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Interpreting the
1H NMR spectrum of 1-bromo-2-chloroethane
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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 NMR spectrum of 1-bromo-2-chloroethane
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1H NMR spectrum of BrCH2CH2Cl
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H-1 proton NMR spectroscopy -
spectra index
Introductory note on the 1H NMR spectra of 1-bromo-2-methylethane
Students and teachers please note my explanation of the
proton NMR spectrum of 1-bromo-2-methylethane is designed for advanced, but
pre-university, chemistry courses.
The chemical shift
δ splitting pattern effects for
1-bromo-2-methylethane 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
1-bromo-2-methylethane molecule).
It is assumed that the integrated intensities of the
δ
chemical shifts give the ratio of the protons in the different
non-equivalent chemical environments of the
1-bromo-2-methylethane molecule.
The most common solvent used for investigating the 1H NMR
spectrum of compounds like 1-bromo-2-methylethane, is CDCl3 and other
deuterated solvents to avoid confusion with a 1H NMR
signal, 2D (2H) has a different 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 - 1-bromo-2-chloroethane here.
The chemical shifts quoted in ppm on the diagram of
the H-1 NMR spectrum of 1-bromo-2-chloroethane 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 1-bromo-2-chloroethane molecule.
1-bromo-2-chloroethane,
C2H4BrCl,
BrCH2CH2Cl
The molecular structure and naming of haloalkanes
Interpreting the
H-1 NMR spectrum of 1-bromo-2-chloroethane
In terms of spin-spin coupling from the possible proton magnetic orientations,
for 1-bromo-2-chloroethane I
have only considered the interactions of
non-equivalent protons on adjacent carbon atoms
e.g. here Br-CH2-CH2-Cl.
Theoretically, the four hydrogen atoms (protons) of
1-bromo-2-chloroethane occupy 2
different chemical environments so principal peaks of different
H-1 NMR chemical shifts should be observed.
BrCH2CH2Cl
Note the proton
resonance ratio 2:2 (chemical shifts observed as a 1:1 ratio) of the
2 colours of the protons
in the 2 chemically different environments
Chemical shifts (a) to (b) on the H-1 NMR
spectrum diagram for 1-bromo-2-chloroethane.
The high resolution 1H NMR
spectrum of 1-bromo-2-chloroethane
The ppm quoted on the diagram represent the peak
of resonance intensity for a particular proton group in the
molecule of 1-bromo-2-chloroethane - 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 1-bromo-2-chloroethane below.
However, the two resonances are very close together and you
need very high resolution to the two peak values - I've sketched this on the
diagram above.
But, using the chemical shifts and applying the
n+1 rule to
1-bromo-2-chloroethane
you can make some predictions using some colour coding! (In problem
solving you work the other way round!)
(a) 1H
Chemical shift 2.82 ppm: BrCH2CH2Cl
Both 1H NMR chemical
shifts are very close together (splittings overlap) in
1-brom0-2-chloroethane, and this CH2 proton resonance is
split by the other CH2 protons into a 1:2:1
triplet (n+1 = 3 rule)
Evidence for the presence of a CH2 group
in the molecule of 1-bromo-2-chloroethane
(b) 1H
Chemical shift 2.98 ppm: BrCH2CH2Cl
This CH2 proton resonance is
also split by the other CH2 protons into a
1:2:1 triplet (n+1 = 3 rule)
Evidence for the presence of a 2nd CH2 group
in the molecule of 1-bromo-2-chloroethane, since the
chemical shift is slightly different.
Note the increased effect on the
1H chemical
shift by the more electronegative chlorine atom - compared to the less
electronegative bromine.
The two chemical shifts, and subsequent
splitting into triplets, is caused the bromine and chlorine
atoms creating two different 1H chemical environments for the two sets
of CH2 protons.
Note on being able to differentiate between 1-bromo-2-chloroethane from
1-bromo-1-chloroethane from their 1H NMR spectra
The 1H NMR spectrum of
1-bromo-2-chloroethane BrCH2CH2Cl
As described
above, you expect a proton ratio of
2 : 2 for
two peaks.
From the n+1 rule, both
-CH2- peaks will be split into
1:2:1 triplets by the neighbouring non-equivalent -CH2-
protons.
The 1H NMR spectrum of
1-bromo-1-chloroethane CH3CHBrCl
Here, you expect a
different proton ratio of
3 : 1 for
two peaks.
From the n+1 rule, both
proton peaks will be split, the
-CH3 alkyl group proton peak will be split into a 1:1
doublet by the neighbouring non-equivalent -CH- proton group.
The -CH-
group will be split by the neighbouring non-equivalent -CH3
protons into a 1:3:3:1 quartet.
Due to the
much greater electronegativity effect of the two halogen
atoms attached to the same carbon atom, for
1-bromo-1-chloroethane, one 1H NMR peak (-CHBrCl)
is likely to have a chemical shift of >2.98 ppm and the
other (-CH3)
is likely to be <2.82 ppm compared to
1-bromo-2-chloroethane.
Hence the two
molecules can be differentiated by 1H NMR spectroscopy,
despite them both giving two chemical shifts in their 1H NMR
spectra.
Summary of 1H NMR proton
spectrum of 1-bromo-2-chloroethane
and extra comments
The ¹H NMR spectrum of
1-bromo-2-chloroethane (C2H4BrCl)
is a great example for exploring chemical environments, splitting
patterns, and integration - all highly exam-relevant.
