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Interpreting the
13C 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 C-13 NMR spectrum of 1-bromo-2-chloroethane
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C-13 NMR spectrum of BrCH2CH2Cl
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C-13
NMR spectroscopy - spectra index
Introductory note on the 13C NMR spectrum of 1-bromo-2-methylethane
Students and teachers please note that my explanation of the
carbon-13 NMR spectrum of 1-bromo-2-methylethane is designed for advanced, but
pre-university, chemistry courses.
The description does not involve
the chemical shift δ
spin-spin coupling effects for
1-bromo-2-methylethane and the relative size of the carbon-13
NMR shifts does not give the ratio of the carbon atoms in the
different non-equivalent chemical environments of the
1-bromo-2-methylethane molecule.
The most common solvent used for investigating the
13C
NMR
spectrum of compounds like 1-bromo-2-methylethane, is CDCl3 and other
deuterated solvents.
TMS is the acronym for tetramethylsilane, formula Si(CH3)4,
whose 13C atoms are arbitrarily given a chemical shift of 0.0
ppm. This is the 'standard' in 13C NMR spectroscopy and all other
13C resonances, called chemical shifts, are measured with
respect to the TMS, and depend on the
individual (electronic) chemical environment of the 13C atoms in
an organic molecule, 1-bromo-2-chloroethane here.
1-bromo-2-chloroethane,
C2H4BrCl,
BrCH2CH2Cl
The molecular structure and naming of haloalkanes
Interpreting the C-13 NMR spectrum of 1-bromo-2-chloroethane
As you can see from the diagram above there are
2 different chemical shift lines in the C-13 NMR spectrum of
1-bromo-2-chloroethane
indicating 2 different chemical environments of the 2 carbon
atoms of 1-bromo-2-chloroethane.
BrCH2CH2Cl
(Note the 2 different colours indicating the
2 different chemical environments of the 2 carbon atoms in
1-bromo-2-chloroethane).
13C
chemical shifts
(a) and (b) on the C-13 NMR
spectrum diagram for 1-bromo-2-chloroethane.
Note the greater effect of the
13C chemical
shift of the
carbon atom by the more electronegative chlorine atom - compared to
effect of bromine.
The carbon-13 NMR spectra provides direct evidence of
2 different carbon atom chemical environments for the
2 carbon atoms in the
1-bromo-2-chloroethane molecule,
deduced from the presence of 2 different 13C chemical
shifts (ppm).
Note on being able to differentiate between 1-bromo-2-chloroethane from
1-bromo-1-chloroethane from their C-13 NMR spectra
Both molecules will
give two 13C NMR chemical shifts, but the two values will be
different for
BrCH2CH2Cl
and
CH3CHBrCl
Due to the much
greater electronegativity effect of the two halogen atoms being
attached to the same carbon atom, for 1-bromo-1-chloroethane,
one C-13 peak is likely to have a chemical shift of >43.0 ppm (-CHBrCl)
and the other is likely to be <30.4 (-CH3)
compared to 1-bromo-2-chloroethane.
Summary of the C-13 NMR spectrum
of 1-bromo-2-chloroethane and extra comments
The 13C NMR spectrum of
1-bromo-2-chloroethane (C2H4BrCl)
is a compact but insightful example of how electronegative substituents
influence carbon environments in saturated halogenated alkanes.
Molecular Structure
Overview for the
C-13 NMR spectrum of
1-bromo-2-chloroethane
- Structure: Br-CH2-CH2-Cl
- Two distinct carbon environments:
- CH2-Br
(carbon bonded to bromine)
- CH2-Cl
(carbon bonded to chlorine)
Expected Chemical
Shifts and Origins for
the C-13 NMR spectrum of
1-bromo-2-chloroethane
| Carbon Type |
Environment |
Chemical shift δ (ppm) |
Origin of Shift |
| CH2-Br |
sp³ carbon bonded to Br |
~33-37,
30.4 ppm |
Bromine causes moderate
deshielding due to polarizability and size |
| CH2-Cl |
sp³ carbon bonded to Cl |
~42-47,
43.0 ppm |
Chlorine is more
electronegative → stronger deshielding → downfield shift |
Common
Misconceptions about the
C-13 NMR spectrum of
1-bromo-2-chloroethane
(see also below)
| Misconception |
Clarification |
| "Halogenated carbons
always appear upfield" |
Not true—electronegative
atoms cause deshielding, shifting signals
downfield |
| "Peak intensity reflects
number of carbons" |
In ¹³C NMR,
peak height is not proportional to carbon count |
| "Signal splitting is
always present" |
Most ¹³C spectra
are proton-decoupled, so signals appear as
singlets |
| "Br causes more downfield
shift than Cl" |
Actually, Cl is
more electronegative, so CH2-Cl
appears further downfield |
Exam Tips for
questions involving C-13 NMR spectrum of 1-bromo-2-chloroethane
(see also above)
- Count unique carbon environments:
1-bromo-2-chloroethane has two signals—each CH₂ is
chemically distinct.
- Use electronegativity trends:
More electronegative neighbours → more deshielding → higher δ.
- Ignore peak height:
Focus on number and position of signals, not their
intensity.
- Know typical ranges:
Note the halogen atom causes a shift in the chemical shifts
- Alkyl CH2: 10-50 ppm
- CH2-Cl: ~42-47 ppm
- CH2-Br: ~33-37 ppm
Key words & phrases: C2H4BrCl BrCH2CH2Cl Interpreting the C-13 NMR spectra of
1-bromo-2-chloroethane, C-13 nmr spectrum of 1-bromo-2-chloroethane, understanding the
carbon-13 nmr spectrum of 1-bromo-2-chloroethane, explaining the line pattern in the high
resolution C-13 nmr spectra of 1-bromo-2-chloroethane, revising the C-13 nmr spectrum of
1-bromo-2-chloroethane, ppm
chemical shifts of the C-13 nmr spectrum of 1-bromo-2-chloroethane, how to construct the diagram of
the C-13 nmr spectrum of 1-bromo-2-chloroethane, how to analyse the chemical shifts in the
carbon-13 NMR spectrum of 1-bromo-2-chloroethane deducing the chemical environment of all the
carbon atoms in 1-bromo-2-chloroethane examining the c13 nmr spectrum of
1-bromo-2-chloroethane analysing the
13-c nmr spectrum of 1-bromo-2-chloroethane how do you sketch and interpret the C-13 NMR spectrum
of 1-bromo-2-chloroethane interpreting interpretation of the C-13 NMR spectrum
of 1-bromo-2-chloroethane
assignment of chemical shifts in the 13C
NMR spectrum of 1-bromo-2-chloroethane How do you interpret the chemical shifts of the C-13 NMR spectrum
of 1-bromo-2-chloroethane How to interpret the C-13 NMR spectrum of
1-bromo-2-chloroethane Explanatory diagram of the 13C C-13 carbon-13 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 carbon-13 NMR spectrum of 1-bromo-2-chloroethane. How to explain the C-13 NMR
spectrum of 1-bromo-2-chloroethane. How to deduce the number of different carbon atom
environments in the 1-bromo-2-chloroethane molecule from its carbon-13 NMR spectrum to
help work out the molecular structure of the 1-bromo-2-chloroethane molecule? The uses
and distinctive features of the carbon-13 NMR spectrum of the
1-bromo-2-chloroethane
molecule explained. What do the number and values of the chemical
shifts from the c-13 carbon-13 NMR spectrum tell us about 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 H-1 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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