Interpreting the Carbon-13 NMR spectrum of 2-iodopropane

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-iodopropane

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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-iodopropane here.

Interpreting the C-13 NMR spectrum of 2-iodopropane

As you can see from the diagram above there are 2 different chemical shift lines in the C-13 NMR spectrum of 2-iodopropane indicating 2 different chemical environments of the 3 carbon atoms of 2-iodopropane.

CH₃-CHI-CH₃

(Note the 2 different colours indicating the 2 different chemical environments of the 3 carbon atoms in 2-iodopropane).

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

(a) ¹³C NMR chemical shift of 31.2 ppm for the carbon atoms of the methyl groups.

(b) ¹³C NMR chemical shift of 21.1 ppm for the carbon atom of the CH group attached to the iodine atom.

The carbon-13 NMR spectra provides direct evidence of 2 different carbon atom environments for the 3 carbon atoms in the 2-iodopropane molecule, deduced from the presence of only 2 different 13C NMR chemical shifts (ppm).