The Microwave Spectrum of 2,6-Difluoropyridine I. Assignment and Complete Structure by DRM Spectroscopy

Abstract

Abstract Double resonance modulated (DRM) microwave spectroscopy has been used for the assignment of the rotation spectrum of 2,6-difluoropyridine, and for the study of 10 non-equivalent isotopic forms of this compound. All 13C and 15N spectra were observed in their natural abundances. From these data the complete structure of 2,6-difluoropyridine has been derived. The geometry of the ring was determined independently in two reference frames. Bond distances (in Å, uncertainties 0.001 Å) an bond angles (in degrees, uncertainty 0.1°) are as follows: N(1)-C(2/6) = 1.3168, C(2/6)-C(3/5) = 1.3767, C(3/5)-C(4) = 1.3941, C(2/6)-F(2/6) = 1.347, C(3/5)-H(3/5) = 1.0795, C(4)-H(4) = 1.0822. Angles: C(2)N(1)C(6) = 115.0, N (1)C(2/6)C(3/5) = 126.5, C (2/6) C (3/5) C (4) = 116.1, C(3)C(4)C(5) = 119.8, N(l)C(2/6)F(2/6) = 114.7, C (2/6) C (3/5) H (3/5) = 120.8 and C (3/5) C (4) H (4) = 120.1. These data represent the first quantitative experimental verification of previously postulated distortions of the pyridine ring under substitution.