ANALYSIS OF THE PHOSPHORUS LONE-PAIR ORIENTATIONAL EFFECT ON 31P_13C COUPLINGS IN 7-(PHOSPHAMETHYL)NORBORNENE

GUSTAVO A. AUCAR; CLAUDIA G. GIRIBET; MARTÍN RUIZ DE AZÚA; AGUSTÍN C DIZ; RUBÉN H. CONTRERAS

JOURNAL OF MOLECULAR STRUCTURE THEOCHEM

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1988 vol. 164 p. 1 - 15

0166-1280

An IPPP-INDO analysis of P-C couplings is carried out in 7-phosphamethyl) norbornene for the anti and syn conformations. A strong orientational effect of the P lone pair is expected to be responsible for the differences in the coupling values between conformations. Total couplings are decomposed into through-space and through-bond components. Further analysis of the through-space Fermi contact term is carried out by resolving it into contributions given by different "through-space coupling pathways", each pathway being defined by excitations which are amenable to direct analysis using the inner-projected polarization propagator technique. The experimental trends of P-C couplings in both conformations are closely reproduced. The differences between both conformations are found to be ruled by: (i) the orientation of the Plone pair, which is shown to be an efficient means of transmitting the spin information; (ii) the transmission through the C-H rear lobe; and (iii) the orientational effect of the P-C antibonding molecular orbital. From (iii) the important role played by vacant molecular orbitals is also brought to attention.