14. Hydroxycarboxilic acids and ketocarboxylic acids – overview. Comparison of their chemical properties. Important compounds of this group and their biological significance – lactic acid, salicylic acid, malic acid, tartaric acid, citric acid; pyruvic acid, acetoacetic acid, oxaloacetic acid, α -ketoglutaric acid. Ketone bodies.

Hydroxycarboxylic acids (aliphatic and aromatic acids).

• Definition:
• Hydroxycarboxylic acids contain both a hydroxyl group (-OH) and a carboxyl group (-COOH) in their structure.
• Classification:
• 1. Aliphatic Hydroxycarboxylic Acids:
• Can be further categorized into:
• Saturated: No carbon-carbon double bonds.
• Unsaturated: Contain one or more carbon-carbon double bonds.
• 2. Aromatic Hydroxycarboxylic Acids:
• Contain an aromatic ring in their structure along with -OH and -COOH groups.
• Examples:
• Saturated Aliphatic: Lactic acid
• Unsaturated Aliphatic: Citric acid
• Aromatic: Salicylic acid
• Sources:
• Found naturally in fruits, vegetables, and microorganisms.
• Applications:
• Used in food, pharmaceuticals, cosmetics, and chemical synthesis.

Stereoisomerism in saturated hydroxy carboxylic acids.

• L-lactic acid is the L stereoisomer, commonly found in the L-form in biological systems and is often produced during anaerobic respiration in muscle cells. Hence, it's often referred to as "L-muscle."D-lactic acid is the D stereoisomer, and it's found in D-form in certain fermented dairy products like milk. Hence, it's often referred to as "D-milk." These terms, L and D, denote the configuration of the asymmetric carbon atom in the molecule. L refers to the "levorotatory" configuration (meaning it rotates plane-polarized light counterclockwise), while D refers to the "dextrorotatory" configuration (rotating plane -polarized light clockwise). The L and D forms are not related to the terms "left" and "right" but rather originate from Latin terms for "left" and "right" handedness in terms of optical activity.