Claisen reaction- Ester leaving group

Claisen reaction- Ester leaving group - Carbonyl...

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1 Carbonyl Condensation Reactions The Aldol Reaction In the aldol reaction , two molecules of an aldehyde or ketone react with each other in the presence of a base to form a β -hydroxy carbonyl compound .
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2 The Aldol Reaction The mechanism of the aldol reaction occurs in three steps. Carbonyl Condensation Reactions
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3 The Aldol Reaction The aldol reaction is a reversible equilibrium, so the position of the equilibrium depends on the base and the carbonyl compound. ¯ OH Is the base typically used in an aldol reaction. Although with ¯ OH only a small amount of enolate is formed, this is appropriate because the starting aldehyde is needed to react with the enolate in the second step of the reaction. Aldol reactions can be carried out with either aldehydes or ketones. With aldehydes, the equilibrium usually favors products, but with ketones the equilibrium favors the starting materials. However, there are ways of driving the equilibrium to the right. Carbonyl Condensation Reactions
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4 The Aldol Reaction Recall that the characteristic reaction of aldehydes and ketones is nucleophilic addition. An aldol reaction is a nucleophilic addition in which an enolate is the nucleophile. Carbonyl Condensation Reactions Figure 24.1 The aldol reaction—An example of nucleophilic addition
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5 The Aldol Reaction A second example of an aldol reaction is shown with propanal as the starting material. The two molecules of the aldehyde that participate in the aldol reaction react in opposite ways. Carbonyl Condensation Reactions
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6 The Aldol Reaction These examples illustrate the general features of the aldol reaction. The α carbon of one carbonyl component becomes bonded to the carbonyl carbon of the other component. Carbonyl Condensation Reactions
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7 The Aldol Reaction—Dehydration of the Aldol Product Under the basic reaction conditions, the initial aldol product is often not isolated. Instead, it loses the elements of H 2 O from the α and β carbons to form an α , β -unsaturated carbonyl compound . Carbonyl Condensation Reactions
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The Aldol Reaction An aldol reaction is often called an aldol condensation because the β -hydroxy carbonyl compound that is initially formed loses H 2 O by dehydration. A condensation reaction is one in which a small molecule, in this case, H 2 O, is eliminated during the reaction. It may or may not be possible to isolate the β -hydroxy carbonyl compound under the conditions of the aldol reaction. When the α , β -unsaturated carbonyl compound is further conjugated with a carbon-carbon double bond or a benzene ring (as is the case in reaction 2), elimination of H 2 O is spontaneous and the β -hydroxy carbonyl compound cannot be isolated. Carbonyl Condensation Reactions
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Claisen reaction- Ester leaving group - Carbonyl...

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