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1 H NMR studies of proton transfer and σ‐complex formation in the reactions of N ‐substituted picramides with oxygen and nitrogen bases
Author(s) -
Crampton Michael R.,
Gibson Brenda,
Matthews Raymond S.
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.1270130613
Subject(s) - chemistry , methoxide , sodium methoxide , adduct , benzylamine , methanol , amide , proton nmr , piperidine , methylene , medicinal chemistry , photochemistry , base (topology) , ring (chemistry) , proton , stereochemistry , organic chemistry , mathematical analysis , physics , mathematics , quantum mechanics
1 H NMR measurements of N ‐substituted picramides in dimethyl sulphoxide‐methanol containing sodium methoxide show that the two major modes of 1:1 interaction involve transfer of an amino proton to give the conjugate base or methoxide attack at the 3‐position to give a σ‐adduct. The proportion of parent reacting by the latter pathway increases as the proportion of methanol in the solvent increases. Some comparative measurements in isopropanol‐dimethyl sulphoxide show that relative to methoxide the isopropoxide ion has a greater propensity for proton abstraction than for base addition. Reaction of the substrates with amide ions derived from piperidine or from benzylamine gives σ‐complexes by attack at unsubstituted ring positions. In the benzylamide adducts spin coupling is observed between the amino proton and the adjacent ring and methylene protons.