INTERMOLECULAR AND INTRAMOLECULAR ENERGY TRANSFER IN GAMMA-IRRADIATED ALKYLBENZENES AND RELATED MIXTURES.
From radiolysis studies of various hydrocarbon mixtures (principally cyclohexane-benzene), intermolecular energy transfer has been proposed to explain deviations of product yields from those expected on the basis of noninteraction of constituents of the mixtures (1, 2). Similarly, intramolecular energy transfer from alkyl group to phenyl group has been proposed to explain low radiolysis product yields from alkylbenzenes (3-5). In this study, hydrogen yields for a series of alkylbenzenes have been measured in an effort to determine the effect of side-chain length on intramolecular energy transfer. These data, in addition to hydrogen yields measured for related twocomponent hydrocarbon systems, provide a basis for comparison of intermolecular and intramolecular energy transfer.
Mechanisms of Protection in Radiolysis of Organic Systems
The addition of relatively small amounts of certain substances to organic systems markedly reduces yields of radiolysis products. Several mechanisms can be invoked to explain this 'protective'' effect. These can be broadly classified into two types: first, a scavenger effect of the additives on free radicals produced from primarily excited and ionized solvent molecules; second, more pertinent to our present interest, an effect of additive on the precursors of the first chemical decomposition. The additive is assumed to provide an alternative path of energy dissipation, e.g., by inducing internal conversion in the excited solvent, by excitation transfer or by negative-ion formation. Benzene may act as a scavenger, but it appears also to exercise a strong protective effect via some form of this second mechanism. In general, part of the effect of typical radical scavengers may also involve the second mechanism. Chemical and physical evidences for various protection processes are reviewed. (auth) 28OO Low concentrations of solutes which have high electron affinities, such as iodine, the alkyl halides and sulfur dioxide have been shown to decrease the hydrogen yield in the gamma irradiation of cyclohexane by about 40%. This decrease in hydrogen yield is believed due to a transfer of energy-more » to the solute probably by an electron capturc ndcchanism. For these solutes at concentrations of the order of 10/sup -2/ mole fraction a number of other observations have been made of direct chemical interaction between the solute and solvent induced by the radiation. Solutions of hydrogen iodide give higher yields of hydrogen than pure cyclohexane. Changes in the radiation chemistry of these systems due to energy transfer effects which are important at higher concentrations appear to be absent at concentrations below 10/sup -4/ mole fraction.« less
Highly enantio- and diastereoselective synthesis of β-methyl-γ-monofluoromethyl-substituted alcohols.
Enanatiopure β-methyl-γ-monofluoromethyl alcohols were prepared from the allylic alkylation between fluorobis(phenylsulfonyl)methane with Morita-Baylis-Hillman carbonates. The reaction was catalyzed by using the Cinchona alkaloid derivative, (DHQD)(2)AQN. The origin of the stereoselectivity was verified by DFT methods. Calculated geometries and relative energies of various transition states strongly support the observed stereoselectivity.