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

A kinetic and products study of the reaction of 2,2-dimethyl-5-methoxyindan-1-ol (1) radical cation, in acidic aqueous solution (pHless than or equal to4) has been carried out. 1(.+) undergoes C-H deprotonation as the exclusive reaction with k=4.6x10(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 pi-system. The conclusion that overlap between the scissile bond and the pi-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(.+). (C) 2002 Elsevier Science Ltd. All rights reserved.