Theoretical Analysis of interactions affecting 1J(C,H) NMR couplings in an sp3 hybridized carbon atom. Par I: The exoanomeric effect in 3-metoxy-1,2,4,5-tetroxane.

NELIDA MARIA PERUCHENA; CONTRERAS, R. H.

JOURNAL OF MOLECULAR STRUCTURE THEOCHEM

ELSEVIER SCIENCE BV

Lugar: Elsevier; Año: 1995 vol. 338 p. 25 - 30

0166-1280

It is studied how much and under which conditions the anomeric effect affects a 1J(CH) coupling constant. 3-Methoxy-1,2,4,5-tetroxane and related compounds are chosen as model systems. With the polarization propagator formalism the 1J(C3H) coupling is decomposed into contributions originated in different occupied and vacant localized molecular orbitals representing, respectively, bonds or lone pairs, and antibonding orbitals. It is found that, for a highly polar C-H bond, the anomeric effect increases the s character of its antibonding orbital, giving a large 1J(CH) coupling. Under these circumstances, the value of this coupling departs notably from the commonly accepted proportionality between onebond J(CH) couplings and the s character of its C-H bond.