UNUSUAL INFLUENCE OF NITROGEN ON RATES OF ANION FORMATION . HYDROGEN-DEUTERIUM EXCHANGE OF PYRIDINE AND DIAZINES

Rates of hydrogen-deuterium exchange of pyridine (I), pyrimidine (II), pyridazine (III), and pyrazine (IV) in CH3D-CH3ONa at 164.6° were obtained by an nmr method. Relative rates for I at positions 2,6:3,5:4 are 1.0:9.3:12, for II at 2:4,6:5 are 1.0:3.2:48, and for III at 3,6:4,5 are 1.0:14. Log partial rate factors for nitrogen are ortho, 1.31; meta, 2.43; para, 2.46. Activation at a center ortho to nitrogen is less than at a meta or para position. Exhange is believed to take place by simple deprotonation reactions. The unusual acidity pattern may be the result of two reinforcing factors. They are (1) pair-pair electron repulsion between the carbanion and nitrogen and (2) decreased s character in the ortho CH bond associated with an increased endo ring angle. © 1969, American Chemical Society. All rights reserved.