Molecular structure and conformational stability of allylisocyanate - post-Hartree-Fock and density functional theory studies

The molecular structure and conformational stability of allylisocyanate (CH 2CHCH2NCO) molecule was studied using the ab initio and DFT methods. The ge ometries of possible conformers, C-gauche (delta = 120 degrees, theta = 0 d egrees) (delta = C=C-C-N and theta = C-C-N=C) and C-cis N-trans (delta = 0 degrees and theta = 180 degrees) were optimized employing HF/6-31G*, MP2/6- 31G* levels of theory of ab initio and BLYP, B3LYP, BPW91 and B3PW91 method s of DFT implementing the atomic basis set 6-311 + G(d,p). The structural a nd physical parameters of the above conformers were discussed with the expe rimental and theoretical values of the related molecules, methylisocyanate and 3-fluoropropene. It has been found that the N=C=O bond angle is not lin ear as the experimental result for both the conformers and the theoretical bond angle is 173 degrees. The rotational potential energy surfaces have be en performed at the HF/6-31G*, and MP2/6-31G* levels of theory. The Fourier decomposition potentials were analysed at the HF/6-31G*, and MP2/6-31G* le vels of theory. The HF/6-31G* level of theory predicted that the C-gauche c onformer is more stable than the C-cis N-trans conformer by 0.41 kJ/mol, bu t the MP2 and DFT methods predicted the C-cis N-trans conformer is found to be more stable than the C-gauche conformer. The calculated chemical hardne ss value at the HF/6-31G* level of theory predicted the C-cis N-trans form is more stable than C-gauche form, whereas the chemical hardness value at t he MP2/6-31G* level of theory favours the slight preference towards the C-g auge conformer. (C) 2000 Elsevier Science B.V. All rights reserved.