Secondary isotope effects (IEs) on basicities of various deuterated pyridine isotopologues and of 2, 6-lutidine-2, 6-(CD3) 2 have been accurately measured in aqueous solution by an NMR titration method applicable to a mixture. Deuteration at any position of pyridine increases the basicity, but the IE per deuterium is largest for substitution at the 3-position and smallest for the 2-position, which is closest to the site of N-protonation, smaller even ...
