Theoretical study of glyoxylic and pyruvic acids: rotamers and intramolecular hydrogen bonding

Ab initio MP2/6-31G** and density functional theory B3LYP/6-31G** and B3LYP/6-311+G(2d,p) calculations have been carried out to investigate the structures and the intramolecular hydrogen bonding of glyoxylic and pyruvic acids. Four stable rotamers have been investigated in each molecule. At all levels of calculation, structures containing a hydrogen bond between the OH group of one carbon and a carbonyl oxygen of a second carbon are found to be the most stable which is in accordance with experimental results. We also studied the transition states and energy barriers of the rotational isomerization processes with the same ab initio methods. For the purpose of characterizing the intramolecular hydrogen bonding. we applied various types of 'localized hydrogen bonding analysis methods' to rotamers of these two molecules. All the evidence shows that the stability and the C-s symmetry of these two molecules are closely related to their intramolecular hydrogen bonding effect. (C) 7000 Elsevier Science B.V. All rights reserved.