Complete determination of the structure of pyridine by microwave spectra

Isotopic mixtures of ordinary pyridine and 2-13C- and 3-13C-pyridine have been prepared and the microwave spectra recorded. For 2-13C- and 3-13C-pyridine, respectively, 12 and 10 transitions (Q- and R-branch lines) were localized, a number of which could be identified by their Stark-effect. For both 13C-species rotational constants of high precision were calculated. These constants together with known rotational constants for ordinary pyridine, 2D-, 3D-, and 4D-pyridine are sufficient for a complete determination of the ten geometrical parameters of the molecule. The interatomic distances in the model finally adopted are: d[NC(2)] = 1.3402, d[C(2)C(3)] = 1.3945, d[C(3)C(4)] = 1.3944, d[C(2)H(2)] = 1.0843, d[C(3)H(3)] = 1.0805, and d[C(4)H(4)] = 1.0773 A. The valence angles in the aromatic ring [starting with the C(6)NC(2) angle] are: 116°50′, 123°53′, 118°32′, and 118°20′. The distances are thought to be correct to ±0.001A.