Whilst the results and internal conclusions of the preceding four papers agree in indicating that in each a substitution of SN1 type is under survey, a comparison of all the results and conclusions reveals a total kinetic pattern sufficiently unprecedented to show that the details of the S N ~ mechanism become sipficantly modified in solvent benzene.We have rates of substitution of a common substrate which do not depend on the concentration of the reagent, but do depend on its nature. In concurrent substitutions, we find evidence of competition for a slowly produced intermediate by thereagents, but withcompetingefficiencies whichdo not follow the rates of their independent substitutions. We have catalysis of inconstant kinetic order by many polar molecules, including molecular reagents, of all the substitutions, whether by anionic or molecular reagents, and the anionic substitutions are catalysed the more strongly; so that, when an anionic and a molecular substitution are run concurrently, an increase in the concentration of the molecular reagent diverts the primary reaction away from substitution by that reagent. We have strong catalysis by non-reacting salts, particularly perchlorate, of the molecular substitutions; and this catalysis is subject to competitive effects, which show that the active catalyst, kinetically indicated to be the simple perchlorate ion, is attacking a slowly formed intermediate; that is, it is intervening after a slow step, and yet it is providing a by-pass to a rate-controlling step. Finally, such catalysis does not apply at all to the anionic substitutions, which, if affected, are anticatalysed by perchlorate.This group of results, from any conventional viewpoint largely a collection of paradoxes, is discussed theoretically. I t is pointed out that the customary mechanistic deductions from the kinetic form, including mass-law retardation, of SN1 substitutions is illogically specialised, and that the logically justified, and more general, deductions would include mechanistic modifications capable of accommodating the relations described. These relations are rationalised on the particular basis that SN1 substitutions in benzene involve two slow, jointly rate-controlling steps, with an intervening fast, productcontrolling step. More precisely, a slow ionisation, not entailing dissociation, is succeeded by a f a s t dipole association, and thereafter by a slow quadrupole rearrangement. The first two steps correspond to the two steps of that more familiar type of S N ~ substitution which prevails in highly solvating solvents; but these steps become modified by the low solvating power of solvent benzene. The modifications render the third step necessary, which therefore owes its existence, and its kinetic sigmficance, to the low solvating power of the solvent. The energetics of the various steps are discussed, and it is shown that the expected energies are physically reasonable, and consistent with experiment.THE immediately preceding four papers, which deal severally with the nucleophilic s...

Bateman, Cooper, and Hughes, J., 1940, 930 (electrophilic catalysis by HC1 of alltyl chloride reactions in aprotic solvents) ; Part LIII, Hughes. Ingold, Patai, and Pocker, 1967, 1206 (stability Qf ClHClion in benzene, the reason for the catalysis).

Triphenylmethane derivatives have been isolated (some in high yield) from the products of condensation of phenols with 0-, m-, and 9-nitrobenzaldehydes. Many of them form molecular compounds with hydrocarbon solvents.

The kinetics are studied of the exchange of chlorine between triphenylmethyl chloride and tetra+butylammonium radiochloride in benzene at 26-46O.In these conditions the reaction is of first order in triphenylmethyl chloride, and of zeroth order in the salt at all concentrations up to saturation.This kinetic form and rate are practically unaffected by added tetra-nbutylammonium perchlorate, which undergoes no stoicheiometric reaction with triphenylmethyl chloride. But the kinetic form is changed, and the initial rate is reduced by added tetra-n-butylammonium azide, which concurrently produces the relatively inert substance, triphenylmethyl azide, though not rapidly enough to preclude observation of the strong initial retardation produced by the salt. This retardation is identified as the kinetic " mass-law effect " in an S,1-type reaction, as described in 1940 for unimolecular solvolysis and for other unimolecular substitutions.The rate of exchange is much increased by added nitromethane or nitrobenzene, without disturbance to the first-order form of the NIB. The initial rate of exchange is considerably increased by added pyridine, or tri-rr-butylamine, though now such a disturbance arises, apparently, from reversible interaction between the triphenylmethyl chloride and the amine. The initial rate of exchange is greatly increased by added methyl alcohol, benzyl alcohol, or phenol, which, as reaction continues, produce some kinetic disturbance arising from the concurrent, relatively slow, formation of an ether. All these catalytic effects, whether by non-reacting polar solutes, such as the nitro-compounds, or by reacting ones, such as the hydroxycompounds, have the common characteristic that, notwithstanding a contrary report by Swain and Kreevoy, they display no integral kinetic order which remains uniform over a significant concentration range. The number and

No abstract