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Interpreting the infrared spectrum of
1-chlorobutane
[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 - analysing the infrared spectrum of 1-chlorobutane
[updated
Mar 11th 2026 *]
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infrared spectrum of
CH3CH2CH2CH2Cl
LINKS associated
with 1-chlorobutane
The
chemistry of organic halogen compounds
This is a BIG
website, you need to take time to explore it
Infrared spectroscopy - spectra index
See also
Comparing infrared, mass, 1H NMR & 13C NMR
spectra of the 4 structural isomers of C4H9Cl
Introductory note on the infrared spectrum of 1-chlorobutane
Students and teachers please note
my explanation of the infrared
spectrum of 1-chlorobutane is designed
for advanced, but pre-university, chemistry courses.
Based in
the infrared spectrum diagram for 1-chlorobutane, only some of the most
prominent peaks for particular bond vibrations are discussed,
particularly if 1-chlorobutane has a functional group with a particular
characteristic wavenumber peak.
The infrared spectrum of
1-chlorobutane is
unique and the whole, or selected wavenumbers, can be used to
fingerprint its identity, sometimes analysing a mixture
containing 1-chlorobutane or following its change of concentration in a
reaction.
Spectra obtained from a liquid film of 1-chlorobutane. The right-hand part of the of the
infrared spectrum of 1-chlorobutane, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of 1-chlorobutane and most organic compounds. It is due to a
unique set
of complex overlapping vibrations of the atoms of the molecule of
1-chlorobutane.
1-chlorobutane C4H9Cl,
 ,
 ,
For more see
Molecular structure, classification and
naming of
halogenoalkanes (haloalkanes)
Interpretation of
the infrared spectrum of 1-chlorobutane
The most prominent infrared absorption lines of
1-chlorobutane
For 1-chlorobutane you observe infrared C-H stretching vibrations at wavenumbers ~2880 to
3080 cm-1,
and C-H bending vibrations at wavenumbers ~1300 to 1500
cm-1.
These are typical infrared absorptions of molecules
like 1-chlorobutane with alkyl structures in them.
Characteristic groups of C-Cl
stretching vibrations at
wavenumbers ~580 to 780 cm-1
that you expect in halogenoalkane molecules like 1-chlorobutane.
The absence of other specific functional group bands
will show that particular functional group is absent from the
1-chlorobutane
molecular
structure.
Summary of the infrared spectrum of 1-chlorobutane and extra comments
A structured breakdown of the
infrared (IR) spectrum of 1-chlorobutane, tailored for clarity,
exam alignment, and misconception-busting.
Overview: Infrared
spectrum of 1-Chlorobutane
1-Chlorobutane (C4H9Cl)
is a primary alkyl halide, and its IR spectrum reflects:
- Aliphatic hydrocarbon features
(C–H stretches and bends)
- C–Cl bond vibrations
- A distinct fingerprint region
due to complex skeletal vibrations
Prominent Wavenumbers and Assignments
for the infrared spectrum of 1-Chlorobutane
| Wavenumber
(cm⁻¹) |
Bond /
Vibration |
Assignment |
Intensity /
Shape |
| ~2950–2850 |
C–H stretch (sp³) |
Alkyl C–H symmetric/asymmetric stretch |
Medium, sharp |
| ~1470–1450 |
C–H bend (scissoring) |
CH2 deformation |
Medium |
| ~1370–1350 |
C–H bend (methyl) |
CH3 symmetric deformation |
Weak to medium |
| ~720–725 |
C–H rock (long-chain CH2) |
CH2 rocking (often in straight chains) |
Weak |
| ~850–550 |
C–Cl stretch |
Alkyl chloride C–Cl bond vibration |
Medium, sharp |
| ~1500–400 |
Fingerprint region |
Complex skeletal vibrations |
Multiple, overlapping |
Common
Misconceptions about
the infrared spectrum of 1-Chlorobutane
(see also below)
- Mistaking C–Cl for C=C or aromatic
bands: The C–Cl stretch
(~850–550 cm⁻¹) can be misidentified as aromatic C–H bending or C=C
stretches. Remember: 1-chlorobutane is non-aromatic and
saturated.
- Overinterpreting the fingerprint
region: Students often try to
assign every peak. Instead, focus on diagnostic regions and
use the fingerprint region for compound matching, not
functional group identification.
- Expecting a carbonyl peak (~1700
cm⁻¹): There is no C=O
in 1-chlorobutane. Any strong peak in this region is likely
instrumental noise or contamination.
Exam
Tips for questions involving
the infrared spectrum of 1-Chlorobutane
(see also above)
- Highlight the C–Cl stretch:
It’s a key identifier for haloalkanes. Mention its position and intensity.
- Compare with similar compounds:
Use IR spectra of butane or 2-chlorobutane to show how substitution affects
the fingerprint region.
- Use elimination logic: If
no OH (~3200–3600 cm⁻¹) or C=O (~1700 cm⁻¹) is present, rule out alcohols
and carbonyls.
- Don’t ignore weak bands:
Even weak CH₂ rocking (~720 cm⁻¹) can support identification of
straight-chain alkanes.
- Practice with spectra overlays:
Comparing spectra of isomers helps reinforce pattern recognition.
