Effect of sulfur oxidation on the transmission mechanism of 4J(HH) NMR coupling constants in 1,3-dithiane.
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.
Gauze
Gisele F
GF
Departamento de Química, Universidade Estadual de Maringá, CEP-87020-900, Maringá, PR, Brazil.
Basso
Ernani A
EA
Contreras
Rubén H
RH
Tormena
Cláudio F
CF