Stereochemistry of crown ether analogs in the solid state and in solution. X-ray crystal structure, molecular mechanics calculations and nuclear magnetic resonance studies of benzo-16-crown-5
The X-ray crystal structure of the title molecule indicates that there is one 'unusual' transoid O-C-C-O torsional network in the macrocyclic ring. 13C NMR chemical shift differences between solution and solid state spectra are discussed in light of the solid state geometry. In the gas phase, calculations indicate that the X-ray crystal structure is not the most stable conformation. Rather, an optimized X-ray structure is favoured which retains the one trans O-C-C-O network, but has substantially expanded geometries for the remaining three O-C-C-O moieties. The total energy of this structure is 0.83 kcal/mol lower than that obtained for a structure whose geometry was obtained via preliminary MM + optimization, followed by further minimization via the AM1 method.
|Keywords||Macrocyclic polyethers, Solids, Solutions, Stereochemistry|
|Journal||Journal of Molecular Structure|
Buchanan, G.W, Laister, R.C., & Bensimon, C. (1998). Stereochemistry of crown ether analogs in the solid state and in solution. X-ray crystal structure, molecular mechanics calculations and nuclear magnetic resonance studies of benzo-16-crown-5. Journal of Molecular Structure, 471(1-3), 257–266. doi:10.1016/S0022-2860(98)00448-7