Dolbier HW Solutions 350

Dolbier HW Solutions 350 - 444 ALDEHYDES AND KETONES:...

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( d ) The hydroxyl group may be on the same side as the double bond or on the opposite side. The anti alcohol is observed to be formed in greater amounts (85:15) on reduction of the ke- tone with LiAlH 4 . Steric factors governing attack of the hydride reagent again explain the major product observed. 17.24 ( a ) Aldehydes undergo nucleophilic addition faster than ketones. Steric crowding in the rate- determining step of the ketone reaction raises the energy of the transition state, giving rise to a slower rate of reaction. Thus benzaldehyde is reduced by sodium borohydride more rapidly than is acetophenone. The measured relative rates are ( b ) The presence of an electronegative substituent on the a -carbon atom causes a dramatic in- crease in K hydr . Trichloroethanal (chloral) is almost completely converted to its geminal diol (chloral hydrate) in aqueous solution. Electron-withdrawing groups such as Cl 3 C destabilize carbonyl groups to which they are at-
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