Structure and conformational stability of XC(O)OY (X, Y=F and Cl) molecules - ab initio and DFT studies

Molecular structure of both trans and cis conformers of XC(O)OY (X, Y = F a nd Cl) molecules were determined employing ab initio molecular orbital tech nique and density functional theory (DFT) method. Different vibrational cor rection schemes were applied to correct the bond lengths obtained from the ab initio methods. BLYP and B3LYP methods of DFT were used to optimize the molecules. The atomic basis sets 6-311++G (2d,2p) and 6-311+ +G(3df,3pd) we re used for the above methods. Potential energy surface scan was performed for the FC(O)OF molecule at HF/6-31G*, MPU6-31G*, BLYP/6-311++G(2d,2p) and B3LYP/6-311++G(2d,2p) levels of theory, and interconversion barrier from ci s to trans was calculated and these values were found to be 40.06, 42.72, 4 7.02 and 54.01 kJ/mol respectively and for the same, the experimental value was found to be 35 kJ/mol The Delta E (E-cis - E-trans) values were comput ed at HF-CF, electron correlated and DFT methods. The various basis sets fr om a very small size to a very large size i.e., basis sets were used for th e Delta E calculation, Nowek et al. have also reported the Delta E values b oth at ab initio and DFT methods for the FC(O)OF molecule, The complete spe ctrum of Delta E values of the FC(O)OF molecule is now available and it is a suitable testing bed for experiment and theory. The higher basis set of B LYP level of theory reverses the order of conformation. The Delta E values for the FC(O)OF, CIC(O)OF and CIC(O)OCl molecules were obtained at HF, MP2, BLYP and B3LYP levels of theory. The values of BLYP level of theory is not found to be close to the other theoretical values. The DFT parameters such as chemical hardness and chemical potential were used to discuss the confo rmational stability of the molecule. The Fourier decomposition for the rota tional potential energy of the FC(O)OF molecule are studied. (C) 1999 Elsev ier Science B.V. All rights reserved.