title: Effect of sulfur oxidation on the transmission mechanism of 4J(HH) NMR coupling constants in 1,3-dithiane.
abstract: Long-range 4J(HH) couplings in 1,3-dithiane derivatives are rationalized in terms of the effects of hyperconjugative interactions involving the S=O group. Theoretical and experimental studies of 4J(HH) couplings were carried out in 1,3-dithiane-1-oxide (2), cis-1,3-dithiane-1,3-dioxide (3), 1,3-dithiane-1,1,3-trioxide (4), and 1,3-dithiane-1,1,3,3-tetraoxide (5) compounds. Hyperconjugative interactions were studied with the natural bond orbital, NBO, method. Hyperconjugative interactions involving the LP(O), oxygen lone pair and sigma*(C2-S1) and sigma*(S1-C6) antibonding orbitals yield an increase of 4J(H(eq)-H(eq)) couplings. Long-range 4J(H(ax)-H(ax)) couplings were also observed between hydrogen atoms in axial orientation, which are rationalized as originating in hyperconjugative interactions involving the bonding sigma(C6-H(ax)) and antibonding sigma*(S=O) orbitals. The symmetry for orbital interactions is possible only when the S=O group is in the axial orientation.
authors.affiliation: Departamento de Química, Universidade Estadual de Maringá, CEP-87020-900, Maringá, PR, Brazil.
authors.forename: Gisele F
authors.initials: GF
authors.lastname: Gauze
authors.forename: Ernani A
authors.initials: EA
authors.lastname: Basso
authors.forename: Rubén H
authors.initials: RH
authors.lastname: Contreras
authors.forename: Cláudio F
authors.initials: CF
authors.lastname: Tormena