Chemistry - GOC Question with Solution | TestHub

A less stable alkene releases more heat on hydrogenation.

(A) The cis isomer is less stable (steric strain), so cis-but-2-ene (28.6 kcal/mol) $>$ trans-but-2-ene (27.6). The order given is reversed. Wrong.

(B) Propene (30.1 kcal/mol) has fewer alkyl groups on the $\mathrm{C}=\mathrm{C}$ than trans-but-2-ene (27.6). Correct.

(C) The cumulated diene is the least stable (about 71 kcal/mol for two ${\mathrm{H}}_2$); the conjugated diene is stabilised by delocalisation (about 57). Correct.

(D) Cyclohexene takes one mole of ${\mathrm{H}}_2$ (28.6 kcal/mol); cyclohexa-1,3-diene takes two (55.4). The statement is wrong.

Answer: (B), (C).