Molozonide is unstable and changes into ozonide on __________________?

When ozone reacts with an alkene, the reaction first forms an unstable intermediate known as molozonide. The process is called ozonolysis, and it occurs in two main steps. In the first step, the ozone molecule adds to the carbon–carbon double bond of the alkene to produce molozonide, which is a cyclic compound containing three oxygen atoms.

Molozonide is highly unstable because of its weak oxygen–oxygen bonds and the strain in its three-membered ring structure. Due to this instability, molozonide does not exist for long and immediately undergoes rearrangement to form a more stable compound known as ozonide. This rearrangement involves the cleavage of the molozonide and recombination of fragments to produce a stable cyclic trioxolane structure.

Ozonides are more stable than molozonides but can still decompose when subjected to certain conditions. In the next step of ozonolysis, ozonides are treated with water, zinc, or other reducing agents to produce smaller organic compounds such as aldehydes, ketones, or carboxylic acids, depending on the reaction conditions.

The entire ozonolysis mechanism provides an important method for identifying the position of double bonds in organic molecules. The rearrangement from molozonide to ozonide is a key part of this mechanism and occurs spontaneously without external reagents.

In summary, molozonide changes into ozonide by rearrangement due to its inherent instability. This reaction is a fundamental concept in organic chemistry and is widely used for structural analysis and synthetic applications involving unsaturated hydrocarbons.