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Interpreting the 1H NMR spectrum of 2-bromopropane
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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 1H proton NMR spectrum of 2-bromopropane
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1H NMR spectrum of
CH3CHBrCH3
LINKS associated
with 2-bromopropane
The
chemistry of organic halogen compounds
This is a BIG website, please take time to explore it
H-1 proton NMR spectroscopy -
spectra index
Introductory note on the 1H NMR spectra of 2-bromopropane
Students and teachers please note my explanation of the
proton NMR spectrum of 2-bromopropane is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
2-bromopropane are
confined to a proton spin-spin
coupling effects analysed using the n+1 rule for adjacent
non-equivalent proton fields (n is the number of neighbouring
protons in a non-equivalent different chemical environment for the
2-bromopropane molecule).
It is assumed that the integrated intensities of the
1H
NMR δ
chemical shifts give the ratio of the protons in the different
non-equivalent chemical environments of the 2-bromopropane molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like 2-bromopropane, is CDCl3 and other
deuterated solvents to avoid confusion with a 1H NMR
signal, 2D (2H) has a different NMR chemical
shift.
TMS is the acronym for tetramethylsilane, formula Si(CH3)4,
whose protons are arbitrarily given a chemical shift of 0.0 ppm.
This is the 'standard' in 1H NMR spectroscopy and all
other proton resonances, called chemical shifts, are measured
with respect to the TMS, and depend on the
individual (electronic) chemical environment of the hydrogen atoms
in an organic molecule - 2-bromopropane here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of 2-bromopropane represent the peaks of the intensity of
the chemical shifts of (which are often groups of split lines at
high resolution) AND the relative integrated areas under the peaks
gives you the ratio of protons in the different chemical
environments of the 2-bromopropane molecule.
2-bromopropane,
C3H7Br,
CH3CHBrCH3,
 ,
The molecular structure and naming of haloalkanes
Interpreting the
H-1 NMR spectrum of
2-bromopropane
(a secondary haloalkane)
In terms of spin-spin coupling from the possible proton magnetic orientations,
for 2-bromopropane I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. CH3-CH-
For relatively simple molecules, the low
resolution H-1 NMR spectrum of 2-bromopropane is a good starting point
with two peaks in the ratio 6:1.
The hydrogen atoms (protons) of 2-bromopropane occupy
2
different chemical environments so that the low resolution NMR
spectra should show 2 principal peaks of different H-1 NMR chemical shifts (diagram above for
2-bromopropane).
CH3CHBrCH3
Note the proton ratio 6:1 of the 2 colours of the protons
in the 2 chemically different environments
Chemical shifts
(a) to (c) on the H-1 NMR
spectrum diagram for 2-bromopropane.
The two methyl groups are equivalent to each
other.
Although there are 7 hydrogen atoms in the molecule,
there are only 2 possible different chemical
environments for the hydrogen atoms in 2-bromopropane molecule.
The integrated signal proton ratio 6:1 observed
in the high resolution H-1 NMR spectrum, corresponds with
the structural formula of 2-bromopropane.
The high resolution 1H NMR
spectrum of 2-bromopropane
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of 2-bromopropane - since the peak' is at the apex of a band of
H-1 NMR resonances due to spin - spin coupling field splitting effects - see high resolution
notes on 2-bromopropane below.
So, using the chemical shifts and applying the
n+1 rule to
2-bromopropane
and make some predictions using some colour coding! (In problem
solving you work the other way round!)
(a) 1H
Chemical shift 1.31 ppm, methyl protons: CH3CHBrCH3
This resonance is split into a doublet
by the methyl protons (n+1 = 2).
Evidence for the presence of a -CH- group
in the molecule of 2-bromopropane.
All six
protons of the methyl groups in 2-bromopropane occupy
identical chemical environments and cannot cause each
others proton field to be split.
(b) 1H
Chemical shift 3.79 ppm, CH protons :CH3CHBrCH3
This resonance is split into a
1:6:15:20:15:6:1 septet by the methyl protons.
Evidence for the presence of a CH3-C-CH3 grouping
in the molecule of 2-bromopropane (n+6 = 7).
Note the decreasing effect on the chemical shift as the
hydrogen atom is further from the highly more electronegative bromine atom of 2-bromopropane.
Summary of the
1H NMR
spectrum of 2-bromopropane and extra comments
The ¹H NMR spectrum of 2-bromopropane
(CH3–CHBr–CH3) with clarity,
precision, and exam-ready insights.
Molecular Overview of
2-bromopropane of relevance to
the 1H NMR
spectrum of 2-bromopropane
Proton
Chemical Shifts and Integration for
the 1H NMR
spectrum of 2-bromopropane
|
Chemical Shift (δ, ppm) |
Proton
Type |
Origin |
Splitting Pattern |
Integration |
|
~1.7, 1.31
ppm |
CH3 |
Methyl groups
adjacent to CHBr |
Doublet
(n=1) |
6H |
|
~4.2, 3.79
ppm |
CHBr |
Methine proton
adjacent to two CH₃ |
Septet
(n=6) |
1H |
CH3CHBrCH3
Note: Exact shifts may vary slightly
depending on solvent and instrument, but the pattern remains consistent.
