Question

The volatile organic compounds (VOCs) produced by decomposing tissue and organs were studied in an effort to identify possible human-specific markers (PLoS ONE 2015 10(9): e0137341.). Of 452 VOCs isolated, six were found to be unique to humans, so this may prove to be a useful tool for forensic chemists trying to determine the source of unidentified remains. There are two doublets in the expected 1H NMR spectrum of the following human-specific VOC. Identify the protons giving rise to each doublet. Identify the two groups of protons that are associated with the two doublets in the spectrum (enter the numbers in ascending order): and

Answer 1

1 and 7

Step-by-step explanation:

You haven't given the NMR spectrum. I assume the VOC is 3-methylbutyl 2-methylbutanoate (below).

The doublets are the isopropyl methyl groups (1) and the 2-methyl group (7)

Group 1 should appear as a 6H doublet (J ≈ 7 Hz) near 0.9 ppm.

Group 7 should appear as a 3H doublet (J ≈ 7 Hz) at about 1.1 ppm (pulled slightly downfield by the carbonyl group).

A simulated NMR spectrum of the CH₃ region is shown below. The triplet in the spectrum is the terminal methyl group (8).