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Comparing
the
infrared, mass, 1H NMR and 13C NMR spectra of the 4
halogenoalkane isomers of C4H9Cl
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 1-chlorobutane, 2-chlorobutane,
1-chloro-2-methylpropane and 2-chloro-2-methylpropane
image sizes. These four molecules are structural
isomers of molecular formula C4H9Cl
and exemplify the infrared, mass, 1H NMR and 13C NMR spectra of
lower aliphatic halogenoalkanes (haloalkanes, alkyl halides,
chloroalkanes, alkyl chlorides). |
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INFRARED SPECTRA
(above):
Apart from the significant differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, there are no other
great striking differences, but each could be identified from
its infrared spectrum. The infrared spectrum of
2-chloro-2-methylpropane is noticeably simpler in the
fingerprint region, perhaps due to
the greater symmetry of the molecule. |
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MASS SPECTRA (above):
Theoretically, all four can give the parent molecular ions of
m/z 92 and 94, but they are all relatively tiny peaks.
2-chlorobutane and 2-chloro-2-methylpropane give a base ion peak
of m/z 57. The base ion peak for 1-chlorobutane is m/z 56 and
that of 1-chloro-2-methylpropane is m/z 43. Each gives different
patterns of pairs of m/z values two mass units apart, in the
peak height ratio of 3:1, if the positive fragment contains a
chlorine atom (35Cl or 37Cl) e.g look for
m/z pairs 49/51, 63/65 and 77/79 in their mass spectra. |
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1H NMR SPECTRA
(above): The 1H NMR spectra of all four molecules give different
integrated proton ratios i.e.1-chlorobutane
four peaks of ratio 3:2:2:2; 2-chlorobutane four peaks of
ratio 3:3:2:1,
1-chloro-2-methylpropane three peaks of ratio 6:2:1 and
2-chloro-2-methylpropane gives just one peak '1' (effectively no ratio
involved), so all four molecular structures can be distinguished from each other by their
1H NMR spectra proton ratios, numbers of peaks and (n+1)
rule splitting patterns. |
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13C NMR SPECTRA
(above): The
13C NMR spectra of the four molecules show various numbers of
carbon-13 chemical environments i.e 1-chlorobutane and
2-chlorobutane show four 13C NMR resonances,
1-chloro-2-methylpropane three 13C NMR resonances and
2-chloro-2-methylpropane only two 13C resonances (3 and 2
chemical environments respectively. Therefore
1-chloro-2-methylpropane and 2-chloro-2-methylpropane can be
distinguished from the other three by their number of resonances
in their 13C NMR spectra, but 1-chlorobutane and 2-chlorobutane
cannot be distinguished from each other from their number of 13C
NMR resonance lines - other data would be required. |
Key words & phrases: image and diagram of the infrared spectrum
of 1-chlorobutane, complete infrared absorption spectrum of 1-chlorobutane, comparative spectra of
1-chlorobutane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
1-chlorobutane,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of 1-chlorobutane, revision of infrared spectroscopy of 1-chlorobutane, fingerprint region analysis of
1-chlorobutane, how to identify 1-chlorobutane from its infrared spectrum, identifying organic
compounds like 1-chlorobutane from their infrared spectrum, how to analyse the
absorption bands in the infrared spectrum of 1-chlorobutane
n-butyl chloride Diagram of absorption of wavenumber
peaks in the infrared spectrum of 1-chlorobutane. Characteristic peak wavenumbers in the infrared
spectrum of 1-chlorobutane. Finger print identification pattern using the infrared
spectrum of 1-chlorobutane. Revision notes on the infrared spectrum of
1-chlorobutane. Matching
and deducing the structure of the 1-chlorobutane molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic
halogenoalkanes haloalkanes alkyl halides alkyl chlorides chloroalkanes, infrared spectra of
1-chlorobutane, an isomer of molecular formula C4H9Cl explaining the
infrared spectrum of 1-chlorobutane How do you interpret the infrared absorption spectrum of
1-chlorobutane How
to interpret the infrared spectrum of 1-chlorobutane Explanatory diagram of the infrared spectrum of the
1-chlorobutane molecule
in terms of its molecular structure.
Listing data of the prominent main wavenumber peaks troughs in the infrared
spectrum of 1-chlorobutane. How to explain the infrared spectrum of
1-chlorobutane. Use of
the infrared spectrum of 1-chlorobutane, identification of
1-chlorobutane from its
infrared spectrum - fingerprint wavenumber pattern to identify the
1-chlorobutane
molecule. The uses of the infrared spectrum of the 1-chlorobutane molecule. The
distinctive features of the infrared spectrum of the 1-chlorobutane molecule
explained. explaining the peaks-trough of the transmittance of the infrared
spectrum of 1-chlorobutane what does the infrared spectrum tell you about the
structure and properties of the 1-chlorobutane molecule? How is
infrared spectrum of 1-chlorobutane used to identify 1-chlorobutane?
Links associated with 1-chlorobutane
The chemistry of HALOGENOALKANES (haloalkanes)
revision notes INDEX
The mass spectrum of 1-chlorobutane
(n-butyl chloride)
The H-1 NMR spectrum of 1-chlorobutane
(n-butyl chloride)
The C-13 NMR
spectrum of 1-chlorobutane
(n-butyl chloride)
Infrared spectroscopy index
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