Theoretical studies of conformational changes in the 2,2,5,7,8-pentamethylchroman-6-ol derivatives by PM3 semi-empirical method

摘要

Several aspects of the dynamics in esters of 2,2,5,7,8-pentamethylchroman-6-ol are discussed at PM3 level of theory. Both electrostatic and steric intramolecular forces determine the experimental barrier of motion studied by dynamic ~(13)C NMR spectra of methyl groups at the C_2 atom. An unusual long-distance effect on the angles and bond length in dihydropyran ring associated with the rotation of the ester substituents has been observed. Steric hindrances present in the aromatic ring are mostly dependent on the variation of the atomic charges at oxygen atoms and the length of carbon-oxygen bonds in the carbonyl group.