RATES OF METHYL TRANSFERS WITH VARIABLE EQUILIBRIUM CONSTANTS

[摘要] Identity rate constants were measured for the reaction of arylphenylsulfides with arylphenylsulfonium triflates in sulfolane, with the aim of using these as input for the Marcus equation and to find the transition state charge distribution. The rate constant for the reactions of N-methylbenzonitrilium triflate with 4-methylbenzonitrile was estimated. The rate and equilibrium constants were determined for the reaction of several arylmethylselenides with both phenylselenide ion and 4-methoxyphenylselenide ion resulting Hammett $ho$ values of +1.80 and +2.02 respectively. The equilibrium constants for these species produced a Hammett $ho$ value of +4.20. Using the Marcus equation, calculated plots of log k versus log $Ksb{m eq}$ for several different work terms and a constant intrinsic barrier showed only a small amount of curvature over a range of 10$sp{12}$ in equilibrium constant. Thus, a series of reactions over a small range of equilibria will not show any appreciable curvature. Rate constants for the reaction of iodide ion with methyl triflate and with dimethylsulfate were measured by stopped-flow techniques. The experimental rate constants differed by only a small amount from those calculated by the Marcus equation.

[发布机构] Rice University

[效力级别] chemistry