UNSATURATED NEOPENTYL COMPOUNDS . EFFECT OF METHYL SUBSTITUTION ON ACETOLYSIS RATES OF HOMOALLENIC NEOPENTYL-TYPE BROSYLATES

A series of 2,2-dimethyl-3,4-pentadienyl p-bromobenzenesulfonates with methyl substituents at C-3 and/or C-5 have been prepared and their solvolysis rates determined in buffered, anhydrous acetic acid. A Taft-Streitwieser treatment has been used to estimate that homoallenyl participation enhances the reaction rates by factors of 6200-170,000 times, and to deduce that the additional rate increases caused by 3-methyl substitution are due entirely to steric effects. It is suggested that the transition state of the rate-limiting step in each case is of the homoallyl-cyclopropylcarbinyl type with most of the charge concentrated at the vinyl position, C-4. © 1969, American Chemical Society. All rights reserved.