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Advanced Organic Chemistry: Infrared spectrum of 2-iodobutane

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Interpreting the infrared spectrum of 2-iodobutane

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-iodobutane

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Infrared spectroscopy - spectra index

See also comparison of the infrared, mass, 1H NMR and 13C NMR spectra of the four isomers of C4H9I

infrared spectrum of 2-iodobutane C4H9I CH3CHICH2CH3 wavenumbers cm-1 functional group detection fingerprint pattern identification of sec-butyl iodide doc brown's advanced organic chemistry revision notes 

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

2-iodobutane (sec-butyl iodide), C4H9I, CH3-CHI-CH2-CH3

Interpretation of the infrared spectrum of 2-iodobutane

The most prominent infrared absorption lines of 2-iodobutane

For 2-iodobutane, the C-H stretching vibration absorptions peak at wavenumbers ~2845 to 2975 cm-1.

C-H bending/deformation vibrations absorption bands peaking at wavenumbers ~1365 to 1470 cm-1.

These two sets of absorption bands are typical of most alkyl structures that you see in compounds like 2-iodobutane.

C-C-C skeletal vibrations from the CH3-CH-CH2-CH2 grouping occur at wavenumbers ~1140 to 1255 cm-1 and 750 to 720 cm-1.

Characteristic groups of C-I stretching vibration absorptions occur at wavenumbers ~600 to 500 cm-1 that you expect in 2-iodobutane.

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

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 4 halogenoalkane isomers of C4H9I

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-iodobutane, 2-iodobutane, 1-iodo-2-methylpropane and 2-iodo-2-methylpropane image sizes.  These four molecules are structural isomers of molecular formula C4H9I and exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower aliphatic halogenoalkanes (haloalkanes, alkyl halides, iodoalkanes, alkyl iodides).

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 ion of m/z 184, but it is only a relatively tiny peak for 2-iodo-2-methylpropane. All four give the base ion peak of m/z 57. All four give prominent peaks for m/z ions 29 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.

1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different proton ratios i.e.1-iodobutane four peaks 3:2:2:2, 2-iodobutane four peaks 3:3:2:1, 1-iodo-2-methylpropane three peaks 6:2:1 and 2-iodo-2-methylpropane 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-iodobutane and 2-iodobutane show four 13C NMR resonances, 1-iodo-2-methylpropane three 13C NMR resonances and 2-iodo-2-methylpropane only two 13C resonances. Therefore 1-iodo-2-methylpropane and 2-iodo-2-methylpropane can be distinguished from the other three by their number of resonances in their 13C NMR spectra, but 1-iodobutane and 2-iodobutane cannot be distinguished from each other from their number of 13C NMR resonance lines - other data would be required.

Key words & phrases: isomer of molecular formula C4H9I CH3CHICH2CH3 CH3CH2CHICH3 image and diagram explaining the infrared spectrum of 2-iodobutane, complete infrared absorption spectrum of 2-iodobutane, comparative spectra of 2-iodobutane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of 2-iodobutane, important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum of 2-iodobutane, revision of infrared spectroscopy of 2-iodobutane, fingerprint region analysis of 2-iodobutane, how to identify 2-iodobutane from its infrared spectrum, identifying organic compounds like 2-iodobutane from their infrared spectrum, how to analyse the absorption bands in the infrared spectrum of 2-iodobutane detection of functional groups in the 2-iodobutane molecule example of the infrared spectrum of a molecule like 2-iodobutane with a functional group  interpreting interpretation of the infrared spectrum of 2-iodobutane shows presence of functional group haloalkane halogenoalkane alkyl iodide sec-butyl iodide Diagram of absorption of wavenumber peaks in the infrared spectrum of 2-iodobutane. Characteristic peak wavenumbers in the infrared spectrum of 2-iodobutane. Finger print identification pattern using the infrared spectrum of 2-iodobutane. Revision notes on the infrared spectrum of 2-iodobutane. Matching and deducing the structure of the 2-iodobutane molecule from  its infrared spectrum. Infrared spectroscopy of aliphatic halogenoalkanes iodoalkanes, infrared spectra of 2-iodobutane, an isomer of molecular formula C4H9I

Links associated with 2-iodobutane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

The mass spectrum of 2-iodobutane (sec-butyl iodide)

The H-1 NMR spectrum of 2-iodobutane (sec-butyl iodide)

The C-13 NMR spectrum of 2-iodobutane (sec-butyl iodide)

Infrared spectroscopy index


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