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Isomeric cis ‐cyclohexano‐13‐crown‐4 ethers: a low‐temperature 1 H and 13 C NMR investigation
Author(s) -
Buchanan G. W.,
Gerzain M.,
Laister R. C.
Publication year - 1998
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(199810)36:10<687::aid-omr352>3.0.co;2-s
Subject(s) - chemistry , ring flip , conformational isomerism , cyclohexane , carbon 13 nmr , computational chemistry , chemical shift , nuclear magnetic resonance spectroscopy , stereochemistry , ring (chemistry) , molecule , organic chemistry
The two positionally isomeric cyclohexanotetraoxacyclotridecanes (13‐crown‐4 ethers) were synthesized and studied via low‐temperature NMR methods. For the 1,4,8,11‐tetraoxa isomer, the cyclohexane ring inversion is a degenerate process, whereas for the 1,4,7,11‐tetraoxa isomer, a preference of 1.4 kJ mol ‐1 for the form in which the propyleneoxy group is equatorial was determined. Molecular mechanics calculations using MM + indicated a preference of 0.6 kJ mol ‐1 for this conformer. Resonance assignment was facilitated by the synthesis of a selectively deuterated derivative and by COSY, HMQC and HMBC experiments. The results were compared with those for the related 10‐crown‐3 system and 13 C chemical shift trends are discussed in terms of MM + calculated geometries. © John Wiley & Sons Ltd.