Hydrogen-Bonded Pyridine N-Oxides

Hydrogen bonding substantially reduces the reactivity of pyridine N-oxide so that o+ values determined for the 2- and 4-positions from solvol- 

1- arylethyl acetates indicates that hydrogen bonding reduces the former reactivity by 0.44 o units. This is not unreasonable since, for example, in trifluoroacetic acid the reactivity of the para-position of anisole is reduced by 0.2 o units as a result of hydrogen bonding (73MI1). 

The value of o for N + OH has been determined as above by comparison of the reactivities of substituted pyridines and benzenes, giving 2.1 (phenoxides) and 2.3 (phenols) [68JCS(P2)866] and these are similar to 

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