Explain why the structural formula of X cannot be:

The $^{\text{1}}{\text{H}}\,{\text{NMR}}$ spectrum of X consists of three peaks. Deduce the structural formula of X and the relative areas under each peak.

absence of peak between 3200–3600 ${\text{c}}{{\text{m}}^{ - 1}}$/above 3000 ${\text{c}}{{\text{m}}^{ - 1}}$/peak for OH;

presence of peak between 1700–1750 ${\text{c}}{{\text{m}}^{ - 1}}$/peak for C=O;

absence of peak between 1610–1680 ${\text{c}}{{\text{m}}^{ - 1}}$ /peak for C=C;

 ;

Accept CH₃CH₂CHO.

3:2:1;

Ignore order

ECF if structure is incorrect only if its NMR spectrum contains three peaks.

Many candidates only gave at least one reason why X cannot be the given formula.

Many gave the correct formula for X, but some could not identify the relative areas under the peaks.