¹⁵N nuclear magnetic resonance spectroscopy. Natural abundance ¹⁵N NMR of monosubstituted indoles

Abstract

Abstract 15 N chemical shifts of twenty‐four substituted indoles have been determined in natural abundance (in organic solvents) using Fourier transform NMR. The overall chemical shift range is 27 ppm, with groups in the 2‐, 3‐ and 5‐ring positions showing the largest substituent effects. Substituents capable of resonance interaction with the indole nitrogen give shifts in the expected directions but they cannot be correlated with known substituent parameters. Compounds measured in DMSO give 0·2 to 10·2 ppm downfield shifts with respect to the same compound measured in CDCl 3 . 13 C NMR data for previously unreported compounds are also reported.