¹H chemical shifts in NMR. Part 27: proton chemical shifts in sulfoxides and sulfones and the magnetic anisotropy, electric field and steric effects of the SO bond

Abstract

The (1)H chemical shifts of a series of sulfoxide and sulfone compounds in CDCl(3) solvent were obtained from experiment and the literature. These included dialkyl sulfoxides and sulfones (R(2)SO/R(2)SO(2), R = Me, Et, Pr, n-Bu), the cyclic compounds tetramethylene sulfoxide/sulfone, pentamethylene sulfoxide/sulfone and the aromatic compounds p-tolylmethylsulfoxide, dibenzothiopheneoxide/dioxide, E-9-phenanthrylmethylsulfoxide and (E) (Z)-1-methylsulfinyl-2-methylnaphthalene. The spectra of the pentamethylene SO and SO(2) compounds were obtained at -70 degrees C to obtain the spectra from the separate conformers (SO) and from the noninverting ring (SO(2)). This allowed the determination of the substituent chemical shifts (SCS) of the SO and SO(2) functional groups, which were analyzed in terms of the SO bond electric field, magnetic anisotropy and steric effect for long-range protons together with a model (CHARGE8d) for the calculation of the two and three bond effects. After parameterization, the overall root mean square (RMS) error (observed-calculated) for a dataset of 354 (1)H chemical shifts was 0.11 ppm. The anisotropy of the SO bond was found to be very small, supporting the dominant single bond S(+)--O(-) character of this bond.

Observed and calculated 1H and 13C chemical shifts induced by the in situ oxidation of model sulfides to sulfoxides and sulfones

“…The NMR spectra indicate a fast equilibrium of the two energetically equivalent chair forms of 8A and 8C in solution (discussion concerning conformation of thiacyclohexanes was recently reviewed43). It was found previously that sulfoxide 8B appears in solution as a mixture of two conformers with an oxygen atom in the axial or equatorial position42 (Fig. 6).…”

“…To acquire deeper insight into the sulfoxide group anisotropy42 pattern, we performed a series of calculations of the individual hydrogen chemical shifts in dimethylsulfoxide ( 1B ), where the torsion angle CSCH was adjusted to cover the entire range of the free rotation of the methyl group (360°) with a step of 10° (Fig. 3).…”

Stereoisomeric 2-butylphenylsulfoxides and their binding modes in the adduct formation with an enantiopure dirhodium tetracarboxylate complex

“…The reason for this systematic chemical shift divergence is, of course, the stereochemistry of the sulfoxides. Some 13 C and 1 H chemical shift trends exerted by S (+) -O (À) groups on neighbouring hydrogen and carbon atoms have been reported [16,18] but they were derived from compounds containing rigid six-membered rings in chair-conformation whereas the sulfoxides 1 and 2 are mixtures of more than one open-chain conformers (see below). Therefore, empirical correlations between those molecular systems with respect to effects on chemical shifts failed or appeared to be speculative.…”

“…Sulfoxides offer both types of ligand categories simultaneously, a soft sulfur atom with a free electron pair and a hard oxygen atom; the S (+) -O (À) bond is predominantly a single bond [16]. The question is which of these two atoms, O or S, is the binding site.…”

Complete assignment of 1H and 13C NMR spectra of α‐phenylsulfinyl‐N‐methoxy‐ N‐methylpropionamide and some p‐substituted derivatives

“…Empirically calculated chemical shifts are in close agreement to the experimental values. [13,14] The 13 C NMR chemical shifts for 1-5 are presented in Table 3 and the signals of the diastereomers diast 1 and diast 2 were assigned through HETCOR experiments of 5, taken as the prototype for the whole series. The signals at δ ∼ 29.8 − 32.4 and at δ ∼ 61.3 − 61.9 ppm for 1-5 correspond to C-1 and C-2, respectively.…”