¹³C NMR of organosulphur compounds: I—the effects of sulphur substituents on the ¹³C chemical shifts of alkyl chains and of S‐heterocycles

Abstract

Abstract-The13C NMR spectra have been determined of: (i) aliphatic compounds having at one end a functionalized sulphur atom (-SH, -S-, -SMe, -S(O)Me, -SO,Me and -S-'Me,) and (ii) saturated sulphur heterocycles variously substituted at the S-atom (\S, \SO '\SO, and 'xS Me). The results are discussed in terms of the familiar deshielding effects for CL-and B-carbons and shielding effects for y-carbons, exerted by the sulphur atom itself and/or by the atoms or groups of which the sulphur function is made up. The 11-effect of the S-atom appears to be nearly independent of the nature of the S-function and of comparable magnitude to that of an aliphatic carbon (-2.5 t--3.0 ppm). Surprisingly, however, a S-CH, group shields the carbon in y position with respect to CH, by an amount (-5.4 ppni) which is more than twice that (-2.5 ppm) exerted by the aliphatic y-carbon on the S-CH, carbon itself. As to the cyclic compounds, the shieldings of the G(-and 8-carbons can be rationalized in terms of the conformational orientation of the substituent at sulphur, and the equilibrium distribution of the conformers. The results confirm the great value of 13C NMR for configurational and conformational assignment of S-heterocycles. / / ' / /'WITH the exception of a recent paper by Buchanan and collaborators, dealing with aryl methyl sulphides, sulphoxides and sulphones,l only scattered information is available in the literature on the 13C chemical shifts of sulphur-containing organic compounds. The present report contributes some systematic observations on the effect of such sulphur functions as: thiol, -SH, the sulphone, >SO, and the sulphonium cation, >S 1-R, on the 13C chemical shifts of typical aliphatic and S-heterocyclic structures.The main purpose of this work was to derive empirical criteria (additivity rules) to be used as groundwork for the conformational analysis of saturated sulphur heterocycles. The more numerous and systematic observations concern sulphoxides and sulphonium cations. We particularly concentrated on these functions since they are known to be pyramidal and configurationally stable. Therefore, when an integral part of a ring, they were expected to produce characteristic 13C chemical shift effects that, while permitting facile configurational assignment, would also greatly aid the thiolate anion, -S-, sulphide, -S-, sulphoxide, ,S-0, \

Reduction of Sulfoxides to Sulfides in the Presence of Copper Catalysts

“…The solvent was removed and the residue was purified by column chromatography. The analytical properties of the corresponding sulfides are in agreement with literature[63][64][65][66][67][68][69][70][71].Diphenylsulfide (1a): R f = 0.75 (n-hexane:ethyl acetate 1:5); 1 H NMR (CDCl 3 , 200 MHz): d = 7.26-7.47 ppm (m, 10H); 13 C NMR (CDCl 3 , 50 MHz): d = 135.8, 131.0, 129.2, 127.0 ppm; MS (ESI) m/z = 186 (100, M ? ), 152 (11), 92 (19), 77 (27), 65 (20), 51 (43).…”

Effects of methyl substitution in 4-silathiane S-oxides on the stereochemistry and1JCHcoupling constants: Buttressing effect of axial sulfinyl group as the origin of the reverse Perlin effect

“…The 1 H NMR spectrum of 3eee also shows the corresponding protons to be identical in † Here we follow the terminology used in [19] where it was referred to as β-and γ -effect as reflecting the effect on atoms β and γ to oxygen. This is distinct from α-and β-effect used by the same authors [20] to describe the effect of the whole substituent on the carbons α and β to a sulfur-containing moiety. The orientation of the S=O group in 3eee and 3aae was determined by analysis of the 13 C chemical shifts for atoms C-3 and C-5 (table 1) and vicinal coupling constants 3 J (H-2,H-3) and 3 J (H-5,H-6).…”

“…† The nature of the β-and γ -effects was disputable. In [20] it was ascribed to the electrostatic effect of dipolar S=O bond, but it was called into question in [21] since the same effect is observed for nonpolar C-C bonds, like in methylcyclohexanes. However, regardless of its nature, the effect itself is a reliable criterion of arrangement of the S=O group.…”

A novel synthesis of 2,4,6-trithiaheptane and its conversion into 2,6-bis(methylthio)thiane. Spectral properties of some thiaalkanes

“…The parameters reported in Tables 3 and 4 usefully supplement data available (18)(19)(20)(21)(22)(23) for openchain organosulfur compounds. For example, it is known (18) that the a, p, y, and 6 substituent effects of a sulfenyl sulfur atom in simple sulfides are little different from those of a carbon atom.…”

“…The 13C chemical shifts of the trithiaheptanes reported in Table 3 confirm this. For C(1), the terminal methyl group of heptane, 6 (13C) = 13.9 which changes to 6 13.7 for the corresponding carbon of di-n-propyl sulfide (18) and to 6 14.2 in l a , where heptane carbons C(2), C(4), and C(6) aie all replaced by sulfur atoms. The change in chemical shift for C (3) in the same series is from 6 32.4 to 6 34.6 to 6 35.…”