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

Abstract

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.