Aldehyde Ketone and Carboxylic acid Short notes

 Aldehyde Ketone and Carboxylic acid Short notes

Aldehydes, Ketones and Carboxylic Acids (Chapter 12, NCERT Class 12 Chemistry)

This chapter covers three important functional groups of organic compounds: aldehydes, ketones, and carboxylic acids. It delves into their structure, preparation, properties, and reactions.

1. Structure and Nomenclature:

• Aldehydes contain a carbonyl group (C=O) with a hydrogen atom attached to it (R-CHO).
• Ketones have a carbonyl group with two carbon atoms attached to it (R-CO-R').
• Carboxylic acids contain a carbonyl group bonded to a hydroxyl group (-OH), forming a carboxyl group (R-COOH).
• The chapter covers IUPAC nomenclature for these functional groups.

2. Preparation Methods:

• Aldehydes: Oxidation of primary alcohols, reduction of acyl chlorides, dehydrogenation of primary alcohols.
• Ketones: Oxidation of secondary alcohols, Friedel-Crafts acylation reaction.
• Carboxylic Acids: Oxidation of primary or secondary alcohols, hydrolysis of esters or amides, carboxylic acid derivatives (acid chlorides, anhydrides).

3. Physical Properties:

• Due to the presence of the carbonyl group, aldehydes and ketones exhibit hydrogen bonding, leading to higher boiling points compared to similar-sized hydrocarbons.
• Carboxylic acids have even higher boiling points due to stronger hydrogen bonding between the carboxyl group and OH groups of other carboxylic acid molecules.

4. Chemical Reactions:

Aldehydes and Ketones:

• Nucleophilic addition reactions: Due to the electrophilic nature of the carbonyl carbon, aldehydes and ketones react with nucleophiles (electron-donating species). Examples include addition of water (hydration), alcohols (hemiacetal and acetal formation), ammonia and its derivatives (imine and enamine formation).
• Oxidation: Aldehydes are easily oxidised to carboxylic acids. Ketones are resistant to further oxidation under normal conditions.
• Reduction: Aldehydes and ketones can be reduced to primary and secondary alcohols, respectively.
• Haloform reaction: Aldehydes with a methyl group adjacent to the carbonyl group undergo this reaction with a trihalogenomethane and strong base to form a carboxylic acid and a haloform.

Carboxylic Acids:

• Acidic character: Carboxylic acids are weak acids due to the ability of the carboxyl group to donate a proton (H+). They react with bases to form salts.
• Esterification: Reaction with alcohols in the presence of an acid catalyst to form esters.
• Amide formation: Reaction with ammonia or amines to form amides.
• Decarboxylation: Removal of carbon dioxide (CO2) under certain conditions.

5. Important Named Reactions:

• Cannizzaro reaction: Self-oxidation and reduction reaction of aldehydes lacking an alpha-hydrogen (hydrogen on the carbon next to the carbonyl group) to form an alcohol and a carboxylic acid.
• Aldol condensation: Condensation reaction between two aldehydes or an aldehyde and a ketone with a base catalyst to form a beta-hydroxy aldehyde or ketone.
• Claisen condensation: Similar to aldol condensation but uses esters instead of aldehydes or ketones.
• Hell-Volhard-Zelinsky reaction: Halogenation of a carboxylic acid alpha-carbon to a keto acid.

The chapter also covers the uses of these functional groups in various applications.

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