Consider the following reactions:

Which of the following statements is correct about the reactions?

Options

A. The major product of the reactions I and II is an unsaturated hydrocarbon and via E2.
B. The major product of the reactions Ill and IV is the same and produced through `S_N1`.
C. The major product of reactions I and III are unsaturated hydrocarbons via the same mechanism.
D. The major product of the reaction II is optically active compound with inverted configuration.

Answer

D

Explanation

In the given reactions:
(i)The substrate is a `I^@` halide, but the base/nucleophile, t-BuO-, is a strong hindered base. We should expect, therefore, the major product to be by an E2 pathway and the minor product to be by an `S_N2` pathway.
(ii)The reactant (S) -2-bromobutane, is a` 2^@` halide and one in which the leaving group is attached to a chirality centre. The base/nucleophile is HS-, a strong nucleophile buta weak base. We should expect mainly an `S_N2` reaction, causing an inversion of configuration at the chirality centre and producting the (R) stereoisomer
(iii)The base/nucleophile is OH-, strong baseand a strong nucleophile. The substrate is a` 3^@ `halide, therefore,we should not expect an `S_N2` reaction. The major product should be via an E2 reaction. At this higher temperature and in the presence of a strong base, we should not expect an appreciable amount of the `S_N1` solvolysis product
(iv)This is solvolysis, the only base/nucleophile is the solvent,` CH_3OH`, which is a weak base (therefore no E2 reaction) and a poor nucleophile. The substrate is tertiary ( `therefore` no `S_N2` reaction). At this lower temperature, we should expect mainly an `S_N1` pathway leading to A minor product, by an E1 pathway, would be .