Question
(a) Long chain alkanes such as 4-methylheptane can be ‘cracked’ to produce shorter chain hydrocarbons.
(i) State the conditions necessary for this reaction to take place.
(ii) Suggest the structure of B.
(iii) Compounds C, D and E are isomers with the molecular formula \(C_{5}H_{10}\).
On heating with concentrated acidifi ed \(KMnO_{4}\),
● compound C gives \(CO_{2}\) and compound F \((C_{4}H_{8}O_{2})\),
● D and E each give a 1 : 1 mixture of compounds G \((C_{2}H_{4}O_{2})\) and \(H (C_{3}H_{6}O_{2})\). Suggest structures for compounds C – H.
(iv) Name the type of isomerism shown between D and E.
(b) Propene, \(CH_{3}CH=CH_{2}\), reacts with bromine to give 1,2-dibromopropane.
(i) How is this reaction usually carried out?
(ii) State the type of reaction that is occurring here.
(iii) Draw the mechanism of this reaction, including the structures of any intermediates, and any dipoles, lone pairs and curly arrows to show the movements of electrons.
Answer/Explanation
(a) (i) heat with catalyst or heat with\( Al_2O_3\) /SiO_2 \)
(ii) B is\( CH_3CH_2CH_3 \)
(iii) C is \(CH_2\)=CHCH_2CH_2C_3\) D and E are \(CH_3CH\)= \(CHCH_2CH_3\) (one shown as cis, the other as trans) F is\ (CH_3CH_2CH_2CO_2\)H
G is\( CH_{3}CO_{2}\)H
H is\ (CH_3}CH_{2}CO_{2}H\)
(iv) geometrical or cis-trans or E–Z
(b) (i) No particular conditions or in the dark
(ii) electrophilic addition
