CH bond length variations due to the intramolecular environment: a comparison of the results obtained by the method of isolated CH stretching frequencies and by ab initio gradient calculations

Abstract

Two approaches, one experimental and the other theoretical, to the elucidation of CH bond length variation due to the intramolecular environment are compared. The experimental method is based on the concept of isolated CH stretching frequencies while the theoretical method involves the ab initio gradient procedure. Provided molecules of not too dissimilar structure are compared agreement between the two methods is encouragingly satisfactory. The methods are to some extent complementary, the νisCH method being especially applicable to compounds with heavy atoms (e.g. Br, Ge, etc.) and the ab initio method in cases where isotopic frequency data are lacking. The potential applications of this dual technique approach include assessment of the quality of microwave-based geometries, exploration of link between structure and reactivity and prediction of the structure of these basic units in much larger molecules. © 1984.