Its infrared (IR) spectrum is represented below.

Deduce the bonds responsible for the absorptions labelled I and II.

I:

II:

The $^{\text{1}}{\text{H}}\,{\text{NMR}}$ spectrum recorded showed four peaks with the following chemical shift values (in ppm):

The integration trace for A:B:C:D was found to be 1:1:1:3.

Deduce what information can be obtained about the hydrogen atoms responsible for peak D at 1.2 ppm from the integration trace in the $^{\text{1}}{\text{H}}\,{\text{NMR}}$ spectrum of X.

Deduce the fragments in the mass spectrum which correspond to the following $m{\text{/}}z$ values.

$m{\text{/}}z = 45$:

$m{\text{/}}z = 17$:

$m{\text{/}}z = 15$:

Deduce the structural formula of X.

Y is an isomer of X, which contains the same functional groups. Deduce the structural formula of Y.

(i)     Like X, 3-methylbutanoic acid is also a source of body odour. Deduce the $m{\text{/}}z$ value for the molecular ion peak on the mass spectrum of this compound.

(ii)     Ethyl propanoate (ethyl propionate) is an isomer of 3-methylbutanoic acid. Its $^{\text{1}}{\text{H}}\,{\text{NMR}}$ spectrum consists of four peaks.

Deduce the ratios of the areas under each peak in the $^{\text{1}}{\text{H}}\,{\text{NMR}}$ spectrum of ethyl propanoate. For each peak, deduce the range of chemical shift values (in ppm), using Table 18 of the Data Booklet, and predict the splitting pattern.

I: O–H and II: C=O;

Do not allow CO for C=O.

Allow OH for O–H.

three hydrogens in same (chemical) environment / CH₃/methyl (group);

Award [2] for all three correct, [1] for any two correct.

$m{\text{/}}z = 45$:

${\text{COO}}{{\text{H}}^ + }/{\text{C}}{{\text{O}}_2}{{\text{H}}^ + }/{{\text{C}}_2}{{\text{H}}_5}{{\text{O}}^ + }$;

$m{\text{/}}z = 17$:

${\text{O}}{{\text{H}}^ + }$;

$m{\text{/}}z = 15$:

${\text{CH}}_3^ +$;

Penalize missing + once only.

${\text{C}}{{\text{H}}_{\text{3}}}{\text{CH(OH)COOH}}/{\text{C}}{{\text{H}}_{\text{3}}}{\text{CH(OH)C}}{{\text{O}}_{\text{2}}}{\text{H}}$;

Allow full or condensed structural formula.

${\text{C}}{{\text{H}}_2}{\text{(OH)C}}{{\text{H}}_2}{\text{COOH}}/{\text{HO(C}}{{\text{H}}_2}{{\text{)}}_2}{\text{COH}}$;

Allow full or condensed structural formula.

(i)     102;

(ii)     

Award [3 max] for four correct rows.

Award [2 max] for any two or three correct rows and [1 max] for any correct row.

There were good answers to Q3 but the usual errors were encountered, such as the omission of a positive charge on mass spectrum fragments. Many were able to deduce the structure of the lactic acid although an ether was a common suggestion. It was disappointing to note that many candidates could not provide the correct $m{\text{/}}z$ value for 3-methylbutanoic acid. Candidates found the $^{\text{1}}{\text{H}}\,{\text{NMR}}$ information difficult although most candidates managed to give one line correctly.

There were good answers to Q3 but the usual errors were encountered, such as the omission of a positive charge on mass spectrum fragments. Many were able to deduce the structure of the lactic acid although an ether was a common suggestion. It was disappointing to note that many candidates could not provide the correct $m{\text{/}}z$ value for 3-methylbutanoic acid. Candidates found the $^{\text{1}}{\text{H}}\,{\text{NMR}}$ information difficult although most candidates managed to give one line correctly.

There were good answers to Q3 but the usual errors were encountered, such as the omission of a positive charge on mass spectrum fragments. Many were able to deduce the structure of the lactic acid although an ether was a common suggestion. It was disappointing to note that many candidates could not provide the correct $m{\text{/}}z$ value for 3-methylbutanoic acid. Candidates found the $^{\text{1}}{\text{H}}\,{\text{NMR}}$ information difficult although most candidates managed to give one line correctly.

There were good answers to Q3 but the usual errors were encountered, such as the omission of a positive charge on mass spectrum fragments. Many were able to deduce the structure of the lactic acid although an ether was a common suggestion. It was disappointing to note that many candidates could not provide the correct $m{\text{/}}z$ value for 3-methylbutanoic acid. Candidates found the $^{\text{1}}{\text{H}}\,{\text{NMR}}$ information difficult although most candidates managed to give one line correctly.

There were good answers to Q3 but the usual errors were encountered, such as the omission of a positive charge on mass spectrum fragments. Many were able to deduce the structure of the lactic acid although an ether was a common suggestion. It was disappointing to note that many candidates could not provide the correct $m{\text{/}}z$ value for 3-methylbutanoic acid. Candidates found the $^{\text{1}}{\text{H}}\,{\text{NMR}}$ information difficult although most candidates managed to give one line correctly.

There were good answers to Q3 but the usual errors were encountered, such as the omission of a positive charge on mass spectrum fragments. Many were able to deduce the structure of the lactic acid although an ether was a common suggestion. It was disappointing to note that many candidates could not provide the correct $m{\text{/}}z$ value for 3-methylbutanoic acid. Candidates found the $^{\text{1}}{\text{H}}\,{\text{NMR}}$ information difficult although most candidates managed to give one line correctly.