radicals anhydrides compounds imines imides complexes ylides nitrenes acids cations intermediates carbenes ions oxides oxo oxoacids oxonium acyl iminyl carbonyl amine azomethine aminyl esters arene mustards cobalamines carbyne aryl sulfinic silyl vinylic nitrile carboxylic carbene hydrazide amide dyes groups glycoproteins ACI keto acetals betaines hydrazones kephalins azinic epoxides dipolar polyketides