CONFORMATIONS OF TETRA- AND HEXAHYDROPYRIDAZINES . SLOW RING INVERSION AND SLOW NITROGEN INVERSION

The proton nmr spectra of several tetra- and hexahydropyridazines have been studied as a function of temperature. At low temperatures 1, 12, and 19 show two distinct regions where coalescences occur, indicating that both ring inversion and nitrogen inversion have become slow on the nmr time scale. It is concluded that the preferred conformations of these three compounds have one N-methyl group equatorial and one axial. The barrier to ring inversion is smaller than the barrier to nitrogen inversion. All other compounds studied show only one region of signal coalescence. In the case of 13 and 14, these correspond to nitrogen inversion. 15 appears to prefer a conformation with both N-methyl groups equatorial. The implications of these differences of conformational behavior are discussed. © 1969, American Chemical Society. All rights reserved.