(i)     Identify which alcohol gives spectrum 1 and explain your answer by stating which hydrogen atoms in the molecule are responsible for each of the two peaks.

(ii)     Deduce which alcohol gives spectrum 2. Explain which particular hydrogen atoms in the molecule are responsible for the peaks at 0.9 ppm and 3.4 ppm.

(i)     Deduce which two of the alcohols could produce this spectrum and identify the species responsible for the three peaks.

(ii)     The spectrum also shows a significant peak at m/z = 31. Suggest which alcohol is responsible for this spectrum and deduce the species responsible for the peak at m/z = 31.

Explain why the infrared spectra of all four alcohols are very similar.

(i)     (2-)methylpropan-2-ol;

the (H atoms in the three) –CH₃ groups are responsible for the peak at 1.3 ppm (as there are 9 H atoms in the same environment with no H on the adjacent C atom);

the –OH hydrogen atom is responsible for the peak at 2.0 ppm;

Accept explanations with suitable diagram.

(ii)     (2-)methylpropan-1-ol;

the first peak (at 0.9 ppm) is due to the (H atoms in the) two –CH₃ groups

(bonded to the second carbon atom) / (CH₃)₂CHCH₂OH;

the peak at 3.4 ppm is due to the (H atoms in the) –CH₂– group /

(CH₃)₂CHCH₂OH;

Accept explanations with suitable diagram.

(i)     butan-1-ol and butan-2-ol (as they both contain a \(–{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}\) group);

74: \({{\text{M}}^ + }{\text{ / }}{{\text{C}}_{\text{4}}}{{\text{H}}_{{\text{10}}}}{{\text{O}}^ + }{\text{ / C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{H}}^ + }\) and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{CH(OH)CH}}_3^ + \);

59: \({{\text{C}}_{\text{3}}}{{\text{H}}_{\text{7}}}{{\text{O}}^ + }{\text{ / (M}}–{\text{C}}{{\text{H}}_{\text{3}}}{{\text{)}}^ + }{\text{ / C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{H}}^ + }\) and

\({\text{C}}{{\text{H}}_{\text{2}}}{\text{CH(OH)CH}}_3^ + {\text{ / C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{CH(OH}}{{\text{)}}^ + }\);

45: \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{{\text{O}}^ + }{\text{ / (M}}–{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{{\text{)}}^ + }{\text{ / C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{H}}^ + }\) and \({\text{CH(OH)CH}}_3^ + \);

Accept explained answers instead of formulas.

(ii)     butan-1-ol;

\({\text{C}}{{\text{H}}_{\text{2}}}{\text{O}}{{\text{H}}^ + }\) / \({{\text{(M}}–{{\text{C}}_{\text{3}}}{{\text{H}}_{\text{7}}}{\text{)}}^ + }\);

Penalize missing + signs once only in parts (b) (i) and (ii).

they all contain O–H (which will give a broad peak at ca. \({\text{3500 c}}{{\text{m}}^{ - 1}}\));

they all contain C–H (which will absorb at ca. \({\text{3000 c}}{{\text{m}}^{ - 1}}\));

Award [1 max] for same functional groups/bonds.

Most candidates correctly identified the alcohols, but only the better candidates could explain which hydrogen atoms in the molecule were responsible for the peaks. One comment on the G2 forms was surprised by the reference to TMS. However, all \(^{\text{1}}{\text{H}}\,{\text{NMR}}\) spectra have chemical shifts relative to TMS, and no questions were asked about its function.

Many forgot the + charge of the fragments passing through a mass spectrometer and so lost marks.

The similar infrared spectra of the alcohols was often explained in general terms with no reference to the particular bonds present.