Compound D analysis

The mass spectrum shows the parent ion at m/e 116. This is the relative molecular mass of compound D.

The ir spectrum shows a number of C-H peaks just under 3000 cm^-1. There is a clear C=O absorption at 1740 cm^-1. More careful analysis, using data from the data book, suggests that the peak at 1190 cm^-1 could be due to an ester C-O bond.

The nmr spectrum shows a 3H triplet at d1.2 and 2H quartet at d4.2. This would be consistent with an ethyl group attached to an oxygen atom. The remaining three environments are a 3H triplet at d0.9, a 2H sextuplet (5 adjacent hydrogen atoms) at d1.6 and a 2H triplet at d2.3. This is consistent with a propyl group attached to a carbonyl carbon atom. If you click on the hydrogen atoms in the structure below it will highlight the hydrogen atom nearest neighbours in blue. Remember, that the peak splits into an (n + 1) multiplet, where n is the number of nearest neighbours.

We don't need all this analysis to come up with the answer. We know we have a carbonyl group. The nmr shows there are 12 hydrogen atoms and a further 5 carbon atoms. With a molar mass of 116 there must be an additional oxygen atom. This suggests an ester. The nmr splitting pattern then gives us the arrangement of the alkyl chains, showing that the molecule is ethyl butanoate.

We now check that all the facts fit. We might look for some fragments on the mass spectrum. We would expect to see ethyl (m/e 29) and propyl (m/e 43) chains. Breaking the C-O bond would give fragments of m/e 45 and 71. All these peaks are present. It's worth trying to identify some of the other peaks in the mass spectrum.

The smell might give a clue to the identity of this molecule. Esters often smell fruity, and this one smells of pineapples.