[en] This paper reports that values of the ₁₄N/₁₅N rate constant ratio for methyl transfer to alkyl-substituted pyridines decrease (become more inverse) as CH³X becomes more reactive and may also decrease as the pyridine becomes more reactive. These changes in K¹⁴/K¹⁵ demonstrate increasing selectivity for ₁₅N in preference to ₁₄N as reactivity increases and thus are in violation of the reactivity-selectivity principle. However, these observed changes in K¹⁴/K¹⁵ are consistent with a very recent prediction that such ''anti-Hammond'' effects should result from changes in quantum mechanical mixing of configurations in the transition state and should dominate the more familiar effects of structural perturbations of the free energy surface