Benzhydrilium ions

The N/s values [where log k = s(E + IV)] for several carbanion (nitronate and malonic acid derivatives) nucleophiles have been determined using benzhydrilium ions in MeOH-acetonitrile (9 91 v/v) and compared with the corresponding values in H2O and in DMSO.86 With one exception, CH(CN)2, the nucleophilicity increases from water to MeOH to DMSO by varying amounts. The difference in behaviour is attributed to solvation rather than to the basicity of the anions. 

A benzhydrilium carbocation series with calibrated electrophilicities, E, has been used to determine the nucleophilicity parameters, N and % for a variety of nucleophile-electrophile reactions. For example, benzhydrilium ions (16 examples, 1.48 > >-10.04) were used to evaluate the Lewis basicities of 2-imidazolines and related A-heterocyclic compounds through Mayr s equation log k = Sj N+E)3 The nucleophilicity parameters N and % of the A-heterocycles were determined by measuring the second-order rate constants for the reactions between the benzhydrilium ions and A-heterocycles. The calculated N and % parameters were shown to be useful in accurately predicting the reaction rates between the same A-heterocycles and another set of electrophiles, Michael acceptors. 

The photogenerations of benzhydrilium ions has been the subject of studies. For example, benzhydryl halides were subjected to photolysis and the chemistry was studied by femtosecond to millisecond transient absorption spectroscopy. " The results indicate that radical pairs are initially formed by homolysis of the carbon-halogen bond. 

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