Molecular
Overview for the 1H NMR spectrum of 1-bromo-2-chloroethane
- Structure: Br-CH2-CH2-Cl
- Proton types: Two distinct
CH2 groups, each adjacent to a
different halogen
- Total protons: 4
(2 on each carbon)
Chemical
Shifts and Splitting for the 1H NMR spectrum of 1-bromo-2-chloroethane
|
Proton Type |
Environment |
Chemical Shift (δ, ppm) |
Splitting Pattern |
Integration |
| CH2-Br |
Deshielded by bromine |
~2.98 ppm |
Triplet |
2H |
| CH2-Cl |
Deshielded by chlorine |
~2.82 ppm |
Triplet |
2H |
-
BrCH2CH2Cl
- Triplet splitting
arises from two vicinal protons on the adjacent CH2
group (n+1 rule, n = 2).
- The integration ratio is
2:2, reflecting two protons in each environment.
- Note: Exact chemical shifts may vary slightly depending on
solvent and instrument, but the relative positions and patterns
remain consistent.
Common
Misconceptions about the 1H NMR spectrum of 1-bromo-2-chloroethane
(see also below)
|
Misconception |
Clarification |
| "CH2
groups next to halogens always appear as singlets" |
Not true -
vicinal coupling causes splitting unless
symmetry cancels it |
| "Bromine causes
larger downfield shift than chlorine" |
Actually,
chlorine is more electronegative, but bromine
is more polarizable - so shifts vary |
| "Integration is
always 1:1" |
Integration
reflects number of protons, not symmetry or
splitting |
| "Triplets mean
methyl groups" |
Triplets can
arise from any CH₂ coupled to two equivalent
protons |
Exam Tips
for questions involving the 1H NMR spectrum of 1-bromo-2-chloroethane
(see also above)
- Assign peaks by
environment: Look for
halogen proximity and electronegativity effects.
- Use integration to count
protons: Helps confirm
molecular formula and symmetry (usually done for you).
- Apply n+1 rule carefully:
Only for non-equivalent neighboring protons e.g
Br-CH2-CH2-Cl,
different chemical environments created by the different halogen
atoms, so two different chemical shifts.
- Watch for overlapping
triplets: Similar
chemical shifts may cause peak merging - mention this in analysis -
in this case they are very close together, but predictable ratio of
2:2 from the structure of 1-bromo-2-chloroethane.
- Justify assignments:
Always explain why a peak is a triplet (n+1 rule) or why it appears
downfield (electronegativity effect - not expected pre-university?).
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:
C2H4BrCl BrCH2CH2Cl Interpreting the proton H-1 NMR spectra of
1-bromo-2-chloroethane, low resolution & high resolution proton
nmr spectra of 1-bromo-2-chloroethane, H-1 nmr spectrum of
1-bromo-2-chloroethane, understanding the
hydrogen-1 nmr spectrum of 1-bromo-2-chloroethane, explaining the line splitting patterns from
spin-spin coupling in the
high resolution H-1 nmr spectra of 1-bromo-2-chloroethane, revising the H-1 nmr spectrum of
1-bromo-2-chloroethane,
proton nmr of 1-bromo-2-chloroethane, ppm chemical shifts of the H-1 nmr spectrum of
1-bromo-2-chloroethane,
explaining and analyzing spin line splitting in the H-1 nmr spectrum, how
to construct the diagram of the H-1 nmr spectrum of 1-bromo-2-chloroethane, how to work out the
number of chemically different protons in the structure of the
1-bromo-2-chloroethane organic
molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR
spectrum of 1-bromo-2-chloroethane using the n+1 rule to explain the spin - spin coupling
splitting in the proton nmr spectrum of 1-bromo-2-chloroethane deducing the nature of the protons
from the chemical shifts ppm in the H-1 nmr spectrum of 1-bromo-2-chloroethane
examining the 1H nmr spectrum of 1-bromo-2-chloroethane analysing the 1-H nmr spectrum of
1-bromo-2-chloroethane how do you sketch and interpret the H-1 NMR spectrum of
1-bromo-2-chloroethane
interpreting interpretation of the 1H proton spin-spin coupling causing line
splitting in the NMR spectrum of 1-bromo-2-chloroethane
assignment of chemical shifts in the
proton 1H NMR spectrum of 1-bromo-2-chloroethane formula explaining spin-spin coupling for line splitting How do you interpret the H-1 NMR spectrum of
1-bromo-2-chloroethane How to interpret
the H-1 NMR spectrum of 1-bromo-2-chloroethane Explanatory diagram of the chemical
shifts of the 1H H-1 proton NMR spectrum of the
1-bromo-2-chloroethane
molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the
proton NMR spectrum of 1-bromo-2-chloroethane. How to explain the H-1 NMR spectrum of
1-bromo-2-chloroethane. The chemical shifts and integrated values of the proton ratios in the 1-H NMR
spectrum of the 1-bromo-2-chloroethane molecule. How to work out the molecular
structure of the 1-bromo-2-chloroethane molecule from its proton NMR spectrum. The uses
and distinctive features of the proton NMR spectrum of the
1-bromo-2-chloroethane
molecule explained. What does the H-1 proton NMR spectrum chemical
shifts tell us about the
structure and properties of the 1-bromo-2-chloroethane
molecule?
Links associated
with
1-bromo-2-chloroethane
The infrared
spectrum of 1-bromo-2-chloroethane
The mass
spectrum of 1-bromo-2-chloroethane
The C-13 NMR
spectrum of 1-bromo-2-chloroethane
The
physical properties, hazards and uses of
halogenoalkanes (haloalkanes)
The chemistry of HALOGENOALKANES (haloalkanes)
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H-1 proton NMR spectroscopy index
(Please
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