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Thermal Isomerizations of Substituted Benzyl Isocyanides:  Relative Rates Controlled Entirely by Differences in Entropies of Activation

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journal contribution
posted on 04.02.1998 by Sung Soo Kim, Won Jung Choi, Yu Zhu, Jin Hyun Kim
The absolute and relative rates of thermal rearrangments of substituted benzyl isocyanides were obtained at the temperatures between 170 and 230 °C. The relative rates are independent of temperature and exhibit excellent Hammett correlations (ρ+ = −0.24). The temperature studies yielded activation parameters ( and ) and their differential counterparts ( and ). The differential terms were plotted against σ+. The secondary α-deuterium kinetic isotope effects (kD/kH = 1.11) were measured at several temperatures. The rate data can be rationalized with the cyclic TS. The substituent effects on the rates are due to the entropic contributions.