Common
Misconceptions
about the 1H NMR
spectrum of 2-bromopropane
(see below too)
-
Mistaking symmetry for fewer peaks:
Some assume only one signal due to symmetry. In fact, there are
two distinct environments.
-
Misidentifying the septet:
Students may not recognize the seven-line multiplet
as a result of coupling with six equivalent protons.
-
Ignoring integration ratios:
The 6:1 ratio is crucial—methyl protons (6H)
versus methine (1H).
-
Expecting a singlet for CH3:
The methyl signal is a doublet, not a singlet,
due to coupling with the CHBr proton.
Exam Tips
for questions involving
the 1H NMR
spectrum of 2-bromopropane
(see above too)
-
Quote both chemical shifts and splitting:
e.g., “The CH₃ protons appear as a doublet at ~1.7 ppm due to
coupling with the CHBr proton.”
-
Use correct terminology: Say
“methine proton” or “CHBr” rather than “middle hydrogen.”
-
Highlight symmetry: “The two
methyl groups are chemically equivalent, giving a single signal
integrating to 6H.”
-
Mention coupling partners: “The
septet at ~4.2 ppm arises from coupling with six equivalent
methyl protons.”
-
Link integration to structure:
“The 6:1 integration ratio confirms the presence of two methyl
groups and one methine proton.”
The splitting pattern from proton
spin-spin coupling effects is analysed using the n+1 rule for
adjacent non-equivalent proton fields (n is the number of
neighbouring protons in a non-equivalent different chemical
environment).
|
Number of directly adjacent protons 1H
causing splitting |
Splitting pattern produced from the
n+1 rule on spin-spin coupling and the theoretical ratio of line intensities |
|
0
means no splitting |
|
|
|
|
|
|
1 |
|
|
|
|
|
|
|
1
creates a doublet |
|
|
|
|
|
1 |
|
1 |
|
|
|
|
|
|
2
creates a triplet |
|
|
|
|
1 |
|
2 |
|
1 |
|
|
|
|
|
3
creates a quartet |
|
|
|
1 |
|
3 |
|
3 |
|
1 |
|
|
|
|
4
creates a quintet |
|
|
1 |
|
4 |
|
6 |
|
4 |
|
1 |
|
|
|
5
creates a sextet |
|
1 |
|
5 |
|
10 |
|
10 |
|
5 |
|
1 |
|
|
6
creates a septet |
1 |
|
6 |
|
15 |
|
20 |
|
15 |
|
6 |
|
1 |
Key words & phrases:
C3H7Br
CH3CHBrCH3 Interpreting the proton H-1 NMR spectra of 2-bromopropane, low resolution & high resolution proton
nmr spectra of 2-bromopropane, H-1 nmr spectrum of 2-bromopropane, understanding the
hydrogen-1 nmr spectrum of 2-bromopropane, explaining the line splitting patterns from
spin-spin coupling in the
high resolution H-1 nmr spectra of 2-bromopropane, revising the H-1 nmr spectrum of
2-bromopropane,
proton nmr of 2-bromopropane, ppm chemical shifts of the H-1 nmr spectrum of
2-bromopropane,
explaining and analyzing spin line splitting in the H-1 nmr spectrum, how
to construct the diagram of the H-1 nmr spectrum of 2-bromopropane, how to work out the
number of chemically different protons in the structure of the 2-bromopropane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of 2-bromopropane using the n+1 rule to explain the spin - spin coupling splitting in the proton nmr spectrum of 2-bromopropane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of 2-bromopropane
examining the 1H nmr spectrum of 2-bromopropane analysing the 1-H nmr spectrum of
2-bromopropane how do you sketch and interpret the H-1 NMR spectrum of
2-bromopropane
interpreting interpretation of the 1H proton spin-spin coupling causing line
splitting in the NMR spectrum of 2-bromopropane
assignment of chemical shifts in the
proton 1H NMR spectrum of 2-bromopropane formula explaining spin-spin coupling for line splitting
of isopropyl bromide How do you interpret the H-1 NMR spectrum of
2-bromopropane How to interpret
the H-1 NMR spectrum of 2-bromopropane Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the 2-bromopropane
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of 2-bromopropane. How to explain the H-1 NMR spectrum of
2-bromopropane. The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the 2-bromopropane molecule. How to work out the molecular
structure of the 2-bromopropane molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the
2-bromopropane
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the 2-bromopropane
molecule? explaining the spin-spin proton coupling effects in the 1H
NMR spectrum of 2-bromopropane. diagram explaining the proton splitting pattern produced from the
n+1 rule and the theoretical ratio of chemical shift and
values of intensities for the proton NMR spectrum lines of 2-bromopropane
Links associated
with
2-bromopropane
The infrared spectrum of
2-bromopropane
The mass spectrum of
2-bromopropane
The C-13 NMR spectrum of
2-bromopropane
The chemistry of HALOGENOALKANES (haloalkanes)
revision notes INDEX
H-1 proton NMR spectroscopy index
(Please
read 8 points at the top of the 1H NMR index page)
ALL SPECTROSCOPY INDEXES
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