| Citation | Distinguished for the contributions he has made to physical organic chemistry by his elucidation of organic reaction mechanisms. His early examination of the reactions of organo-sulphur compounds developed into a wide-ranging investigation of several types of reaction. These types form a part of the mechanistic foundation of modern organic chemistry. The reaction types which he has studied include additions, eliminations, cyclisations, and ring cleavage reactions. Three major developments may be highlighted. The first comprehensive study of nucleophilic additions to conjugated alkenes was reported in 1967. This pioneering study provided a basis for his subsequent correlation (1967-1978) of a large number of reactions which proceed by a sequence involving elimination followed by addition. A similar approach, based upon kinetic investigations of cyclisation reactions involving intramolecular nucleophilic substitutions, has shown that widely accepted classical generalisations concerning this type of cyclisation reaction are incorrect. The concept of nucleofugality (the tendency of an atom or group to depart with its bonding electron pair) proposed in 1979 has proved to be extremely useful in leading to an understanding of the influence of structure upon heterolytic reactions. The experimental determination of absolute nucleofugality has led to a clear understanding of the role of ring strain in the acceleration of reactions involving cyclic systems. Quantitative results have been obtained which have demonstrated for the first time that widely accepted views on the mechanisms of a number of general types of chemical reaction were incorrect. Novel rationalisations have been proposed on the basis of these new concepts which have been generally accepted. |