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Advanced Organic Chemistry: Infrared spectrum of 2-bromo-2-methylpropane

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Interpreting the infrared 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 infrared spectra of 2-bromo-2-methylpropane

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Infrared spectroscopy - spectra index

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

infrared spectrum of 2-bromo-2-methylpropane C4H9Br (CH3)3CBr tert-butyl bromide doc brown's advanced organic chemistry revision notes 

Spectra obtained from a liquid film of 2-bromo-2-methylpropane. The right-hand part of the of the infrared spectrum of 2-bromo-2-methylpropane, wavenumbers ~1500 to 400 cm-1 is considered the fingerprint region for the identification of 2-bromo-2-methylpropane and most organic compounds. It is due to a unique set of complex overlapping vibrations of the atoms of the molecule of 2-bromo-2-methylpropane.

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

Interpretation of the infrared spectrum of 2-bromo-2-methylpropane

The most prominent infrared absorption lines of 2-bromo-2-methylpropane

C-H stretching vibration absorptions peak at wavenumbers ~2860 to 2975 cm-1.

C-H bending/deformation vibrations absorption bands peaking at wavenumbers ~1370 to 1480 cm-1.

These absorption bands are typical of most molecules incorporating an alkyl structures including 2-bromo-2-methylpropane.

C-C-C skeletal vibrations from the CH3-C-CH3 grouping occur at wavenumbers ~1255 to 1140 cm-1 and ~840 to 790 cm-1.

Characteristic groups of C-Br stretching vibration absorptions at wavenumbers ~750 to 500 cm-1 that you expect in 2-bromo-2-methylpropane.

The absence of other specific functional group bands will show that a particular functional group is absent from the 2-bromo-2-methylpropane molecular structure.

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 image and diagram explaining the infrared spectrum of 2-bromo-2-methylpropane, complete infrared absorption spectrum of 2-bromo-2-methylpropane, comparative spectra of 2-bromo-2-methylpropane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of 2-bromo-2-methylpropane, important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum of 2-bromo-2-methylpropane, revision of infrared spectroscopy of 2-bromo-2-methylpropane, fingerprint region analysis of 2-bromo-2-methylpropane, how to identify 2-bromo-2-methylpropane from its infrared spectrum, identifying organic compounds like 2-bromo-2-methylpropane from their infrared spectrum, how to analyse the absorption bands in the infrared spectrum of 2-bromo-2-methylpropane detection of functional groups in the 2-bromo-2-methylpropane molecule example of the infrared spectrum of a molecule like 2-bromo-2-methylpropane with a functional group  interpreting interpretation of the infrared spectrum of 2-bromo-2-methylpropane shows presence of functional group tert-butyl bromide alkyl halide haloalkane alkyl bromide bromoalkane Diagram of absorption of wavenumber peaks in the infrared spectrum of 2-bromo-2-methylpropane. Characteristic peak wavenumbers in the infrared spectrum of 2-bromo-2-methylpropane. Finger print identification pattern using the infrared spectrum of 2-bromo-2-methylpropane. Revision notes on the infrared spectrum of 2-bromo-2-methylpropane. Matching and deducing the structure of the 2-bromo-2-methylpropane molecule from  its infrared spectrum. Infrared spectroscopy of aliphatic halogenoalkanes bromoalkanes alkyl bromides, infrared spectra of 2-bromo-2-methylpropane, an isomer of molecular formula C4H9Br

Links associated with 2-bromo-2-methylpropanee

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

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

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

The C-13 NMR spectrum of 2-bromo-2-methylpropane (tert-butyl bromide)

Infrared spectroscopy index


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