Density functional theory investigations on boronyl-substituted ethylenes C2H4−m(BO)m (m = 1-4) and acetylenes C2H2−m(BO)m (m = 1, 2)

The geometrical and electronic structures and electron detachment energies of boronyl-substituted ethylenes C2H4−m(BO)m (m = 1-4) and acetylenes C2H2−m(BO)m (m = 1, 2) have been comparatively studied with the corresponding cyano substitutes at density functional theory level. BO boronyl groups are found to serve basically as σ-radicals in these covalent systems, similar to H in hydrocarbons and CN in cyanocarbons. The electron affinities of boronyl dimer (BO)2 and boronyl-substituted ethylenes and acetylenes and the first and second vertical detachment energies of their anions have been predicted for the first time. The thermodynamic quantity changes of carbon boronyls turned out to be parallel with the corresponding values of cyanocarbons. The typical symmetrical stretching frequencies of BO functional groups at about 2000 cm−1 feature the vibrational properties of boronyl compounds. The results obtained in this paper and our previous work [S.-D. Li, C.-Q. Miao, J.-C. Guo, G.-M. Ren, J. Comp. Chem. 26 (2005) 799] complete the Cn(BO)n carbon boronyl series with n = 2-7 and provide more partially BO-substituted ethylene and acetylene species possible to be synthesized in future experiments.