NMR Study of Substituent Effects in 4-Substituted and 4,4'-Disubstituted Diphenyl Sulphides

Article abstract of DOI:10.1002/mrc.1260251117

The proton and carbon NMR spectra of nine 4-X-diphenyl sulphides (series 1), seven 4-X-4'-NO2-diphenyl sulphides (series 2) and eight 4,4'-X₂-diphenyl sulphides (series 3) have been obtained.Correlation of the 13C chemical shifts with the appropriate substituent chemical shifts (SCS) for monosubstituted benzenes (Lynch plots) show an enhancement of substituent effect at C-1 (carbon para to the substituent) in series 1 ans 2, but not in series 3.The carbons of the unsubstituted ring in series 1 also correlate with C_p-SCS, with slopes of less than unity; correlation for C-1' has a negative slope.Dual substituent parameter (DSP) correlations of the 13C chemical shifts with ?_I/?^o_R are good to exellent for all the carbons of series 1 compounds, except those ortho to the substituent X.The carbons meta to the substituent X correlate well, but with negative values for ρ_I and ρ_R, although showing a scattered Lynch plot.Similar correlations are found with some carbon shifts in series 2, and with C-1 shifts in series 3.It is concluded that (a) reverse resonance effects are operative at the position meta to the variable substituent by virtue of the sulphur substituent ortho to that carbon; (b) there is transmission of inductive (field) and resonance effects from one aryl ring to the other, except when both rings carry substituents of the same electronic character (series 3); (c) there is some evidence for ?-polarization in the unsubstituted phenyl ring of series 1 compounds.Key words 1H NMR 13C NMR Diphenyl sulphides substituent effects