1H and13C dynamic NMR study of theE,Z isomers of vinylogous diamides. Effect of conjugation and electrostatic and steric repulsion on the C(O)N rotation barriers and low-temperature conformation
作者:Gábor Szalontai、Péter Sándor、Felix Bangerter、László Kollár
DOI:10.1002/mrc.1260270304
日期:1989.3
A 1H dynamic NMR study was carried out on N,N‐diethylmethacrylamide (1a), N,N,N′,N′‐tetraethylitaconamide (2), N,N,N′,N′‐tetraethylcitraconamide (3) and N,N,N′,N′‐tetraethylmesaconamide (4) over a wide temperature interval. Amide rotational barriers were determined from the coalescence temperatures. In 3 a second dynamic process was observed below 240 K, which made the geminal methylene protons non‐equivalent
对 N,N-二乙基甲基丙烯酰胺 (1a)、N,N,N',N'-四乙基衣康酰胺 (2)、N,N,N',N'-四乙基柠康酰胺 (3) 和 N 进行了 1H 动态核磁共振研究, N,N',N'-四乙基美沙康酰胺 (4) 在很宽的温度区间内。酰胺旋转屏障由聚结温度确定。在 3 中,在 240 K 以下观察到第二个动态过程,这使得孪生亚甲基质子不等价。该现象被解释为由酰胺羰基的静电和/或空间排斥引起的非平面构象。同核 NOE 实验揭示了所研究化合物的 s-cis, s-cis' 构象。