Theoretical study of intra-molecular hydrogen bonding in the five-membered ring type of molecular structures

In this work, eight typical sample molecules with the intra-molecular hydrogen bond of the five-membered ring type structures are selected for investigation. Both B3LYP/6-311 + G(2d,p) and B3LYP/6-31G** chosen from GAUSSIAN 94 package were applied to their molecular geometry by geometrical optimization. The semiempirical localized hydrogen bonding analysis method was applied to the most-stable isomers of the above-mentioned eight molecules. In comparison with our former results, it is found that intra-molecular hydrogen bond strength of this set of five-membered ring type of structures is comparably weaker than the related strength of the six-membered ring type of structures. But when we compared the strength of this set with the H ... O relation of intra-COOH four-membered ring cases, all the evidences indicate that the hydrogen bonding of this set is significantly stronger than the H ... O relation of intra-COOH. The various functional groups -COOH, -CHO, OH and CH3, which influence to the strength of intra-molecular hydrogen bonding, are compared and discussed. Most of them give the reasonable explanations. (C) 2000 Elsevier Science B.V. All rights reserved.