What mechanistic intermediate is used to explain the preference for addition of the Br atom,of HBr,to the internal carbon of a terminal alkyne?

Question

Quizplus · Accepted Answer

The preference for addition of the Br atom of HBr to the internal carbon of a terminal alkyne is best explained by the formation of a more stable secondary vinylic carbocation. The addition of HBr to the terminal alkyne gives an intermediate vinyl cation, which can rearrange to form a more stable carbocation. The secondary carbocation is more stable than the primary carbocation, so the Br prefers to add to the internal carbon, resulting in the formation of the more stable intermediate.

What Mechanistic Intermediate Is Used to Explain the Preference for Addition