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Conformational analysis of crown ether analogs in solution: cis ‐cyclohexano‐8‐crown‐3 as studied via low‐temperature 13 C and 1 H NMR spectroscopy and molecular mechanics calculations
Author(s) -
Buchanan G. W.,
Driega A. B.,
Laister R. C.,
Bourque K.
Publication year - 1999
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/(sici)1097-458x(199906)37:6<401::aid-mrc469>3.0.co;2-z
Subject(s) - conformational isomerism , chemistry , molecular mechanics , nuclear magnetic resonance spectroscopy , crystallography , molecule , crown ether , chemical shift , stereochemistry , spectroscopy , ether , cyclohexane conformation , computational chemistry , molecular dynamics , hydrogen bond , organic chemistry , ion , physics , quantum mechanics
Two conformations of the cis ‐cyclohexano‐8‐crown‐3 molecule were detected at 185 K. From relative 13 C NMR peak area measurements, the conformation with the O— CH 2 — O unit equatorial was found to be favoured by 4.4 ± 0.4 kJ mol −1 . In the spectrum of the minor conformer at low temperature, a 9.6 ppm 13 C chemical shift difference is present between the two methine carbons. Transannular 1,4 H–H interactions are deemed to be partly responsible for this effect. Merck Molecular Force Field (MMFF) calculations indicate a preference of ca 1.8 kJ mol −1 for the most populated conformation. A boat–chair conformation is present in the 1,3,6‐trioxocane ring of the major conformer whereas a twist boat–chair is preferred in the minor form. Two other conformations with populations of ≥ 1% were identified. Copyright © 1999 John Wiley & Sons, Ltd.