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
Two conformations of the cis-cyclohexano-8-crown-3 molecule were detected at 185 K. From relative 13C NMR peak area measurements, the conformation with the O - CH2 - 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 9.6ppm 13C 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
|Keywords||1,3,6-Trioxacyclooctane, 13C NMR, 1H NMR, Crown ether analogs, NMR, Stereochemistry, Trioxocane|
|Journal||Magnetic Resonance in Chemistry|
Buchanan, G.W, Driega, A.B., Laister, R.C., & Bourque, K. (1999). 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. Magnetic Resonance in Chemistry, 37(6), 401–406.