PSEUDOHALOGEN CHEMISTRY .12. NMR AND IR STUDIES OF SUBSTITUENT EFFECTS IN 4-SUBSTITUTED THIOCYANATOBENZENES

H-1 and C-13 NMR chemicals shifts for 15 4-X-thiocyanatobenzenes have been measured at high dilution in CDCl3 solution. Substituent chemical shifts for the SCN group were derived from the data for thiocyanatobe nzene. Excellent substituent-shift correlations (r > 0.995) were obtai ned for the SCN carbon using single and dual substituent parameter (SS P and DSP) approaches, and for the ring carbons using SSP, modified DS P, and triple substituent parameter (TSP) approaches. The SCN carbon e xperiences a reverse substituent effect through both polar and resonan ce components of the electronic effect of X. Reverse resonance effects were also observed for C-2(6) and C-4, and reverse polar effects for C-2(6) and C-3(5). The SCN group causes a 50% enhancement of the norma l para SCS values of X at C-1. SSP and DSP substituent-shift correlati ons were successful for H-3(5) but only fair or poor for H-2(6). IR SC N stretching frequencies were also measured and correlated successfull y with substituent parameters using SSP and DSP methods; in contrast t o delta SCN, vSCN shows a normal substituent effect.