Dynamic 1 H NMR study around the carbon–carbon single bond and partial carbon–carbon double bond in the two particular phosphorus ylides and in an enaminoester

Herein, a series of separate dynamic 1 H NMR effects are reported at different temperatures within a particular enaminoester involving a phenanthridine. These effects are attributed to restricted rotation around the two single bonds such as carbon–carbon (H a C CH b ) and nitrogen–carbon (N CCOOCH 3 ). Activation energies ( E a ) for these interconversion processes in their rotational isomers are equal to 20 and 20 ± 1 kJ mol −1 , respectively. In addition, three dynamic 1 H NMR effects are investigated at different temperatures for a particular phosphorus ylide involving a 2‐indolinone around the carbon–carbon single bond (HC CPPh 3 ) within the two Z ‐ and E ‐rotational isomers and partial carbon–carbon double bond (OCH 3 ‐C C‐PPh 3 ). Activation energies ( E a ) for these interconversion processes in rotational isomers are equal to 53, 63 and 73 ± 1 kJ mol −1 , respectively. This behavior was also observed for other phosphorus ylide containing 2‐mercaptobenzoxazole around the carbon–carbon single bond and partial carbon–carbon double bond with their relevant activation energies containing 13, 10 and 75 ± 1 kJ mol −1 , respectively. Copyright © 2011 John Wiley & Sons, Ltd.