A Stabilisation of Organic Cations

It will be obvious that replacement of hydrogen atoms in one or other of the phenyl rings of triphenyl methyl cation (Ph3C+) by electron releasing conjugating substituents such as RO-, R2N-, RS-, aryl, etc. will increase still further the carbocation stability. Hetero atom effects (e.g. from O, N, S) are even more manifest in carbocations having such substituents attached directly to the electron deficient site as in 

A special case of carbocation stability arises where the cation complies with the Hiiekel (4n+2) rule governing aromatic structures. Of these, the best known and most useful is the cycloheptatrienyl cation, more frequently referred to as the tropylium ion. For an informative and wide ranging account of structures, stabilities, properties and reactions of almost every type of carbocation, reference should be made to the series of monographs edited by Olah and Schleyer (18). 

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