Ch_322b_16.05

Ch_322b_16.05 - Chapter 16.5 lecture note

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Addition Reactions of Aldehydes and Ketones Addition of Water and Alcohols: Hydrates and Acetals Hydrates of Aldehydes: Gem Diols When aldehydes and ketones are dissolved in aqueous media, an equilibrium is established between the carbonyl compound and its hydrate . The hydrate is a 1,1-diol or geminal diol . C=O R R' + H 2 O K C R' R O H OH hydrate This equilibrium depends on the size and electronic effects of the R groups. For most ketones, K' = K[H 2 O] = << 1 . (See table below.) Therefore, most ketones exists essentially 100% in the carbonyl form. Bulky R groups and electron-donating influences stabilize the carbonyl compound in the above equilibrium. Electron-withdrawing groups destabilize the carbonyl compound and promote formation of the hydrate. These factors are illustrated in the table that follows.
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Approximate Equilibrium Constants at 25 o C for the Reaction RR'C=O + H 2 O RR'C(OH) 2 carbonyl compound K' = K[H 2 O] = [RR'C(OH) 2 ] [RR'C=O] C=O H H 2 x 10 3 C=O H CH 3 1.3 C=O
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This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.

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Ch_322b_16.05 - Chapter 16.5 lecture note

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