Parallel behavior in kinetic and NMR effects: secondary deuterium isotope effects on the alkaline hydrolysis of esters

Abstract

..beta..-Deuterium secondary kinetic isotope effects (..beta..-D KIEs) on the alkaline hydrolysis of the p-nitrophenyl esters of acetic, propanoic, butanoic, and pentanoic acids in pH 10.70, 0.20 M carbonate buffer at 25/sup 0/C tend to increase with increasing chain length of the esters up to the pentanoate. The ..beta..-D KIEs are respectively 0.975 +/- 0.004, 0.960 +/- 0.002, 0.940 +/- 0.001, and 0.948 +/- 0.004. The activation energies of the esterolyses of the isotopically light esters follow a similar pattern, as do the /sup 13/C NMR nuclear shieldings in CDCl/sub 3/ of the isotopically light parent carboxylic acids (20.9, 27.4, 35.9, and 33.8 (ppm)) and /sup 13/C NMR one-bond isotope shifts produced by disubstitution of deuterium for hydrogen at the ..cap alpha..-carbons of the acids (0.45, 0.55, 0.60, and 0.59 (ppm)). Correlation of nuclear shieldings and isotope shifts is known from previous work. The possibility is considered that all of the kinetics-based and NMR relationships are linked through the operation of a common ground-state feature of the ester and acid alkyl chains.