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Effect of carbonyl substituents on the barrier to rotation in N ‐ethyl‐ N ‐methylamides
Author(s) -
Bonacorso Helio G.,
Caro Miguel S. B.,
Zanatta Nilo,
Martins Marcos A. P.
Publication year - 1993
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.1260310507
Subject(s) - chemistry , steric effects , medicinal chemistry , alkyl , electronic effect , gibbs free energy , steric factor , internal rotation , nuclear magnetic resonance spectroscopy , computational chemistry , stereochemistry , organic chemistry , thermodynamics , physics , mechanical engineering , engineering
The barriers to rotation about the C(O)N bond for 13 α‐alkyl‐ and α‐halo‐substituted N ‐theyl‐ N ‐methylamides were determined by 1 H NMR spectroscopy at coalescence temperature. Plots of Gibbs free energy (Δ G °) and Gibbs energy of activation (Δ G ‡) values against Charton's electronic and steric parameters of the α‐carbonyl groups allows the conclusion that both the isomeric preference and the barrier to rotation about the C(O)N bond of the N ‐ethyl‐ N ‐methylamides depend mainly on the steric effect of the α‐carbonyl group.