Diazomethane

A diazo compund is any class of organic substances that have the characteristic atomic grouping: $R_{2}C=N^{+}=N^{-}$ as a part of their molecular structure. R represents a hydrogen atom or any of a large number of organic groups. The most common diazo compound is diazomethane which is 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.