Hydrogen exchange at ring carbon in azinium cations

3 Hydrogen exchange at ring carbon in azinium cations 

Hydrogen isotope exchange is facile at the a-position in pyridinium salts. 3-Methyl- and 3-cyano-pyridinium methiodides undergo exchange in the order 2 6 4, 5 in 0.01 M NaOD-D20. The relative rates of H-D exchange for the a-, 3- and 7-positions in 1-methylpyridinium chloride are 3400 3 1. 

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