Single Crystal X-ray Structures of 2-Pyridinecarboxaldehydeazine and Biacetylazine: Implications of the Conjugation in Systems with Carbon-Nitrogen Double Bonds
Eric C. Kesslen, William B. Euler, Bruce M. Foxman, Chem. Mater., 1999, 11, 336 – 340
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 suggest 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.