Question

performing ozonolysis reactions with alkynes produces carboxylic acids, instead of aldehydes or ketones but the methodology is the same. an unknown alkyne with a molecular formula of cnhn-2 gave the following products upon ozonolysis. what is the structure of the starting material?

Answer 1

The starting material must be an alkyne that can produce two moles of glyoxalic acid upon ozonolysis. The only alkyne that fits this description is 1,3-butadiene.

The only possible structural formula for the starting material is:

CH₃(CH₂)₄-C≡C-H

This alkyne is called 1-heptyne.

Here is a diagram of the ozonolysis of 1-heptyne:

CH3(CH2)4C≡CH + O3 → CH3(CH2)4COOH + HOOCCH2COOH

The ozonolysis reaction proceeds in two steps:

The ozone molecule (O₃) adds to the triple bond of the alkyne to form a cyclic ozonide intermediate.

The cyclic ozonide intermediate is then cleaved by water to produce two carboxylic acids.

In the case of 1-heptyne, the ozonolysis reaction produces acetic acid (CH₃COOH) from the cleavage of the first carbon-carbon bond, and propanedioic acid (HOOC-CH₂-COOH) from the cleavage of the second carbon-carbon bond.