The geometry dependence of the spin-spin coupling constants in ethane: a theoretical study

The intramolecular surfaces of the spin-spin coupling constants in ethane h ave been analysed in ab initio calculations at the MCSCF level. The Karplus equation has been modified by including the influence of the C-C and C-H b ond lengths, and the CCH bond angle. The C-C bond length affects the vicina l H-H coupling constant in a wide range of torsion angles, while the influe nce of the other two geometric parameters is largest for the torsion angles near 180 degrees. The one-bond coupling constants are sensitive to bond st retching, while the change of the CCH angle mostly influences the C-C and g eminal H-H coupling constant. The C-H coupling constants exhibit differenti al sensitivity to the changes of C-H bond length. (C) 1999 Elsevier Science B.V. All rights reserved.