A feature of some \(^{\text{1}}{\text{H}}\,{\text{NMR}}\) spectra is the electron-withdrawing effect of electronegative atoms. These atoms cause nearby protons to produce peaks at higher chemical shift values, often in the range 2.5 to 4.5 ppm.

Consider the \(^{\text{1}}{\text{H}}\,{\text{NMR}}\) spectrum of an unknown compound, D, which has a molecular formula \({{\text{C}}_{\text{4}}}{{\text{H}}_{\text{8}}}{{\text{O}}_{\text{2}}}\) and is known to have an absorption in its IR spectrum corresponding to a C=O absorption.

Use this information and the values in Table 18 of the Data Booklet to deduce the structure of D.

D could be \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{COOC}}{{\text{H}}_{\text{3}}}\) or \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOC}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{3}}}\);

this is because there are 3 peaks / 3:2:3 ratio;

explanation of splitting into a singlet a triplet and a quartet;

methyl propanoate/\({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{COOC}}{{\text{H}}_{\text{3}}}\) is correct isomer because of higher chemical shift value of singlet (3.6 instead of 2.0–2.5);

From part (a) it is clear that proton NMR is poorly understood in some schools. Whilst many candidates could identify the correct structure, few could write a description of how they had obtained it from the information provided. Very few candidates explicitly mentioned that there were 3 peaks or explained how the structure had been determined, especially neglecting to explain the splitting patterns.