Dynamic 1H NMR study of 4-methylphenoxyimidoyl azides: conformational or configurational isomerisation?

Dynamic 1H NMR (500 MHz) investigation of 4-methylphenoxyimidoyl azides (4-CH3–C6H4–O–CN–Y)–N3, Y=4-CH3–C6H4–SO2–, 4-Br–C6H4–SO2–, C6H5SO2–, CH3–SO2–, –CN in acetone-d6 at temperature range of 195–280 K is reported. The observed free energy barrier (almost 12 kcal mol−1) is attributed to conformational isomerisation about the N–S bond for Y=4-CH3–C6H4–SO2–, 4-Br–C6H4–SO2–, C6H5SO2–, CH3–SO2– and (almost 14 kcal mol−1) to configurational isomerisation (E/Z) about CN bond for Y=–CN.