Nucleophilic Addition of carbonyl compounds.pptx

Nucleophilic addition is the most important reaction of carbonyls. Not just aldehydes and ketones, but also carboxylic acid derivatives in general.

Carbonyls undergo addition reactions with a large range of nucleophiles.
Comparing the relative basicity of the nucleophile and the product is extremely helpful in determining how reversible the addition reaction is. Reactions with Grignards and hydrides are irreversible. Reactions with weak bases like halides and carboxylates generally don’t happen.
Electronic effects (inductive effects, electron donation) have a large impact on reactivity.
Large groups adjacent to the carbonyl will slow the rate of reaction.
Neutral nucleophiles can also add to carbonyls, although their additions are generally slower and more reversible. Acid catalysis is sometimes employed to increase the rate of addition.

1. NUCLEOPHILIC ADDITION REACTION A Nucleophilic addition reaction is a chemical addition reaction in which a nucleophile forms a sigma bond with an electron deficient species. These reaction enable a conversion of carbonyl groups into variety of function group. Aldehydes and ketones give two type of nucleophilic addition reaction. They are: Simple without elimination nucleophile reactions.With sodium bisulphite , Grignard, HCN and Alcohol Nucleophilic addition reactions followed by elimination . This reaction is involved by elimination of water molecule. In which first is Reaction with ammonia Derivatives Reaction with ammonia.

2. ADDITION OF GRIGNARD REAGENT Grignard reagent are strong nucleophile, they add readily to aldehydes and ketones to form addition products which form alcohols.

3. ELIMINATION OF WATER MOLECULE REACTION WITH AMMONIA DERIVATIVES Aldehydes and ketones undergo nucleophilic addition reaction with a number of ammonia derivatives such as hydroxylamine, hydrazine in weakly acidic medium to form addition products which automatically lose a molecule of water to form compound containing C=N group. Example:

4. MECHANISM

5. REACTION WITH AMINE Most of the aldehydes react with ammonia to form addition products called aldehyde- ammonias. These products are unstable and immediately lose a molecule of water to form aldimines which subsequently undergo polymerization . Benzaldehyde reacts with ammonia to form a complex product called hydrobenzamide .

6. ADDITION OF SODIUM BISULPHITE Carbonyl compounds form crystalline adducts with sodium bisulphite .

7. MECHANISM It involves nucleophilic addition at carbonylic carbon Since S is the more nucleophilic site than O , therefore a C- S rather than C-O bond is formed in the adduct. Also, SO 3 - -- is a large ion and reacts only if C=O group is not sterically hindered , as in the case of aldehydes, methyl ketones and cyclic ketones .

8. ADDITION OF WATER Water ( H-O-H) is a typical nucleophile and adds reversibly to a carbonyl compound to form a gem – diol ( hydrate). The germ diol are too unstable to be isolated. However, the UV and IR data have given proof about the formation of gem – diols in these reaction.

9. ADDITION OF HCN Aldehydes and ketones and hydrogen cyanide to give corresponding cyanohydrins. These are important intermediates in the prepration of hydroxy acid.

10. Mechanism It involves addition of cyanide (nucleophile) followed by addition of hydrogen .

11. ADDITION OF ALCOHOL Aldehydes give acetals , when treated with alcohols in the presence of anhydrous acids. These acetals can regenerate aldehydes o n treatment with acids and hence its use to protect- CHO group. MECHANISM It involves three steps, addition of proton. Nucleophilic addition of R‘OH and disprotonation to give hemiacetal . Hemiacetal follows same steps further to give acetal .

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