Structural parameters, vibrational spectra and centrifugal distortion constants of F(CN)CNX (X = H, F, Cl, Br) and CH3(Y)CNH (Y = H, CN)

Ab initio calculations with full electron correlation by the perturbation method to second order and hybrid density functional theory calculations by the B3LYP method utilizing a variety of basis sets have been carried out for the F(CN)CNX (X = H, F, Cl, Br) and CH3(Y)CNH (Y = H, CN) molecules. From these calculations, force constants, vibrational frequencies, infrared intensities, Raman activities, depolarization ratios, and structural parameters have been determined and compared to the experimental quantities when available. By combining previously reported rotational constants for F(CN)CNBr with the ab initio MP2/6-311+G(d) predicted parameters, adjusted r0 parameters have been obtained. The structural parameters are: distances (Å) (N−Br) = 1.865(3); (CN) = 1.270(3); (C−F) = 1.327(3); (C−C) = 1.437(3); (CN) = 1.160(3); and angles (°) ∠ BrNC = 114.4(5); ∠ NCF = 127.4(5); ∠ NCC = 119.7(5). These reported parameters have much lower uncertainties than those previously reported from the microwave data. Similar theoretical calculations have been carried out for CH3(Y)CNH (Y = H, CN) and r0 structural parameters have been obtained for both the cis and trans conformers of ethylidenimine, CH3(H)CNH, and for cis iminopyruvonitrile, CH3(CN)CNH utilizing previously reported microwave rotational constants. For CH3(H)CNH the determined r0 heavy atom parameters for the cis [trans] form are: distances (Å) (CN) = 1.276(3) [1.275(3)]; (C−C) = 1.500(3) [1.508(3)]; angles (°) ∠ (HNC) = 109.4(5) [108.8(5)]; ∠ (NCC) = 121.2(5) [127.2(5)]; ∠ (HCC) = 116.2(5) [116.4(5)]. Centrifugal distortion constants have been obtained for all of the molecules from the ab initio predicted force constants and the values are compared to the experimentally determined values when available. The results of these studies are compared to the corresponding quantities of some other similar molecules.