THE DIAGNOSIS OF CONCERTED ORGANIC MECHANISMS

the concept of concertedness is paramount in all discussions of reaction mechanisms. The criterion that a concerted mechanism has a single transition state and hence possesses no intermediates enables the unambiguous diagnosis of these mechanisms. This review describes current experimental techniques which provide unequivocal evidence against processes involving intermediates; such techniques therefore indicate concertedness. Contemporary evidence is discussed for reactions, such as displacements at unsaturated centres, not hitherto regarded as capable of supporting concerted mechanisms.