Ketones conformations

For cyclic ketones conformational factors also come into play in determining enolate composition. 2-Substituted cyclohexanones are kinetically deprotonated at the C(6) methylene group, whereas the more-substituted C(2) enolate is slightly favored... 

The reduction of six-membered ring ketones (conformationally anchored) with sodium borohydride or lithium aluminum hydride to give predominantly the equatorial alcohol with... 

Rather phase-insensitive Norrish II photoproduct ratios are reported from irradiation of p-chloroacetophenones with a-cyclobutyl, a-cyclopentyl, a-cycloheptyl, a-cyclooctyl, and a-norbonyl groups [282], In each case, the E/C and cyclobutanol photoproduct ratios are nearly the same in neat crystals as measured in benzene or acetonitrile solutions. On this basis, we conclude that the reaction cavity plays a passive role in directing the shape changes of these hydroxy-1,4-biradicals. As long as the initial ketone conformation within the cavity permits -/-hydrogen abstraction (and these ketones may be able to explore many conformations even within their triplet excited state lifetime), the cavity free volume and flexibility allow intramolecular constraints to mandate product yields. 

Comparatively, the walls of a reaction cavity of an inclusion complex are less rigid but more variegated than those of a zeolite. Depending upon the constituent molecules of the host lattice, the guest molecules may experience an environment which is tolerant or intolerant of the motions that lead from an initial ketone conformation to its Norrish II photoproducts and which either can direct those motions via selective attractive (NB, hydrogen bonding) and/or repulsive (steric) interactions. The specificity of the reaction cavity is dependent upon the structure of the host molecule, the mode of guest inclusion, and the mode of crystallization of the host. 

Stereoselective reduction of cyclic ketones. Conformationally rigid ketones are reduced from the less hindered equatorial direction by the very bulky tris(t-butyldiethylmethoxy)aluminum hydride reagent. Thus 4-t-butylcyclohexanone furnishes a mixture of cis- and trans-alcohols in a 95 5 ratio. 

Methyl Ethyl Ketone, conforming to Specifications D740, having a refractive index 20 C (68 F) of 1.378 0.002 as determined in accordance with Test Method D 1218 or conforming to the following specifications ... 

Methyl Ethyl Ketone, conforming to Spedfication D740, or to Table 1. 

Suginome, H., Ohtsuka, T., Yamamoto, Y, Orito, K., Jaime, C., and Osawa, E., Photoinduced molecular transformations. 109. Conformational dependence of the stereochemistry of photochemical 1,3-acylshift of P,y-unsaturated cycHc ketones conformation specific photorearrangements of steroidal P,y-unsaturated cyclic ketones, 7a-homocholest-5-en-7a-one and 4a-homo-5a-cholest-l-en-4-one, /. Chem. Soc., Perkin Trans. 1,1247,1990. 

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