The role of stereoelectronic effects on the side-chain fragmentation of alkylaromatic radical cations. The reactivity of 5-methoxy-2,2-dimethylindan-1-ol radical cation

Abstract

A kinetic and products study of the reaction of 2,2-dimethyl-5-methoxyindan-1-ol ( 1 ) radical cation, in acidic aqueous solution (pH≤4) has been carried out. 1 + undergoes C–H deprotonation as the exclusive reaction with k=4.6×10 4 s −1. The kinetic data have been compared with those obtained for the radical cations of 1-(4-methoxyphenyl)ethanol ( 2 ) and 1-(4-methoxyphenyl)-2,2-dimethyl-1-propanol ( 3 ), suggesting that the deprotonation rate increases when the C–H bond is forced into a conformation where it is almost aligned with the π-system. The conclusion that overlap between the scissile bond and the π-system is an important requisite for the occurrence of bond cleavage is also supported by the results of DFT calculations carried out for 1 + and 3 +.