The molecular structure of pyridine in the gas phase determined from electron diffraction, microwave and infrared data and ab-initio force-field calculations

• Published in: Journal of molecular structure 1987, Vol.156 (3), p.315-329
• Main Authors: Pyckhout, W., Horemans, N., Van Alsenoy, C., Geise, H.J., Rankin, D.W.H.
• Format: Article
• Language: English
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/0022-2860(87)87034-5

The gas-phase molecular structure of pyridine was studied by joint analysis of electron diffraction, microwave and infrared data, augmented by vibrational constraints taken from force-field calculations at the 4-21G ab-initio level. Geometrical constraints arising from 4-21G, 4-31G, 4-21GN* and microwave results were tested. The 4-21GN* constraints were significantly better than the others. The range of models that fit all available experimental data was then investigated with respect to the difference between the CNC and NCC valence angles. This resulted in the following best-fitting model ( r g distances, r 0 α angles): NC = 1.344 Å; C 2C 3 = 1.399 Å; C 3C 4 = 1.398 Å; CH (average) = 1.094 Å; CNC = 116.1°; NCC = 124.6°; C 2C 3C 4 = 117.8°; C 3C 4C 5 = 119.1°; NCH = 115.2°. The data suggest that the perturbation resulting from the N atom is primarily in the CNC part of the ring.