Stability of carbonium ions. Part 3. The transmission of substituent effects across the fluorene and biphenyl systems

Abstract

The effects of substituents (X) upon the rates of solvolysis of α-(7-X-fluoren-2-yl)benzyl chlorides parallel those of substituents in the corresponding reaction of α-(4-X-fluoren-2-yl)benzyl chlorides, although the former is the more susceptible system. These results are consistent with regarding fluorene as a planar biphenyl structure. Both aromatic systems transmit substituent effects less well than the benzene system, but the relative abilities of substituents to affect the rates of the solvolysis are the, same in all three systems. This suggests that the composite electronic (I,M) contribution of substituents is similar regardless of the system through which it is transmitted, so that there is no evidence of a selective, distance-dependent, dampening of one of the electronic contributors, and hence that both I and M contributions are perhaps substantially developed at, and transmitted from, the aromatic atoms bearing the substituents.