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NMR chemical shift substituent effects: 2‐α‐monosubstituted N , N ‐diethylacetamides
Author(s) -
Martins Marcos A. P.,
Rittner Roberto
Publication year - 1980
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270140619
Subject(s) - chemical shift , substituent , methylene , steric effects , chemistry , electronegativity , conformational isomerism , proton , proton nmr , resonance (particle physics) , crystallography , computational chemistry , stereochemistry , medicinal chemistry , molecule , organic chemistry , physics , particle physics , quantum mechanics
1 H NMR chemical shifts for some α‐hetero‐substituted N , N ‐diethylacetamides were recorded. The resonance assignments for the syn ‐ and anti ‐methylene and ‐methyl protons have been made unambiguously through their aromatic solvent induced shifts and are opposed to the literture assignments for the N ‐methylene protons. An empirical relationship between the Charton polar (σ L ) and steric (V) parameters and the α‐methylene proton resonances was found. The N ‐methylene proton chemical shifts also showed a qualitative dependence on the α‐substituent electronegativity, while the N ‐ethyl methyl proton chemical shifts were related to the α‐substituent steric effects. The Paulsen and Todt anisotropic model and the more populated rotamers proposed seem to explain the results very well.