Intramolecular non-bonded interactions between oxygen and group VIA elements. An ab initio molecular orbital and density functional theory investigation of the structures of HX-CH2-CHO (X = S, Se and Te)
Abstract
Non-bonded interactions between the group VIA elements and oxygen atoms play roles in numerous chemical processes, however, the geometries and energetics of these interactions are not yet well defined. Ab initio molecular orbital and density functional methods have been used to study the potential energy surfaces of the substituted acetaldehydes, HX-CH -CH=O, where X is one of the Group VIA chalcophiles S, Se, or Te. Calculations show that the structure of the lowest energy conformer of each of these acetaldehydes has the X-C-C=O backbone substantially twisted so that the non- bonded X···O distance is greater than the sum of the van der Waals radii of X and O, and also that hydrogen bonding is not significant in these forms. The isomeric forms, HX-CH=CH-OH and HO-CH -CH=X, are higher in energy than the lowest-energy twisted forms of HX-CH -CH=O when X = S, Se or Te. In contrast, the lowest energy conformer of HO-CH -CH=O, where hydrogen bonding is significant, is a compact structure with C(s) symmetry. The conformational preferences of these simple species may provide reference points for inter- and intra-molecular interactions in more complex systems. 2 2 2 2
