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Advanced Organic Chemistry: Carbon-13 NMR spectrum of 1-bromobutane

Interpreting the Carbon-13 NMR spectrum of 1-bromobutane

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 NMR spectra of 1-bromobutane

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

13C nmr spectrum of 1-bromobutane C4H9Br CH3CH2CH2CH2Br analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of n-butyl iodide 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 - 1-bromobutane here.

1-bromobutane, C4H9Br, CH3CH2CH2CH2Br, CH3-CH2-CH2-CH2-Br

Interpreting the C-13 NMR spectrum of 1-bromobutane

As you can see from the diagram above there are 4 different chemical shift lines in the C-13 NMR spectrum of 1-bromobutane indicating 4 different chemical environments of the 4 carbon atoms of 1-bromobutane.

CH3CH2CH2CH2Br 

(Note the 4 different colours indicating the 4 different chemical environments of the 4 carbon atoms in 1-bromobutane).

13C chemical shifts (a) to (d) on the C-13 NMR spectrum diagram for 1-bromobutane.

(a)  CH3-CH2-CH2-CH2-Br: The 13C NMR chemical shift of 13.2 ppm for the methyl group carbon atom 4.

(b)  CH3-CH2-CH2-CH2-Br: The 13C NMR chemical shift of 21.4 ppm for carbon atom 3 of the CH2 group.

(a)  CH3-CH2-CH2-CH2-Br: The 13C NMR chemical shift of 35.0 ppm for carbon atom 2 of the CH2 group.

(b)  CH3-CH2-CH2-CH2-Br: The 13C NMR chemical shift of 33.4 ppm for carbon atom 1 joined to the bromine atom.

The carbon-13 NMR spectra provides direct evidence of 4 different carbon atom environments for the 4 carbon atoms in the 1-bromobutane molecule, deduced from the presence of 4 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 CH3CH2CH2CH2Br Interpreting the C-13 NMR spectra of 1-bromobutane, C-13 nmr spectrum of 1-bromobutane, understanding the carbon-13 nmr spectrum of 1-bromobutane, explaining the line pattern in the high resolution C-13 nmr spectra of 1-bromobutane, revising the C-13 nmr spectrum of 1-bromobutane, ppm chemical shifts of the C-13 nmr spectrum of 1-bromobutane, how to construct the diagram of the C-13 nmr spectrum of 1-bromobutane, how to analyse the chemical shifts in the carbon-13 NMR spectrum of 1-bromobutane deducing the chemical environment of all the carbon atoms in 1-bromobutane examining the c13 nmr spectrum of  1-bromobutane analysing the 13-c nmr spectrum of 1-bromobutane how do you sketch and interpret the C-13 NMR spectrum of 1-bromobutane interpreting interpretation of the C-13 NMR spectrum of 1-bromobutane assignment of chemical shifts in the 13C NMR spectrum of 1-bromobutane type n-butyl iodide alkyl halide functional group haloalkane halogenoalkane bromoalkane

Stick diagram of the relative abundance of ionised fragments in the fingerprint pattern of the mass spectrum of 1-bromobutane. Table of the m/e m/z values and formula of the ionised fragments in the mass spectrum of 1-bromobutane. The m/e m/z value of the molecular ion peak in the mass spectrum of 1-bromobutane.  The m/e m/z value of the base ion peak in the mass spectrum of 1-bromobutane. Possible examples of equations showing the formation of the ionised fragments in 1-bromobutane. Revision notes on the mass spectrum of 1-bromobutane. Matching and deducing the structure of the 1-bromobutane molecule from its mass spectrum. Mass spectroscopy of aliphatic halogenoalkanes bromoalkanes alkyl bromides, mass spectra of 1-bromobutane, an isomer of molecular formula C4H9Br


Links associated with 1-bromobutane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

The infrared spectrum of 1-bromobutane (n-butyl bromide)

The mass spectrum of 1-bromobutane (n-butyl bromide)

The H-1 NMR spectrum of 1-bromobutane (n-butyl bromide)

C-13 NMR spectroscopy index

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