C3H7Br CH3CHBrCH3 C-13 nmr spectrum of 2-bromopropane analysis of chemical shifts ppm interpretation of 13C chemical shifts ppm of isopropyl bromide C13 13-C nmr doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Carbon-13 NMR spectrum of 2-bromopropane CH₃CHBrCH₃

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Interpreting the 13C NMR spectrum of 2-bromopropane

[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 C-13 proton NMR spectrum of 2-bromopropane [updated Mar 12th 2026 *]

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The chemistry of organic halogen compounds

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C-13 NMR spectroscopy - spectra index

Introductory note on the 13C NMR spectrum of 2-bromopropane

Students and teachers please note that my explanation of the carbon-13 NMR spectrum of 2-bromopropane is designed for advanced, but pre-university, chemistry courses.

The description does not involve the chemical shift δ spin-spin coupling effects for 2-bromopropane 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 2-bromopropane molecule.

The most common solvent used for investigating the 13C NMR spectrum of compounds like 2-bromopropane, is CDCl₃ and other deuterated solvents.

C3H7Br CH3CHBrCH3 C-13 nmr spectrum of 2-bromopropane analysis of chemical shifts ppm interpretation of 13C chemical shifts ppm of isopropyl bromide C13 13-C nmr doc brown's advanced organic chemistry revision notes

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 - 2-bromopropane here.

2-bromopropane, C₃H₇Br, CH₃CHBrCH₃, ,

The molecular structure and naming of haloalkanes

Interpreting the C-13 NMR spectrum of 2-bromopropane (a secondary haloalkane)

As you can see from the diagram above there are 2 different chemical shift lines in the C-13 NMR spectrum of 2-bromopropane indicating 2 different chemical environments of the carbon atoms.

CH₃CHBrCH₃

(Note the 2 different colours indicating the 2 different chemical environments of the 3 carbon atoms in 2-bromopropane).

¹³C chemical shifts (a) to (b) on the C-13 NMR spectrum diagram for 2-bromopropane. Chemical shifts: 28.5 ppm and 45.4 ppm.

The end carbon atoms of the two methyl groups are equivalent to each other - identical chemical environments.

Note the decreasing effect on the chemical shift as the carbon atom is further from the more electronegative bromine atom of 2-bromopropane.

The carbon-13 NMR spectra a provides direct evidence of ? different carbon atom environments for the ? carbon atoms in the 2-bromopropane molecule, deduced from the presence of ? different 13C chemical shifts (ppm).

Summary of the C-13 NMR spectrum of 2-bromopropane and extra comments

The ¹³C NMR spectrum of 2-bromopropane (CH₃–CHBr–CH₃) with clarity, structure, and exam-ready precision.

Molecular Overview of 2-bromopropane with relevance to the C-13 NMR spectrum

Structure: Symmetrical secondary haloalkane
Carbon environments: Only two distinct types due to symmetry
- Two equivalent methyl (CH₃) carbons
- One methine (CHBr) carbon

Chemical Shifts and Origins for the C-13 NMR spectrum of 2-bromopropane

Chemical Shift (δ, ppm)	Carbon Type	Origin	Notes
~28.6, 28.5 ppm	CH₃	Methyl carbons adjacent to CHBr	Equivalent due to symmetry
~45.2, 45.4 ppm	CHBr	Methine carbon bonded to Br	Deshielded by electronegative Br

CH₃CHBrCH₃

These values may vary slightly depending on solvent and concentration, but the relative positions remain consistent.

Common Misconceptions about the C-13 NMR spectrum of 2-bromopropane (see below too)

Expecting three signals: Students may assume three peaks for three carbons. But due to symmetry, only two signals appear.
Misidentifying CHBr shift: Some may expect it to appear upfield (~20 ppm), not accounting for deshielding by bromine.
Confusing CH₃ shifts with other alkyls: Methyl groups adjacent to halogens shift slightly downfield compared to simple alkanes.

Exam Tips for questions involving the C-13 NMR spectrum of 2-bromopropane (see above too)

State the number of signals: “Two signals due to two distinct carbon environments.”
Quote chemical shifts with context: “The peak at ~45 ppm corresponds to the CHBr carbon, deshielded by bromine.”
Mention symmetry explicitly: “The two methyl groups are chemically equivalent, giving a single signal.”
Avoid overinterpreting: Don’t assign peaks to individual methyl groups—they’re indistinguishable in this spectrum.
Use correct terminology: Refer to “methine carbon” or “CHBr” rather than vague terms like “middle carbon.”

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Links associated with 2-bromopropane

The infrared spectrum of 2-bromopropane

The mass spectrum of 2-bromopropane

The H-1 NMR spectrum of 2-bromopropane

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