INTERPRETACION DEL SIGNO DE LA CONSTANTE DE ACOPLAMIENTO INDIRECTO ENTRE ESPINES NUCLEARES SEGUN EL MODELO CLOPPA

ROSANA LOBAYAN; GUSTAVO A. AUCAR; RUBÉN H. CONTRERAS

FACENA

FACULTAD DE CIENCIAS EXACTAS Y NATURALES Y AGRIMENSURA, UNIVERSIDAD NACIONAL DEL NORDESTE

Lugar: Corrientes; Año: 1996 vol. 12 p. 15 - 32

0325-4216

A new interpretation from the CLOPPA (Contribution from Localized Orbitals within Polarization Propagator Approach) scheme on the electronic origin of the sign of indirect NMR spin spin coupling constants is presented. This model overcomes the deficiencies of previous models like the Dirac vector one, Within the CLOPPA model both the J value and its sign are obtained through the sum of "coupling pathways". Each coupling pathway contributes with a sign which is function only of the relationship between the phases, at the nuclear site. of the localized molecular orbitals ( occupied and vacant) that participate in the virtual excitation. So, the consideration of the relative orientation of the coupled nuclear spins is eliminated, Only the Fermi mechanism is considered here, although it is straightforward the extension to the other ones. Some examples of couplings where the Dirac model do not reproduce the experimental sign of J are presented and discussed within the CLOPPA model.