Carbon-13 NMR spectra of a series of para-substituted phenyl isothiocyanates. Linear free energy relationships for carbon-13 substituent chemical shifts

✍ Scribed by Ronald G. Jones; Grace Allen

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 756 KB
• Volume: 19
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270190408

✦ Synopsis

Carbon-13 chemical shifts are reported for 16 para-substituted phenyl isothiocyanates measured at 1 and 1Omol 9'0 in chloroform-d solution. Data for the -N=C==S group were not obtained at lmol 9'0, but concentration effects for the other resonances were negligible. Hammett, dual substituent parameter (DSP) and DSP-nonlinear resonance (DSP-NLR) analyses were used to evaluate substituent effects on the substituent chemical shifts (SCS) for the ipso-carbon (C-1), C-2, and the -N=C==S carbon atoms. A good Hammett correlation was observed for C-1 (p; = 8.1 ppm, r = 0.98 at 1 mol %) but was improved for the higher order correlations with the following results, DSP: p, = 5.4, ha = 22.2, r = 0.998; DSP-NLR p, = 5.6, pRa = 20.5, E = -0.22, r = 0.999. The 10 mol 9'0 data were very shnilar except the value of E was -0.26 and confirms the phenyl-bonded -N=C=S moiety as a mild electron acceptor substituent. Hammett correlations were unsuccessful for the C-2 data, but fairly good results were obtained from the higher order analyses. For the lmol YO data, D S P pr=1.6, p~'=-2.0, r=0.