What is a carbene and how is it formed?

A carbene is a molecule containing a carbon atom with two unshared electrons. It is formed by the removal of a leaving group from a precursor molecule.

Carbenes are highly reactive species due to the presence of the two unshared electrons on the carbon atom. They can participate in a variety of reactions, including insertion into C-H bonds, cyclopropanation, and olefin metathesis. Carbenes can be classified as either singlet or triplet, depending on the spin state of the two unshared electrons.

Carbenes can be formed by a variety of methods, including thermal decomposition of diazo compounds, photolysis of diazo compounds, and metal-catalysed decomposition of diazo compounds. Diazo compounds are molecules containing a nitrogen-nitrogen double bond and a leaving group. Upon decomposition, the nitrogen-nitrogen bond is broken, and a carbene is formed.

Carbenes have a wide range of applications in organic synthesis, including the synthesis of natural products and pharmaceuticals. They are also used in materials science, such as in the preparation of polymers and coatings. Despite their reactivity, carbenes can be stabilised by appropriate substituents on the carbon atom, allowing for their isolation and characterisation.