Reaction and Mechanism:

The given reaction involves the reaction of HC≡CH with BeH2.

HC≡CH + BeH2 → Product

The reaction mechanism involves the following steps:

1. The BeH2 molecule acts as a Lewis acid and accepts an electron pair from the C≡C triple bond of HC≡CH to form a complex.

HC≡CH + BeH2 → HC≡CHBeH2

2. The complex undergoes a nucleophilic attack by the hydride ion (H^-) present in BeH2.

HC≡CHBeH2 + H^- → HC=CH-BeH3

3. The product obtained is an alkene with a BeH3 group attached to one of its carbon atoms.

Thus, the major product of the given reaction is HC=CH-BeH3.

Explanation:

- The reaction involves the addition of BeH2 to HC≡CH to form an alkene with a BeH3 group attached to one of its carbon atoms.
- The reaction takes place through a mechanism involving the formation of a complex between HC≡CH and BeH2, followed by a nucleophilic attack by the hydride ion present in BeH2.
- The product obtained is an alkene with a BeH3 group attached to one of its carbon atoms.
- The reaction is useful in the synthesis of organoberyllium compounds, which find applications in organic synthesis and catalysis.