Question

Which of the following is most easily cleaved by HBr:

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

For HBr to be effective as an acid, there should be a proton acceptor site. Only two compounds have an oxygen atom, which can be protonated at least on paper. The hydrocarbons are just too stable to react with HBr. Only the oxirane ring will get cleaved because it is highly reactive due to excessive ring strain. The other heterocyclic compound - called furan - is aromatic and thus the oxygen is actually $s{p}^2$ hybridized. Because of resonance involving (4n+2) $\pi$-electrons, the ring is too stable to react with HBr under normal conditions.