Carbonium ions diphenylmethyl

The selectivity relationship merely expresses the proportionality between intermolecular and intramolecular selectivities in electrophilic substitution, and it is not surprising that these quantities should be related. There are examples of related reactions in which connections between selectivity and reactivity have been demonstrated. For example, the ratio of the rates of reaction with the azide anion and water of the triphenylmethyl, diphenylmethyl and tert-butyl carbonium ions were 2-8x10 , 2-4x10 and 3-9 respectively the selectivities of the ions decrease as the reactivities increase. The existence, under very restricted and closely related conditions, of a relationship between reactivity and selectivity in the reactions mentioned above, does not permit the assumption that a similar relationship holds over the wide range of different electrophilic aromatic substitutions. In these substitution reactions a difficulty arises in defining the concept of reactivity it is not sufficient to assume that the reactivity of an electrophile is related... 

The cited evidence supports the hypothesis that a carbonium ion intermediate can be formed under oxo conditions. The subsequent course of reactions leading to the reduced product is more speculative. With benzhydrol, for example, the diphenylmethyl carbonium ion can be formed from dicobalt octacarbonyl and benzhydrol via the following reactions ... 

Diphenylmethyl bromide allowed to react 5 hrs. at room temp, with triethylamine-borane complex in nitromethane -> diphenylmethane. Y ca. 100%. - The yields depend on the stability of the carbonium ions derived from the halides. Prim, halides can not be reduced by this method. F. e., also in liq. SO2, s. S. Matsumura and N. Tokura, Tetrah. Let. 1968, 4703 with diborane in nitromethane s. Tetrah. Let. 1969, 363. 

Alkylations of aromatic amines can be satisfactorily achieved with stable carbonium ions, even in the presence of high concentrations of mineral or Lewis acid catalysts. The diphenylmethyl and triphenyl-methyl cations have been shown to attack predominantly at the para position of anilines and the prominent features of these re-... 

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