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Conformational Analysis of Crown Ether Analogs in Solution: cis-Cyclohexyl-10-crown-3 as Studied via Low-Temperature 1H and 13C NMR Spectroscopy

✍ Scribed by G. W. Buchanan; M. Gerzain; K. Bourque

Publisher
John Wiley and Sons
Year
1997
Tongue
English
Weight
434 KB
Volume
35
Category
Article
ISSN
0749-1581

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✦ Synopsis

Two conformations of cis-cyclohexyl-10-crown-3 were detected in solution below 250 K using 1H NMR at 400 MHz and 13C NMR at 100 MHz. Chemical shift assignments were facilitated by spectra of two dideuterio derivatives. From relative peak area measurements, the conformation with the unit OÈCH 2 ÈCH 2 ÈCH 2 ÈO equatorial was found to be favored by 2.8 » 0.3 kJ mol-1 at 210 K. Results of a molecular mechanics calculation were compared with the experimental Ðndings. A remarkably large 13C chemical shift di †erence between conformers (ca. 10 ppm) was found for one of the methylene carbons bearing oxygen. Stereochemical factors contributing to the observed 13C shielding di †erences between conformers are discussed.

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Conformational analysis of crown ether a
Conformational analysis of crown ether analogs in solution: cis-cyclohexano-8-crown-3 as studied via low-temperature 13C and 1H NMR spectroscopy and molecular mechanics calculations
✍ G. W. Buchanan; A. B. Driega; R. C. Laister; K. Bourque 📂 Article 📅 1999 🏛 John Wiley and Sons 🌐 English ⚖ 100 KB 👁 2 views

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 š 0.4 kJ mol 1 . In the spectrum of the minor conformer at low temperature, a 9.6 ppm