydes from alcohols?
- C–H stretch
- O–H broad band
- C=O at 1700 cm⁻¹
- Fingerprint region
Answer: C.
- Aldehydes show C=O, alcohols show O–H.
Q10. Which
combination confirms alcohol presence?
- O–H stretch + C–O stretch
- C=O + O–H stretch
- C–H + C=O
- Fingerprint region only
Answer: A.
- Correct: O–H + C–O together confirm alcohol.
If you think there are any errors
email doc b
asap
Links associated
with propan-1-ol
(1-propanol)
The chemistry of ALCOHOLS
revision notes INDEX
The mass spectrum of Propan-1-ol (1-propanol,
n-propyl alcohol)
The H-1 NMR spectrum of Propan-1-ol (1-propanol,
n-propyl alcohol)
The C-13 NMR spectrum
of Propan-1-ol (1-propanol,
n-propyl alcohol)
Infrared spectroscopy index
Isomers of molecular formula C3H8O
(Mr = 60)
ALL SPECTROSCOPY INDEXES
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the spectroscopy of propan-1-ol (1-propanol) - its 13C NMR spectrum are
suitable for use of pre-university students studying AQA advanced level
chemistry, Edexcel advanced level chemistry, OCR advanced level chemistry, IB
advanced level chemistry, WJEC (Eduqas) advanced level chemistry, CIE Cambridge advanced level chemistry, US grade 11-12 AP honors
chemistry courses and they will also prove useful to
1st year undergraduate students of chemistry. |
