1. Explain the mechanism of nucleophilic addition reaction of aldehydes and ketones with hydrogen cyanide.
Answer: The nucleophilic addition reaction of aldehydes and ketones with hydrogen cyanide involves the attack of the cyanide ion (CN-) on the carbonyl carbon of the aldehyde or ketone. This attack is facilitated by the presence of a Lewis acid catalyst, such as HCl or ZnCl2. The cyanide ion acts as a nucleophile, attacking the electrophilic carbonyl carbon, resulting in the formation of a cyanohydrin. The reaction proceeds through the formation of an intermediate, in which the carbonyl oxygen coordinates with the Lewis acid catalyst. This coordination activates the carbonyl carbon, making it more susceptible to nucleophilic attack. The resulting cyanohydrin can be hydrolyzed to yield a carboxylic acid or can undergo further reactions to form a variety of organic compounds.
2. Discuss the factors influencing the acidity of carboxylic acids.
Answer: The acidity of carboxylic acids is influenced by several factors. Firstly, the presence of the carboxyl group (-COOH) imparts acidity to the molecule. The carboxyl group contains two electronegative oxygen atoms, which can stabilize the negative charge on the carboxylate ion formed after the loss of a proton. This stabilization is due to resonance, where the negative charge is delocalized between the two oxygen atoms. Secondly, the presence of electron-withdrawing groups attached to the carboxyl group increases the acidity of carboxylic acids. These groups, such as halogens or nitro groups, pull electron density away from the carboxyl group, making it more acidic. Conversely, the presence of electron-donating groups decreases the acidity of carboxylic acids. Thirdly, the size of the alkyl groups attached to the carboxyl group also affects acidity. Larger alkyl groups destabilize the carboxylate ion due to steric hindrance, making the carboxylic acid less acidic.
3. Explain the mechanism of the reaction between carboxylic acids and alcohols to form esters.
Answer: The reaction between carboxylic acids and alcohols to form esters is known as esterification. This reaction involves the condensation of the carboxylic acid and alcohol, with the elimination of a water molecule. The reaction is typically catalyzed by an acid, such as sulfuric acid or hydrochloric acid. The acid protonates the carbonyl oxygen of the carboxylic acid, making it more susceptible to nucleophilic attack by the alcohol. The alcohol acts as a nucleophile, attacking the electrophilic carbonyl carbon of the carboxylic acid. This results in the formation of a tetrahedral intermediate, which then undergoes a proton transfer to form an alkoxycarboxylic acid. Finally, the alkoxycarboxylic acid loses a water molecule, resulting in the formation of the ester. The overall reaction can be represented as follows: Carboxylic acid + Alcohol → Ester + Water.
4. Discuss the reactions of aldehydes and ketones with Tollens’ reagent.
Answer: Tollens’ reagent, also known as silver mirror reagent, is used to distinguish aldehydes from ketones. It is a solution of silver nitrate (AgNO3) in aqueous ammonia (NH3). When Tollens’ reagent is added to an aldehyde, it undergoes a redox reaction, resulting in the formation of a silver mirror on the inner surface of the reaction vessel. This reaction involves the oxidation of the aldehyde to a carboxylic acid and the reduction of silver ions to metallic silver. The reaction proceeds through the formation of a complex between the aldehyde and the silver ion, followed by the reduction of the silver ion by the aldehyde. Ketones, on the other hand, do not undergo this reaction as they lack the necessary hydrogen atom to reduce the silver ion. Therefore, when Tollens’ reagent is added to a ketone, no silver mirror is formed.
