No abstract

40) For convenience, the units for k values and for concentrations will be given In the text as cm3 sec-1 and cm-3 rather than cm3 molecule-1 sec-1 and molecule cm-3, respectively.

Enthalpies, entropies, and free energies of sublimation of phenol, 4-bromophenol, 4-formylphenol, and 4-nitrophenol have been evaluated from measurements of the vapour pressures of the solid phenols as a function of temperature. Heats of solution of the phenols in water have been determined calorimetrically and together with solubility data allow calculation of the entropies of solution. Enthalpies, free energies, and entropies of hydration are deduced and are discussed in relation to the effect of 4-substituents on the thermodynamics of ionization of phenol in water. Enthalpies of solution and solvation of the four phenols in methanol have also been measured.THE ionization of a 4-substituted phenol in water is accompanied by an entropy change which is less negative the more electron-withdrawing is the 4-substituent . l y 2 The differences between the entropies of ionization for a

No abstract

No abstract

Photoreduction of fluorenone by dimethylaniline in benzene leads to the 9-hydroxy-9-fluorenyl radical I and the N-methylanilinomethyl radical 11, addition of I1 to the oxygen of ground state fluorenone forming radical 111, and combination and cross combination of radicals I and 111. Hydrolysis of these products leads to fluorenone pinacol, 97 Quantum yields for the photoreduction are at a maximum, -0.8, with the unsubstituted dimethylaniline and with weak electron donating or withdrawing substituents.Very strong electron donation may lead to no photoreduction but to efficient quenching, presumably due to excessive stability of the initially formed charge-transfer complex. Values of k,,, rate constant for charge-transfer interaction of excited fluorenone triplet with the substituted dimethylanilines, have been measured in quenching studies. They vary from 3.2 X lo6 M-l sec-' for thep-CN compound to -lolo M-l sec-' for thep-OEt andp-N(CH& compounds and lead to a linear plot of log k,, us. u values, uf for the strong electron donating substituents, u-for p-CN, with p = -1.96. Photoreductions of Methylene Blue by substituted phenylglycines, of benzophenone by substituted dimethylanilines and benzylamines, and of p-aminobenzophenone by dimethylanilines are discussed. yield, and to high yields of N-methylaniline and formaldehyde. Quantum yields decrease with strong electron donating or withdrawing substituents. t has been p r~p o s e d l -~ that photoreduction by amines I proceeds via rapid charge-transfer type interaction of (1) S. G. Cohen and J. I. Cohen, J. Amer. Chem. SOC., 89,164 (1967); J. Phys. Chem., 72, 3782 (1968). (2) S. G. Cohen and H. M. Chao, J. Amer. Chem. SOC., 90,165 (1968). 141 (1973). excited acceptor with the n electrons of nitrogen, k i r , followed either by spin inversion, charge destruction and quenching, ke, Or hydrogen transfer and electron reorganization, kh, as indicated for reduction of excited nism is consistent with low sensitivity of quantum yield (3) S. G. Cohen, A. Parola, and G. H. Parsons, Jr., Chem. Reo., 73.trip1et compounds in eq a mecha-

The enthalpies of ionization of methanol+water mixtures have been measured calorimetrically and are used to calculate the entropies of autoionization. The enthalpies are analyzed in terms of the separate contributions made by transfer of methanol, water, the proton, hydroxide ions and methoxide ions from water to the mixed solvents. Comparison of the relative acidities of water and methanol in the gas phase and in water shows that in water hydroxide ions are more strongly solvated than methoxide ions. p. 1087.p. 1.

No abstract