Question

The major product formed when excess of $HCl$ reacts with 2-Butyne?

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

When two molecules of HX (HCl, HBr or HI) add to the alkynes they for geminal dihalides. In geminal dihalides two halogen atoms are attached to the same carbon atom.
Addition of HX on alkynes obeys Markovnikov's rule.
Markovnikov's rule : Negative part of the addendum (adding molecule) gets attached to that doubly bonded C which posses lesser number of hydrogen atoms.

Here, 2- Butyne react with HCl to form 2-Chloro 2-pentene. It react with another mole of HCl to form two different carbocation. Carbocation (i) is stabilised by +R effect of Cl atom. Thus it forms the major product.

Thus compound (a) is the major product of the given reaction.