5. Explain the mechanism of the reaction between aldehydes and ketones with Grignard reagents.
Answer: The reaction between aldehydes and ketones with Grignard reagents is known as the Grignard reaction. This reaction involves the nucleophilic addition of the carbon atom of the Grignard reagent to the carbonyl carbon of the aldehyde or ketone. The reaction proceeds through the formation of an alkoxide intermediate, in which the carbonyl oxygen coordinates with the magnesium atom of the Grignard reagent. This coordination activates the carbonyl carbon, making it more susceptible to nucleophilic attack. The resulting alkoxide intermediate can then undergo protonation to yield the corresponding alcohol. The overall reaction can be represented as follows: Aldehyde/Ketone + Grignard reagent → Alcohol.
6. Discuss the mechanism of the reaction between aldehydes and ketones with sodium bisulfite.
Answer: The reaction between aldehydes and ketones with sodium bisulfite is known as the bisulfite addition reaction. This reaction involves the addition of the bisulfite ion (HSO3-) to the carbonyl group of the aldehyde or ketone. The reaction proceeds through the formation of a cyclic intermediate, in which the bisulfite ion attacks the carbonyl carbon, resulting in the formation of a sulfonic acid derivative. This intermediate can then undergo further reactions, such as oxidation or reduction, depending on the conditions. The overall reaction can be represented as follows: Aldehyde/Ketone + Sodium bisulfite → Sulfonic acid derivative.
7. Explain the mechanism of the reaction between aldehydes and ketones with hydroxylamine.
Answer: The reaction between aldehydes and ketones with hydroxylamine is known as the oxime formation reaction. This reaction involves the nucleophilic addition of the nitrogen atom of hydroxylamine to the carbonyl carbon of the aldehyde or ketone. The reaction proceeds through the formation of an intermediate, in which the carbonyl oxygen coordinates with the nitrogen atom of hydroxylamine. This coordination activates the carbonyl carbon, making it more susceptible to nucleophilic attack. The resulting intermediate can then undergo protonation to yield the corresponding oxime. The overall reaction can be represented as follows: Aldehyde/Ketone + Hydroxylamine → Oxime.
8. Discuss the reactions of aldehydes and ketones with primary amines to form imines.
Answer: The reaction between aldehydes and ketones with primary amines is known as the imine formation reaction. This reaction involves the nucleophilic addition of the nitrogen atom of the primary amine to the carbonyl carbon of the aldehyde or ketone. The reaction proceeds through the formation of an intermediate, in which the carbonyl oxygen coordinates with the nitrogen atom of the primary amine. This coordination activates the carbonyl carbon, making it more susceptible to nucleophilic attack. The resulting intermediate can then undergo protonation to yield the corresponding imine. The overall reaction can be represented as follows: Aldehyde/Ketone + Primary amine → Imine.
9. Explain the mechanism of the reaction between aldehydes and ketones with hydrazine.
Answer: The reaction between aldehydes and ketones with hydrazine is known as the hydrazone formation reaction. This reaction involves the nucleophilic addition of the nitrogen atom of hydrazine to the carbonyl carbon of the aldehyde or ketone. The reaction proceeds through the formation of an intermediate, in which the carbonyl oxygen coordinates with the nitrogen atom of hydrazine. This coordination activates the carbonyl carbon, making it more susceptible to nucleophilic attack. The resulting intermediate can then undergo protonation to yield the corresponding hydrazone. The overall reaction can be represented as follows: Aldehyde/Ketone + Hydrazine → Hydrazone.
10. Discuss the mechanism of the reaction between aldehydes and ketones with semicarbazide.
Answer: The reaction between aldehydes and ketones with semicarbazide is known as the semicarbazone formation reaction. This reaction involves the nucleophilic addition of the nitrogen atom of semicarbazide to the carbonyl carbon of the aldehyde or ketone. The reaction proceeds through the formation of an intermediate, in which the carbonyl oxygen coordinates with the nitrogen atom of semicarbazide. This coordination activates the carbonyl carbon, making it more susceptible to nucleophilic attack. The resulting intermediate can then undergo protonation to yield the corresponding semicarbazone. The overall reaction can be represented as follows: Aldehyde/Ketone + Semicarbazide → Semicarbazone.