Abstract
Crystal structures were determined for two compounds, 2-pyridinecarboxaldehydeazine, 1, and biacetylazine, 2. 2-Pyridinecarboxaldehydeazine crystallizes in space group P21/c with a = 10.0487(7) Å, b = 4.6452(7) Å, c = 11.6700(11) Å, β = 91.030(6)°, V = 544.65(10) Å3, Z = 2, R = 0.0345. Biacetylazine crystallizes in space group C2/c with a = 9.879(7) Å, b = 12.409(4) Å, c = 7.950(6) Å, β = 98.44(6)°, V = 964.0(11) Å3, Z = 4, R = 0.0496. Comparison of the imine bond lengths of these and other azine and diimine systems found in the literature suggests that conjugation of imines is better through the carbon−carbon bond than through the nitrogen−nitrogen bond. Semiempirical structural calculations demonstrate that the N−N bond in these azines is rotationally soft, thereby allowing significant twisting at little energy cost. This accounts for the observation that 1 is planar and 2 is not.