Post Hartree-Fock and density functional theory studies on structure and conformational stability of nitrosoethylene and substituted compounds of nitrosoethylene.

Post Hartree-Fock and density functional theory (DFT) methods were used to study the different conformers of nitrosoethylene H-CH=CH-NO, and substituted compounds of the nitrosoethylene R-CH=CH-NO (R = Cl, NH2, N(CH3)2, OH, OCH3). The molecules were optimized at MP2/6-31G* level of theory of ab initio and B3LYP/6-31G* and B3PW91/6-31G* levels of theory of DFT. Special emphasis has been given to the effect of substitution of pi-electron donor groups NH2, N(CH3)2, OH, and OCH3, which play a major role in modifying the geometrical parameters of -N=O group by the electronic transmission effects through the central group -CH=CH-. The ability of DFT methods to predict the bond length adjacent to the atoms having lone pair electrons has been discussed. The conformational stabilities have been studied using the relative energies and DFT parameters such as chemical hardness and chemical potential. The role of intra-molecular hydrogen bond on the equilibrium structure has been discussed. The vibrational spectra for the different conformers of the nitrosoethylene and substituted compounds have been generated using the MP2/6-31G* level of theory.