Single Crystal X-ray Structures of 2-Pyridinecarboxaldehydeazine and Biacetylazine:  Implications of the Conjugation in Systems with Carbon−Nitrogen Double Bonds

• Published in: Chemistry of materials 1999-02, Vol.11 (2), p.336-340
• Main Authors: Kesslen, Eric C, Euler, William B, Foxman, Bruce M
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Heterocyclic compounds; Organic compounds; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm9805673

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.