A comparative multinuclear 1H, 13C, and 15N magnetic resonance study of organic thiocyanates and isothiocyanates

1 H, 13C, and 15N n.m.r. spectra of thiocyanato (RSCN) and isothiocyanato (RNCS) compounds, especially for the vinylic series R1C(SCN)=CHR2 and R1C(NCS)=CHR2, are reported. 15N Chemical shifts of thiocyanates (δca.–100 p.p.m.) and of isothiocyanates (δca.–275 p.p.m.) are very different, the value for the thiocyanate ion (SCN)– being intermediate (δ–165 p.p.m.). Comparison of the spectra of vinyl thiocyanates and isothiocyanates with those of the corresponding saturated compounds suggests that the SCN group exerts both attractive σ and π effects on the CC bond mainly through the intervention of the d orbitals of the S atoms. The NCS group appears to be slightly electron donating towards the double bond. Solvent effects on the 15N chemical shift of BunSCN and BunNCS are discussed in terms of Taft's linear solvation energy relationships.