The reactions of substituted phenolate anions with m-nitrophenyl, p-nitrophenyl, and 3,4-dinitrophenyl formates follow nonlinear Bransted-type correlations that might be taken as evidence for a change in the rate-limiting step of a reaction that proceeds through a tetrahedral addition intermediate. However, the correlation actually represents two different Bronsted lines that are defined by meta-and para-substituted phenolate anions and by meta-and para-substituted o-chlorophenolate anions. A concerted mechanism for both acetyl-and formyl-transfer reactions is supported by the absence of a detectable change in the Bronsted slope at ApK = 0 for the attacking and leaving phenolate anions within each class of Bronsted correlations. Regular increases in the dependence of log k on the pAa of the nucleophile with increasing pAa of the leaving group correspond to a positive interaction coefficient pxy = d/3lg/d(pA"uc) = d/3nuc/5(pAlg). The observation of two different Bronsted lines for the reactions of substituted phenolate anions with phenyl acetates is attributed to a steric effect that decreases the rate of reaction of substituted o-chlorophenolate anions by 25-50%. The reactions of metaand para-substituted phenolate and o-chlorophenolate anions with substituted phenyl acetate esters follow values of /3nlic = 0.53-0.66 and -j5lg = 0.50-0.63. The reactions of meta-and para-substituted phenolate anions with formate esters are ~103 times faster and follow smaller values of j6nuc = 0.43-0.64 and -/3|g = 0.31-0.48. However, the reactions of meta-and para-substituted o-chlorophenolate anions with the same formate esters follow larger values of /3nuc = 0.63-0.90 and -/3,g = 0.46-0.90. The large values of /3nuc and -/Slg for the reactions of substituted o-chlorophenolate anions with formate esters may arise from destabilization by the o-chloro group of a stacking interaction that is present in the transition state for reactions of formate esters, but not acetate esters.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.