The Substituent Effect. XII. Solvolysis of 3′- and 4′-Substituted 1-(4-Biphenylyl)ethyl Chlorides

Rate constants of solvolysis of 3′- and 4′-substituted 1-(4-biphenylyl) ethyl chlorides were measured in 80% (v/v) aqueous acetone. The effect of substituents could be correlated excellently with the LArSR relationship. log k⁄k0=−1.56(σ0+0.84ΔσR+) The ρ and r+ values are smaller than those in the corresponding phenyl system under identical conditions (ρ=−4.95, r+=1.15). The difference of the r+ values is interpreted in terms of twisting of the two phenyls around the pivot bond in biphenyl. The same treatment has been applied successfully to other sets of reactivity data; solvolysis, protodesilylation, alkaline hydrolysis, and piperidinodebromination. The results indicate a consistently reduced effectiveness of pi-electronic transmission in biphenylyl relative to phenyl system in all reactions studied.