SUBSTITUENT EFFECTS IN THE SOLVOLYSIS OF BENZYL TOSYLATES

The substituent effect on the rates of solvolysis of substituted benzyl tosylates in acetic acid was analysed based on the Yukawa–Tsuno LArSR equation. Neither the LArSR nor simple σ+ treatment was capable of providing any linear correlation plot for the full range of substituents. The σ+ plot was not simply bilinear but widely scattered, giving a split pattern of parallel curves with significant gaps. Since any mechanistic transition with substituents should bring about a single continuous curve when plotted against an appropriate substituent constant scale, the split σ+ plot is not in line with an interpretation in terms of a mechanistic transition. On the other hand, the LArSR plots with r = 1·3 coalesced into a single smooth curye including the meta correlation curve. A different resonance demand as high as r = 1·3 is required in order to give a smooth single‐curve correlation for the entire substituent range without splitting. For the reactive substituents down to p‐halogens, a sufficiently linear plot can be obtained against a set of substituent constants with r = 1·3 which can be referred to the substituent effect correlation for the kc mechanism of this system. An identical r value was likewise assigned for the kc mechanism of the hydrolysis for a more severely restricted range of activating substituents down to the 4‐MeS‐3‐CN group. Copyright © 1990 John Wiley & Sons Ltd.