Hydrogenation equatorial alcohols from

Catalytic hydrogenation in neutral medium gives an axial alcohol from sterically hindered ketone and an equatorial alcohol from sterically unhindered ketones. 

These mechanistic interpretations can also be applied to the hydrogenation of cyclohexanones. In acid, the carbonium ion (19) is formed and adsorbed on the catalyst from the least hindered side. Hydride ion transfer from the catalyst gives the axial alcohol (20). " In base, the enolate anion (21) is also adsorbed from the least hindered side. Hydride ion transfer from the catalyst followed by protonation from the solution gives the equatorial alcohol (22). 

Hydrogenations of cyclohexanones in basic media leads to the formation of the more stable, equatorial alcohol, 18, as the primary product (Eqns. 18.18-19). With basic Raney nickel catalysts, the predominance of equatorial alcohol has been shown to arise from the isomerization of the initially produced axial alcohol under hydrogenation conditions. The use of platinum oxide with its alkaline impurity also leads to extensive equatorial alcohol formation unless acetic acid is used as the solvent. This basic impurity was shown to be... 

When we compare the rates of reaction of axial and equatorial hydroxyl groups in six-membered rings, we find that the reactions of the axial alcohols are faster than those of equatorial alcohols. This tells us that it is the second step, the elimination process, that is rate determining the hydrogen to be removed from the axial alcohol is in the equatorial position and hence more accessible (Figure 10.41). 

Carbohydrates have been included in the wide range of molecules used in the parameterization of MM2 and of MM3. Alcohol and ether parameters have usually been determined from simple alcohols and ethers themselves. However, carbohydrates contain some unusual features in the acetal linkages, and in the many vicinal hydrogen-bonded hydroxyl groups. The "anomeric effect", first discovered by Edward (15) and popularized by Lemieux (16.), is best known in carbohydrates, although, of course, it occurs in other classes of compounds as well. One apparent result of this effect is that an axial alkoxy substituent is often more stable than the corresponding equatorial substituent when attached at the Cl position of a tetrahydropyranyl ring. This effect can be... 

Biochemical reduction of a,/3-unsaturated ketones using microorganisms (best Beauveria sulfurescens) takes place only if there is at least one hydrogen in the /3-position and the substituents on a-carbons are not too bulky. The main product is the saturated ketone, while only a small amount of the saturated alcohol is formed, especially in slightly acidic medium (pH 5-5.5). The carbonyl is attacked from the equatorial side. Results of biochemical reduction of 5-methylcyclohex-2-en-l-one are illustrative of the biochemical reduction by incubation with Beauveria sulfurescens after 24 hours 74% of the enone was reduced to 3-methylcyclohexanone and 26% to 3-methylcy-clohexanol containing 55% of cis and 45% of trans isomer. After 48 hours the respective numbers were 70% and 30%, and 78% and 22%, respectively [878]. 

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