KINETICS OF THE REACTIONS OF THE P-METHOXY-SUBSTITUTED BENZHYDRYL CATION WITH VARIOUS ALKENES AND 1,3-DIENES

The kinetic method described in the preceding article has been used to determine the rate constants for the reaction of (p-CH3OC6H4)(C6H5)CH+BCl4 - with 30 alkenes and 1,3-dienes in dichloromethane at –80 to –30 °C. The second-order rate constants, which reflect the rate of attack of (p-CH3OC6H4)(C6H5)CH+ at these π-systems strongly depend on the electron-releasing ability of the substituents at the developing carbenium center (H2C=C(CH3)R: R = H, 9.39 × 10-4; R = vinyl, 15.6; R = CH3, 23.3; R = Ph, 1450; R = cyclopropyl, 5650 L mol-1 s–1 at –70 °C). The steric effects of substituents at this position are of minor importance (H2C=C(CH3)R: R = Me, 23.3; R = Et, 18.4; R = i-Pr, 6.08; R = t-Bu, 1.21 L mol–1 s–1 at –70 °C). Methyl groups at the electrophilically attacked vinylic position usually lower ΔH* and ΔS*, while a uniform effect on the rate constants is not found. © 1990, American Chemical Society. All rights reserved.