Chemistry 9701 · AS & A Level · 3.2

3.2 — practice question

P, Q, R, S, T, U and V are the seven structural isomers with molecular formula $\text{C}_5\text{H}_{10}\text{O}$ that contain a carbonyl group. P $\text{CH}_3(\text{CH}_2)_3\text{CHO}$ Q $\text{CH}_3\text{CH}_2\text{CH}(\text{CH}_3)\text{CHO}$ R $(\text{CH}_3)_2\text{CHCH}_2\text{CHO}$ S $(\text{CH}_3)_3\text{CCHO}$ T $\text{CH}_3\text{CH}_2\text{CH}_2\text{COCH}_3$ U $\text{CH}_3\text{CH}_2\text{COCH}_2\text{CH}_3$ V $(\text{CH}_3)_2\text{CHCOCH}_3$
(a)[2]

Out of these seven compounds, just one has stereoisomers. Draw three-dimensional diagrams showing the two stereoisomers of this compound.

(b(i))[1]

P, Q, R, S, T, U and V are tested separately with alkaline $\text{I}_2(aq)$, and the mixture is then acidified. Identify the two compounds that give a positive result with alkaline $\text{I}_2(aq)$. ............... and ...............

(b(ii))[2]

Describe the observations when one of the compounds you identified in b(i) is treated with alkaline $\text{I}_2(aq)$, and give the structural formula of the two carbon-containing products formed in this reaction. observations ............... two carbon-containing products ............... and ...............

(c(i))[1]

The proton ($^1\mathrm{H}$) NMR spectra of P, Q, R, S, T, U and V are compared. Identify the only compound that gives a spectrum with two singlets and no other peaks.

(c(ii))[1]

Fig. 7.1 displays the spectrum obtained from one of these compounds. Identify the compound responsible for this spectrum.

(c(iii))[1]

Name the splitting pattern for the peak at $\delta = 1.1$ in Fig. 7.1, and give the reason for this splitting.

(c(iv))[1]

Identify the substance that gives the small peak at $\delta = 0$ in Fig. 7.1.

(d)[2]

The carbon-13 NMR spectra of R, S, T and U are compared. Complete Table 7.1 to state the number of peaks in the spectrum of each compound.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: Q is CH3CH2CH(CH3)CHO

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