3. To find the lowest energy structure for the isomers of
either 1-hydroxy-cis decalin 4
or the lowest energy isomers of both 1-hydroxy-trans-decalin 5 and 2-hydroxy-trans-decalin 6.
Students working in pairs must complete both options
The first task is to decide how many stereoisomers of the compound exist, and for each of these how many stable conformers.
The more complex case is the cis-decalol 4. Take the structure fragment of cis-decalin and replace each of the hydrogens adjacent to one ring junction (there are four) with a hydroxyl group. Satisfy yourself how many stereoisomers there are, and how many distinct conformers of each stereoisomer and carry out energy minimisations as necessary. Record the structures by making 3-D drawings and note their strain energies. What conclusions can you draw about the energy difference of the axial and equatorial isomers ?
Alternatively, carry out a similar procedure for both compounds 5 and 6, and record your conclusions on the strain energy difference between axial and equatorial isomers here.
In simple cyclohexanols, the axial conformer is around 2.5 KJmol-1 (0.6 Kcals mole-1) less stable than the equatorial conformer. Do your results with decalols fit with this?
As part of your write-up read about the stereochemical course of the reduction of conformationally restricted cyclohexanols with hydridic reducing agents. You can find review of this topic:
D. C. Wigfield, Tetrahedron , 1979, 35, 449.
An University of Oxford Chemistry IT Centre Course © Copyright 1997 John Brown & Karl Harrison