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Advanced Organic Chemistry: 13C NMR spectrum: 2-bromo-2-methylpropane

Interpreting 13C NMR spectrum: 2-bromo-2-methylpropane (tert-butyl bromide)

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses involving molecular spectroscopy analysing C-13 carbon-13 NMR spectra of 2-bromo-2-methylpropane

See also comparing infrared, mass, 1H NMR & 13C NMR spectra of 4 halogenoalkane isomers of C4H9Br

13C nmr spectrum of 2-bromo-2-methylpropane C4H9Br (CH3)3CBr tert-butyl bromide C13 carbon-13 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-bromo-2-methylpropane here.

2-bromo-2-methylpropane (tert-butyl bromide), C4H9Br, (CH3)3C-Br

Interpreting the C-13 NMR spectrum of 2-bromo-2-methylpropane

As you can see from the diagram above there are 2 different chemical shift lines in the C-13 NMR spectrum of 2-bromo-2-methylpropane indicating 2 different chemical environments of the 4 carbon atoms of 2-bromo-2-methylpropane.

(CH3)3C-Br

(Note the 2 different colours indicating the 2 different chemical environments of the 4 carbon atoms in 2-bromo-2-methylpropane).

13C chemical shifts (a) to (b) on the C-13 NMR spectrum diagram for 2-bromo-2-methylpropane.

(a) (CH3)3C-Br : 13C NMR chemical shift of 36.4 ppm for the three equivalent carbon atoms of the methyl groups due to the symmetry of the 2-bromo-2-methylpropane molecule.

(b) (CH3)3C-Br : 13C NMR chemical shift of 62.5 ppm for the carbon atom attached to the bromine atom (and methyl groups).

The carbon-13 NMR spectra provides direct evidence of 2 different carbon atom environments for the 4 carbon atoms in the 2-bromo-2-methylpropane molecule, deduced from the presence of 2 different 13C NMR chemical shifts (ppm).

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 4 halogenoalkane isomers of C4H9Br

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-bromobutane, 2-bromobutane, 1-bromo-2-methylpropane and 2-bromo-2-methylpropane image sizes.  These four molecules are structural isomers of molecular formula C4H9Br and exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower aliphatic halogenoalkanes (haloalkanes, alkyl halides, bromoalkanes, alkyl bromides).

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.

MASS SPECTRA (above): All four give the parent molecular ions of m/z 136 and 138, but it is only a relatively tiny peak for 2-bromobutane and 2-bromo-2-methylpropane. All four give the base ion peak of m/z 57. All four give prominent peaks for m/z ions 27, 29, 39 and 41 and all give a tiny peak from an ionised iodine atom at m/z 127. They look quite similar to me and lack a clear fingerprint fragmentation pattern. There are small differences in the relative abundances (peak heights) for pairs of ions involving 79Br/81Br isotopes e.g. m/z 93/95, 107/109 and 121/123. 1-bromo-2-methylpropane is the only one of the four to have a prominent peak for the m/z 43 ion.

1H NMR SPECTRA (above): The 1H NMR spectra of all four molecules give different integrated proton ratios i.e.1-bromobutane four peaks of ratio 3:2:2:2; 2-bromobutane four peaks of ratio 3:3:2:1, 1-bromo-2-methylpropane three peaks of ratio 6:2:1 and 2-bromo-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.

13C NMR SPECTRA (above): The 13C NMR spectra of the four molecules show various numbers of carbon-13 chemical environments i.e 1-bromobutane and 2-bromobutane show four 13C NMR resonances, 1-bromo-2-methylpropane three 13C NMR resonances and 2-bromo-2-methylpropane only two 13C resonances. Therefore 1-bromo-2-methylpropane and 2-bromo-2-methylpropane can be distinguished from the other three by their number of resonances in their 13C NMR spectra, but 1-bromobutane and 2-bromobutane cannot be distinguished from each other from their number of 13C NMR resonance lines - other data would be required.

Key words & phrases: C4H9Br (CH3)3CBr Interpreting the C-13 NMR spectra of 2-bromo-2-methylpropane, 13C nmr spectrum of 2-bromo-2-methylpropane, understanding the carbon-13 nmr spectrum of 2-bromo-2-methylpropane, explaining the line pattern in the high resolution C-13 nmr spectra of 2-bromo-2-methylpropane, revising the C-13 nmr spectrum of 2-bromo-2-methylpropane, ppm chemical shifts of the C-13 nmr spectrum of 2-bromo-2-methylpropane, how to construct the diagram of the C-13 nmr spectrum of 2-bromo-2-methylpropane, how to analyse the chemical shifts in the carbon-13 NMR spectrum of 2-bromo-2-methylpropane deducing the chemical environment of all the carbon atoms in 2-bromo-2-methylpropane examining the c13 nmr spectrum of  2-bromo-2-methylpropane analysing the 13C nmr spectrum of 2-bromo-2-methylpropane how do you sketch and interpret the C-13 NMR spectrum of 2-bromo-2-methylpropane interpreting interpretation of the C-13 NMR spectrum of 2-bromo-2-methylpropane assignment of chemical shifts in the 13C NMR spectrum of 2-bromo-2-methylpropane tert-butyl bromide alkyl halide haloalkane alkyl bromide bromoalkane

Molecular structure diagram of the carbon-13 NMR diagram for the 13C NMR spectrum of 2-bromo-2-methylpropane. Deducing the number of different chemical environments of the carbon atoms in the 2-bromo-2-methylpropane molecule from the 13C chemical shifts in the carbon-13 NMR spectrum of 2-bromo-2-methylpropane. Revision notes on the carbon-13 NMR spectrum of 2-bromo-2-methylpropane. Matching and deducing the structure of the 2-bromo-2-methylpropane molecule from its 13C NMR spectrum. Carbon-13 NMR spectroscopy of halogenoalkanes bromoalkanes alkyl bromides, 13C NMR spectra of 2-bromo-2-methylpropane, an isomer of molecular formula C4H9Br


Links associated with 2-bromo-2-methylpropane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

The infrared spectrum of 2-bromo-2-methylpropane (tert-butyl bromide)

The mass spectrum of 2-bromo-2-methylpropane (tert-butyl bromide)

The H-1 NMR spectrum of 2-bromo-2-methylpropane (tert-butyl bromide)

C-13 NMR spectroscopy index

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