From Cyclohexane to 2-Hydroxy-3-oxanone:  A Conformation Study

Density functional calculations are reported on all stable chair and twist-boat conformations of cyclohexane, cyclohexanol, oxane, cyclohexanone, 3-oxanone, 2-oxanol, 2-hydroxycyclohexanone, and 2-hydroxy-3-oxanone. With just one exception, the chair conformation is predicted to lie lower in energy than the twist-boat conformations. Either individually replacing a hydroxyl for hydrogen, introducing an oxygen into the ring, or incorporating a carbonyl group into cyclohexane reduces the energy difference between chair and twist-boat. In cyclohexanol the equatorial chair lies lower in energy than the axial chair. The axial chair anomers of 2-oxanol, 2-hydroxycyclohexanone, and 2-hydroxy-3-oxanone lie lower in energy than the equatorial chair anomers. In 2-hydroxy-3-oxanone the equatorial chair lies higher in energy than one of the twist-boat conformations. Stereoselective reduction of 2-hydroxy-3-oxanones is shown to result from sterically controlled attack.