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( 15 N) acetamide in polar solvents: Hindered internal rotation and intermolecular interactions
Author(s) -
Umemoto Kimiko,
Ouchi Kenichi
Publication year - 1981
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.1270150104
Subject(s) - acetamide , chemistry , amide , acetonitrile , pyridine , intermolecular force , solvent , chemical shift , hydrogen bond , activation energy , solvent effects , crystallography , molecule , organic chemistry
The 1 H spectrum of ( 15 N)acetamide has been measured in dimethyl sulphoxide (DMSO), methyl propyl ketone (MPK), 1,3‐dioxane, 1,4‐dioxane, D 2 O, acetonitrile and pyridine‐ d 5 at various temperature intervals within the range of 278–343 K. From the temperature dependence of the NMR spectra of the amide protons, the free energy of activation, ΔG ≠ , for hindered rotation about the central CN bond was determined by means of total line shape analysis in the four solvents DMSO, MPK and the two dioxanes. Observed values of ΔG ≠ (298 K) (72.7 in DMSO, 70.1 in MPK, 70.0 in 1,3‐dioxane and 70.1 kJ mol 1 in 1,4‐dioxane) were not very sensitive to the choice of solvent or concentration. The concentration dependence of the internal chemical shift between the amide protons was studied in MPK, D 2 O, acetonitrile and pyridine‐ d 5 . The free energy of activation and the internal chemical shift are discussed on the basis of solvent‐amide and amide–amide specific hydrogen bonding interactions, and in comparison to the results of molecular orbital calculations.