Structural Effects in Solvolytic Reactions. 39. Examination of the Ability of the < sup > 13 < /sup > C NMR Shift-σ < sup > C+ < /sup > Correlation for Substituted Benzylic Cations To Accommodate the Highly Electron Donating 5-Coumaranyl Moiety. Evaluation of the Significance of the ρ < sup > C+ < /sup > Values Observed for the Simple Aryldialkyl Carbocations

Abstract

Six 5-coumaranyldialkyl carbocations were prepared from the corresponding alcohols in SbFs/FSO3H/SO2ClF at −78 °C and the 13C NMR shifts for the resulting carbocations were measured at −70 °C. The 5-coumaranyl moiety, with a σC+ value of−2.40, serves as a strong electron donor, even stronger than p-methoxyphenyl, to test the proposed linear relationship between the C+ NMR shifts and the σC+ constants for representative aryldialkyl carbocations. Excellent linear correlations including the 5-coumaranyl moiety were observed. The trends in the variation of the ρC+ values observed for these systems are discussed. © 1982, American Chemical Society. All rights reserved.