N-Methyl chemical shifts in some 2-, 3- and 4-substituted N-methylpyridinium salts

The chemical shifts of the N-methyl group in a series of 2-, 3- and 4-substituted N-methylpyridinium salts have been measured in DMSO solution. The shift is primarily affected by resonance interaction between the substituent and aza group, and the results suggest that the resonance effect from a 2-substituent is at least as great as from the corresponding 4-substituent.