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Advanced Organic Chemistry: Carbon-13 NMR spectrum of 2-iodobutane

Interpreting the Carbon-13 13C NMR 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 C-13 NMR spectra of 2-iodobutane

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

13C nmr spectrum of 2-iodobutane C4H9I CH3CHICH2CH3 analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of sec-butyl iodide 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-iodobutane here.

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

Interpreting the C-13 NMR spectrum of 2-iodobutane

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

CH3-CHI-CH2-CH3

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

13C chemical shifts (a) to (d) on the C-13 NMR spectrum diagram for 2-iodobutane.

(a)  CH3-CHI-CH2-CH3 : 13C NMR chemical shift of 14.2 ppm for the first methyl carbon atom.

(b)  CH3-CHI-CH2-CH3 : 13C NMR chemical shift of 36.0 ppm for the carbon atom attached to the iodine atom.

(c)  CH3-CHI-CH2-CH3 : 13C NMR chemical shift of 32.4 ppm for the carbon atom of the CH2 group.

(d)  CH3-CHI-CH2-CH3 : 13C NMR chemical shift of 28.5 ppm for the carbon atom of end methyl group.

Note the decreasing effect on the 13C chemical shift as the carbon atom is further from the more electronegative iodine atom in 2-iodobutane.

The carbon-13 NMR spectra provides direct evidence of 4 different carbon atom environments for the 4 carbon atoms in the 2-iodobutane 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 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 Interpreting the C-13 NMR spectra of 2-iodobutane, 13C nmr spectrum of 2-iodobutane, understanding the carbon-13 nmr spectrum of 2-iodobutane, explaining the line pattern in the high resolution C-13 nmr spectra of 2-iodobutane, revising the C-13 nmr spectrum of 2-iodobutane, ppm chemical shifts of the C-13 nmr spectrum of 2-iodobutane, how to construct the diagram of the C-13 nmr spectrum of 2-iodobutane, how to analyse the chemical shifts in the carbon-13 NMR spectrum of 2-iodobutane deducing the chemical environment of all the carbon atoms in 2-iodobutane examining the c13 nmr spectrum of  2-iodobutane analysing the 13C nmr spectrum of 2-iodobutane how do you sketch and interpret the C-13 NMR spectrum of 2-iodobutane interpreting interpretation of the C-13 NMR spectrum of 2-iodobutane assignment of chemical shifts in the 13C NMR spectrum of 2-iodobutane type functional group haloalkane halogenoalkane alkyl iodide sec-butyl iodide

Molecular structure diagram of the carbon-13 NMR diagram for the 13C NMR spectrum of 2-iodobutane. Deducing the number of different chemical environments of the carbon atoms in the 2-iodobutane molecule from the 13C chemical shifts in the carbon-13 NMR spectrum of 2-iodobutane. Revision notes on the carbon-13 NMR spectrum of 2-iodobutane. Matching and deducing the structure of the 2-iodobutane molecule from its 13C NMR spectrum. Carbon-13 NMR spectroscopy of halogenoalkanes iodoalkanes, 13C NMR spectra of 2-iodobutane, an isomer of molecular formula C4H9I


Links associated with 2-iodobutane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

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

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

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

C-13 NMR spectroscopy index

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