Based on data obtained mainly by the verdazyl method, the effects of a solvent on the rates of the heterolyses of 20 substrates (t‐BuCl, t‐BuBr, t‐BuI, 1‐AdBr, 1‐AdI, 1‐AdOTs, 1‐AdOPic, 1‐chloro‐1‐methylcyclopentane, 1‐bromo‐1‐methylcyclopentane, 1‐chloro‐1‐methylcyclohexane, 1‐bromo‐1‐methylcyclohexane, 2‐bromo‐2‐methyladamantane, p‐methoxyneophyl tosylate, 2‐chloro‐2‐phenylpropane, p‐methoxybenzotrichloride, Ph2CCl2, 7α‐bromocholesterol benzoate, 1‐chloro‐1‐phenylethane, Ph2CHBr, 3‐bromocyclohexene) were analyzed in a wide set of protic and aprotic solvents. The heterolysis rate of tertiary substrates decreases with increase in solvent nucleophilicity, but for secondary substrates it does not depend on solvent nucleophilicity. The negative effect of nucleopilic solvation is caused by the solvation of a contact ion pair, which appears before the limiting step. The lack of nucleophilic solvent assistance indicates that a solvent‐separated ion pair of substrates appears after the limiting step. The limiting step involves the interaction of a contact ion pair with a solvent cavity, resulting in the formation of a cavity‐separated ion pair of substrates. Copyright © 2004 John Wiley & Sons, Ltd.

No abstract

A 6-dimensional grand unified theory with the compact space having the topology of a real projective plane, i.e., a 2-sphere with opposite points identified, is considered. The space is locally flat except for two conical singularities where the curvature is concentrated. One supersymmetry is preserved in the effective 4d theory. The unified gauge symmetry, for example SU(5) , is broken only by the non-trivial global topology. In contrast to the Hosotani mechanism, no adjoint Wilson-line modulus associated with this breaking appears. Since, locally, SU(5) remains a good symmetry everywhere, no UV-sensitive threshold corrections arise and SU(5)-violating local operators are forbidden. Doublettriplet splitting can be addressed in the context of a 6d N = 2 super Yang-Mills theory with gauge group SU(6). If this symmetry is first broken to SU(5) at a fixed point and then further reduced to the standard model group in the above non-local way, the two light Higgs doublets of the MSSM are predicted by the group-theoretical and geometrical structure of the model.

No abstract

Additions of LiClO 4 accelerate the heterolysis of Ph 2 CHCl in g-butyrolactone; v = k[Ph 2 CHCl], SN1 mechanism. The salt effect increases with an increase in the electron-acceptor properties of the verdazyl indicator. A superposition of three salt effects (normal, special, and negative special) is observed.Neutral (ammonium and alkali metal) salts strongly and specifically affect the rate of monomolecular heterolysis reactions (SN1, E1, solvolysis) [23 4]. The rate of these reactions is controlled by ionization of the covalent bond, which occurs via successive formation of three ion pairs: contact (I), spacially separated (II), and solvation-separated (III) [5] R3X 76 47 R + X 3 76 47 R + ...X 3 76 47 R + 9Solv9X 3 I II III 76 Reaction products.In the limiting step, ion pair I interacts with a solvent cavity (cavities occupy~10% of the liquid volume [6]). Ion pair II is formed, which rapidly transforms into ion pair III, which, in turn, rapidly yields the reaction products. The free carbocation is formed only in exceptional cases [5], usually in water or in mixtures with a high water content [7].The rate of monomolecular heterolysis is independent of the nucleophile concentration and is described by a first-order kinetic equation v = k [RX].Salts [M + Y 3 ] can both increase and decrease the reaction rate (Fig. 1). The salt effect depends on particular species (cationoid intermediate or covalent substrate) subject to the action of the salt ions or ion pairs. A study of the kinetics and mechanism of monomolecular heterolysis using the verdazyl method [8] showed that, when a salt acts on the covalent substrate, the reaction rate linearly increases with the salt concentration (normal salt effect, Fig. 1, line 1); when ÄÄÄÄÄÄÄÄÄÄÄÄ 1 For communication XXXVIII, see [1].a salt acts on ion pair I of the substrate, the reaction rate initially sharply increases and then flattens out (dk/d[salt] = 0, special salt effect, curve 2). In the first case, the salt catalyzes formation of ion pair I, and in the second case it facilitates formation of ion pair II. Usually a superposition of the normal and special salt effects is observed: The reaction rate initially sharply grows with increasing salt concentration, and then the dependence becomes linear with a smaller slope (curve 3) [3]. When a salt acts on ion pair III or II, the reaction rate first sharply decreases with an increase in the salt concentration and then flattens out (dk/d[salt] = 0, negative special salt effect, curve 4). In this case, the salt catalyzes the external return of 3 k 2 1 4 [Salt] k 0 extr k extr Fig. 1. Salt effect on the heterolysis rate: (1) normal salt effect, (2) special salt effect, (3) superposition of normal and special salt effects, and (4) negative special salt effect; (k extr , k 0 extr ) extrapolated values.