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1 H and 13 C dynamic NMR study of the E , Z isomers of vinylogous diamides. Effect of conjugation and electrostatic and steric repulsion on the C(O)N rotation barriers and low‐temperature conformation
Author(s) -
Szalontai Gábor,
Sándor Péter,
Bangerter Felix,
Kollár László
Publication year - 1989
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260270304
Subject(s) - chemistry , geminal , steric effects , amide , homonuclear molecule , methylene , stereochemistry , nuclear magnetic resonance spectroscopy , crystallography , medicinal chemistry , molecule , organic chemistry
A 1 H 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. The phenomenon is interpreted in terms of a non‐planar conformation caused by electrostatic and/or steric repulsion of the amide carbonyls. Homonuclear NOE experiments revealed an s ‐cis, s ‐ cis ′ conformation for the compounds studied.