P, Q and R are structural isomers with molecular formula $\text{C}_4\text{H}_8$. In the dark, all three compounds decolourise bromine readily. P and Q show no stereoisomerism, whereas R occurs as a pair of geometrical (cis-trans) isomers. When treated with hot concentrated, acidified potassium manganate(VII), all three compounds give a range of products, as listed in the table. S forms an orange crystalline product with 2,4-dinitrophenylhydrazine reagent, 2,4-DNPH, but gives no reaction with Fehling’s reagent.
(a)[4]
Give the structural formulae for P, Q, R and S in each case.
(b(i))[2]
Explain what the term stereoisomerism means.
(b(ii))[2]
Draw the displayed formulae of the geometrical isomers of R, and name each one.
(c)[2]
State a reagent that could be used to reduce S, and name the organic product of this reduction.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “P is $\mathrm{CH_2=C(CH_3)_2}$” …