diazo compound

diazo compound, any of a class of organic substances that have as part of their molecular structure the characteristic atomic grouping in which R represents a hydrogen atom or any of a large number of organic groups.

The most common diazo compound is diazomethane, a toxic, explosive yellow gas usually prepared as a solution in ether and often used in laboratory procedures for converting carboxylic acids into their methyl esters or into their homologues.