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Conformational preferences of 2‐methoxypyridine from 1 H and 13 C NMR and from STO‐3G molecular orbital calculations
Author(s) -
Blonski Wayne J. P.,
Hruska Frank E.,
Wildman Timothy A.
Publication year - 1984
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.1270220807
Subject(s) - conformational isomerism , crystallography , methyl group , chemistry , group (periodic table) , ring (chemistry) , molecular orbital , relaxation (psychology) , hydrogen bond , proton , molecule , physics , psychology , social psychology , organic chemistry , quantum mechanics
Observable coupling over five formal bonds between the methoxy group protons and the ortho ring proton in 2‐methoxypyridine, coupliugs between the methoxy group carbon and ring protons, and methoxy carbon spin‐lattice relaxation times are all consistent with a preference for the planar cis conformer, in which conjugation is favoured and repulsions between the methyl group and the ortho hydrogen are reduced. Small‐amplitude torsioas about the C‐2–O bond may carry the methoxy group away from this orientation, but more distant conformations can probably be excluded. Methyl group rotation is less hindered in the cis than in the trans conformer. Molecular orbital calculations at the STO‐3G level, with complete geometry optimization, support the conduskus drawn from experimental evidence.