The equilibrium molecular structure of 2-cyanopyridine from combined analysis of gas-phase electron diffraction and microwave data and results of ab initio calculations

Abstract

The gas-phase electron diffraction study of 2-cyanopyridine was carried out for the first time. Results of ab initio structure calculations performed at the CCSD(T) level of theory agree well with the equilibrium structure determined by the electron diffraction method in combination with vibrational spectroscopy data and microwave rotational constants. The deviations between them are only a few thousandths of A units and a few tenths of degree in the bond lengths and bond angles, respectively. The structure in the solid state is more different from that in the gas phase. The observed discrepancies between these structures are up to 0.02 A and 2° in the bond lengths and bond angles, respectively. The influence of the ortho-, meta-, and para-cyano substituents on the geometry of pyridine ring is discussed. The pyridine ring is noticeably distorted due to cyano substituents. The Cipso–N and/or Cipso–C bond lengths are elongated both in 2-CNP and 4-CNP by 0.004 A in comparison to those in pyridine, whereas the Cipso–C bond lengths are increased by 0.005 and 0.009 A in 3-CNP.