2J(Se---Se) couplings in diseleno-substituted alkenylic compounds. A CLOPPA-IPPP analysis

CAVASOTTO, CLAUDIO NORBERTO; GIRIBET, CLAUDIA G.; RUIZ DE AZUA, M.C.; CONTRERAS, R.H.; PEREZ, J.

JOURNAL OF MAGNETIC RESONANCE

ACADEMIC PRESS INC ELSEVIER SCIENCE

Año: 1990 vol. 87 p. 209 - 219

1090-7807

A CLOPPA-IPPP analysis of 2J(Se---Se) couplings in two cyclic diseleno-substituted alkenylic compounds is performed. The total FC, PSO, DSO, and SD components of these couplings are evaluated within the RPA-INDO approximation, and total values are compared to the experimental values. The PSO interaction yields large values in both cases. Particularly, it is the dominant interaction in the cyclic plane compound. For this case, an analysis of the main transmission mechanisms of the SO term is performed in terms of localized molecular orbitals (LMOs) representing chemical functions. It is seen that the coupling is mainly transmitted by the occupied and vacant LMOs associated with the Se atoms. The influence of the sigma-type Se lone pairs is negligible, while the inplane Se lone pairs play an important role. Additivity of pathways is also analyzed: a “direct” and an “indirect” nonadditivity of paths are defined. A high direct nonadditivity is observed. A curious influence of the occupied ð vinylic MO in the indirect nonadditivity is shown. Even though it is known that in several geminal couplings the DSO term yields an important contribution, it has a value of only about 0.01 Hz in the present case.