Chapter 14, Problem 14.66P

Interpretation Introduction

Interpretation:

Why an addition product is normally not observed when an alkyne is treated with a peroxyacid in a way similar to the addition of a carbene is to be explained.

Concept introduction:

Alkynes add a carbene across the $\text{π}$ bond like alkenes do. The product in the case of alkynes has a cyclopropene ring in place of the original $\text{π}$ bond. The formation of the ring occurs by replacing the $\text{π}$ bond with two $\text{σ}$ bonds. One of these bonds is formed by the $\text{π}$ electron pair, and the other is formed by the lone pair of carbene carbon.

Alkenes also add a bridging oxygen in a similar way to form an epoxide ring when treated with peroxyacids.

Alkynes, because of their similarity, would also be expected to react with peroxyacids in a similar way.

The stability of the ring formed is expected to be dependent on the nature of the $\text{π}$ system, changing in the order $\text{aromatic }>\text{ nonaromatic }>\text{ antiaromatic}$.