1H and 13C 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

Gábor Szalontai, Péter Sándor, Felix Bangerter, L. Kollár

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Abstract

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. 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.

Original languageEnglish
Pages (from-to)216-222
Number of pages7
JournalMagnetic Resonance in Chemistry
Volume27
Issue number3
DOIs
Publication statusPublished - 1989

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Keywords

  • H and C dynamic NMR
  • Low‐temperature conformational analysis
  • Methylene proton non‐equivalence
  • Vinylogous diamide rotational barriers

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

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