✦ LIBER ✦

Isomeric cis-cyclohexano-13-crown-4 ethers: a low-temperature 1H and 13C NMR investigation

✍ Scribed by G. W. Buchanan; M. Gerzain; R. C. Laister

Publisher: John Wiley and Sons
Year: 1998
Tongue: English
Weight: 443 KB
Volume: 36
Category: Article
ISSN: 0749-1581
DOI: 10.1002/(sici)1097-458x(199810)36:10<687::aid-omr352>3.0.co;2-s

No coin nor oath required. For personal study only.

✦ Synopsis

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 MMindicated 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 13C chemical shift trends are discussed in terms of MMcalculated geometries.

📜 SIMILAR VOLUMES

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

Conformational Analysis of Crown Ether A

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

✍ G. W. Buchanan; M. Gerzain; K. Bourque 📂 Article 📅 1997 🏛 John Wiley and Sons 🌐 English ⚖ 434 KB 👁 2 views

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

Thermodynamic origin of cis/trans isomer

Thermodynamic origin of cis/trans isomers of a proline-containing β-turn model dipeptide in aqueous solution: A combined variable temperature 1H-NMR, two-dimensional 1H,1H gradient enhanced nuclear overhauser effect spectroscopy (NOESY), one-dimensional steady-state intermolecular 13C,1H NOE, and molecular dynamics study

✍ Anastasios Troganis; Ioannis P. Gerothanassis; Zafiria Athanassiou; Thomas Mavro 📂 Article 📅 2000 🏛 Wiley (John Wiley & Sons) 🌐 English ⚖ 178 KB 👁 1 views

The cis/trans conformational equilibrium of the two Ac-Pro isomers of the beta-turn model dipeptide [13C]-Ac-L-Pro-D-Ala-NHMe, 98% 13C enriched at the acetyl carbonyl atom, was investigated by the use of variable temperature gradient enhanced 1H-nmr, two-dimensional (2D) 1H,1H nuclear Overhauser eff