Question 1

What happens when an alkene undergoes ozonolysis?

Accepted Answer

Ozone adds across the C=C bond and forms a five-membered secondary ozonide intermediate with C-O-O-C-O connectivity. Reductive work-up then cleaves the ozonide so that each former alkene carbon becomes a carbonyl carbon in an aldehyde or ketone.

Question 2

Which work-up reagent is used to obtain aldehydes during ozonolysis?

Accepted Answer

Zinc dust with water or dimethyl sulphide is used for reductive work-up. These conditions prevent further oxidation of aldehydes, while ketones remain unchanged.

Question 3

How can ozonolysis products reveal the position of a double bond?

Accepted Answer

First identify the carbonyl groups in the products, then determine which product carbon atoms were connected through the original C=C bond. Rejoining those carbonyl carbons as C=C helps reconstruct the original alkene.

Question 4

What is formed from a terminal =CH2 group during reductive ozonolysis?

Accepted Answer

A terminal =CH2 group gives formaldehyde, HCHO. This follows from the rule that an alkene carbon bearing hydrogen becomes an aldehyde carbonyl carbon.

Question 5

What changes during oxidative ozonolysis work-up?

Accepted Answer

Hydrogen peroxide oxidizes aldehydes into carboxylic acids. A terminal formaldehyde-derived carbon can pass through formic acid and be oxidized further to carbon dioxide.

Ozonolysis of Alkenes — Find Structure from Carbonyl Products

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