Correlations between Quantum Calculations and the Contribution of Factors Affecting the Structural Stability and Electronic Properties of Vinyl Azide and Vinyl Isocyanate

Abstract

Abstract: The conformational features of vinyl isocyanate (1) and vinyl azide (2) have been analyzed using G4MP2, CCSD(T)/6-311+G**, B3LYP/6-311+G** and LC-ωPBE/6-311+G** theory levels. Published experimental data indicate that the stability of the cis-isomer of vinyl azide (2) is more than the trans-isomer. This is consistent with the findings attained using G4MP2 and LC-ωPBE/6- 311+G** levels, whereas B3LYP/6-311+G** and CCSD (T)/6-311+G** levels provide false energetic outcomes. Natural Bond Orbital (NBO) interpretation is used to interpret the reason for the stability of the cis stereoisomer of compound 2 and the structural features of compound 1. Dipole-dipole interactions, steric effects, and resonance energies on the structural behaviors of compounds 1 and 2 are also investigated using NBO analysis. The results showed that the stability of the cis conformer of compound 2 compared to its trans conformer could be explained using the steric effect (Pauli Exchange Type Repulsion or PETR). Dipole moments of the cis conformer of compound 2 are evaluated experimentally (from Rotational Spectroscopy) and theoretically. The experimental (from Rotational Spectroscopy) and theoretically evaluated dipole moments of trans-conformation of compound 2 are slightly greater than that in cis-conformation, which is in favor of the cis-conformation, while dipoledipole interactions are in favor of the cis-conformation of compound 1. Accordingly, the electrostatic interactions associated with dipole-dipole interactions do not explain the conformational behaviors of compound 1. The stabilization energies related to the delocalization of electrons are in favor of the cis-conformation of compound 1, whereas it has no considerable effect on compound 2’s conformational behavior.