11. Carbonyl compounds (aldehydes and ketones). Reactivity of α -carbon atom-tautomerism, aldol condensation-examples in living systems. Cannizzaro reaction, oxidation of carbonyl compounds. Substitution reactions. Biologically active substances with carbonyl group-coenzyme Q, K vitamins, camphorquinone, glycerolaldehyde, 11-cis retinal. Ketone bodies.

Reaction of carbonyl compounds with carbon nucleophiles (aldol reaction and aldol condensation).

• The aldol reaction involves the reaction of carbonyl compounds (aldehydes or ketones) with carbon nucleophiles to form β-hydroxycarbonyl compounds (aldol products).

• It occurs in three main steps:
• 1. Nucleophile Formation:
• A base (e.g., NaOH, NaOEt) abstracts a proton from the α-carbon of the carbonyl compound, forming an enolate ion.
• 2. Nucleophilic Addition:
• The enolate ion attacks the electrophilic carbonyl carbon of another carbonyl molecule, forming a tetrahedral intermediate.
• 3. Condensation (Optional):
• In the presence of a weak base or under acidic conditions, the aldol product can undergo dehydration, yielding a conjugated enone. This step is aldol condensation.

Role for biological processes.

• The aldol reaction is a pivotal process in biological systems, facilitating the formation of carbon-carbon (C-C) bonds.
• It is predominantly involved in carbohydrate metabolism within living organisms.
• Enzymes known as aldolases catalyze aldol reactions, aiding in the synthesis of complex molecules.
• Aldol products generated through this reaction serve as crucial intermediates in various biosynthetic pathways.
• These intermediates contribute to the production of sugars, amino acids, and other biomolecules vital for cellular functions.
• Thus, the aldol reaction plays a fundamental role in driving the synthesis of essential molecules necessary for cellular structure, energy production, and regulatory processes.