Heterocyclic Compounds Quiz

Heterocyclic Compounds

• Heterocyclic compounds are cyclic hydrocarbons that contain one or more heteroatoms in a ring, which can be aromatic, partially or fully saturated. • Examples of heterocyclic compounds include nucleic acids, pharmaceuticals, agrochemicals, naturally occurring pigments, vitamins, and antibiotics.

Quinoline

• Quinoline is a heterocyclic aromatic organic compound with the chemical formula C₉H₇N, also known as benzo-pyridine or 1-aza-naphthalene. • Quinoline has a double ring structure composed of a benzene and a pyridine ring fused at two adjacent carbon atoms. • Physical properties of quinoline include a boiling point of 238°C, melting point of -15°C, density of 1.09 g/cm³ at 25°C, and solubility in hot water and most organic solvents.

Resonance Structures of Quinoline

• Quinoline shows aromatic properties due to its molecular orbital satisfying Huckle's rule (4n+2 rule). • The nitrogen lone pair is not released into the aromatic system, but is perpendicular to the p system. • The nitrogen withdraws electrons by resonance, resulting in an electron-deficient ring system.

Methods of Preparation

• Skraup synthesis: Quinoline can be synthesized by heating aniline with sulphuric acid, glycerol, and an oxidizing agent. • Combes Quinoline Synthesis: Quinoline can be synthesized by condensing unsubstituted anilines with β-diketones. • Friedländer Synthesis of Multisubstituted Quinolines: Quinoline can be synthesized by condensing o-amino benzaldehyde with acetaldehyde in the presence of an alkali. • Niementowski quinoline synthesis: Quinoline can be synthesized by reacting anthranilic acids with ketones or aldehydes. • Dobener Reaction: Quinoline can be synthesized by reacting an aniline with an aldehyde and pyruvic acid.

Chemical Reactions

• Basic Character: Quinoline is a slightly weaker base than pyridine and reacts with acids to form sparingly soluble salts. • Electrophilic Substitution Reaction: Quinoline undergoes electrophilic substitution reactions on the benzene ring, with the electrophile attacking positions 8 and 5. • Nucleophilic Substitution Reaction: Quinoline undergoes nucleophilic substitution reactions on the pyridine ring, reacting with Sodium Amide to form 2-Aminoquinoline.

Pharmaceutical and Medical Applications

• Quinoline has antimalarial, antibacterial, antifungal, anthelmintic, cardiotonic, anticonvulsant, anti-inflammatory, and analgesic activity. • Quinoline family compounds are used as a parent compound to make drugs, fungicides, and biocides, such as Chloroquine and hydroxychloroquine. • Quinaldine is used as an anti-malarial and in preparing other anti-malarial drugs. • Quinazoline is used as a chemical intermediate for making medicines and other organic compounds. • Quinoxaline is used as a chemical intermediate for making fungicides and other organic compounds. • Quinine is an anti-malarial natural product isolated from the bark of the Cinchona tree.

Heterocyclic Compounds

• Heterocyclic compounds are cyclic hydrocarbons that contain one or more heteroatoms in a ring, which can be aromatic, partially or fully saturated. • Examples of heterocyclic compounds include nucleic acids, pharmaceuticals, agrochemicals, naturally occurring pigments, vitamins, and antibiotics.

Quinoline

• Quinoline is a heterocyclic aromatic organic compound with the chemical formula C₉H₇N, also known as benzo-pyridine or 1-aza-naphthalene. • Quinoline has a double ring structure composed of a benzene and a pyridine ring fused at two adjacent carbon atoms. • Physical properties of quinoline include a boiling point of 238°C, melting point of -15°C, density of 1.09 g/cm³ at 25°C, and solubility in hot water and most organic solvents.

Resonance Structures of Quinoline

• Quinoline shows aromatic properties due to its molecular orbital satisfying Huckle's rule (4n+2 rule). • The nitrogen lone pair is not released into the aromatic system, but is perpendicular to the p system. • The nitrogen withdraws electrons by resonance, resulting in an electron-deficient ring system.

Methods of Preparation

• Skraup synthesis: Quinoline can be synthesized by heating aniline with sulphuric acid, glycerol, and an oxidizing agent. • Combes Quinoline Synthesis: Quinoline can be synthesized by condensing unsubstituted anilines with β-diketones. • Friedländer Synthesis of Multisubstituted Quinolines: Quinoline can be synthesized by condensing o-amino benzaldehyde with acetaldehyde in the presence of an alkali. • Niementowski quinoline synthesis: Quinoline can be synthesized by reacting anthranilic acids with ketones or aldehydes. • Dobener Reaction: Quinoline can be synthesized by reacting an aniline with an aldehyde and pyruvic acid.

Chemical Reactions

• Basic Character: Quinoline is a slightly weaker base than pyridine and reacts with acids to form sparingly soluble salts. • Electrophilic Substitution Reaction: Quinoline undergoes electrophilic substitution reactions on the benzene ring, with the electrophile attacking positions 8 and 5. • Nucleophilic Substitution Reaction: Quinoline undergoes nucleophilic substitution reactions on the pyridine ring, reacting with Sodium Amide to form 2-Aminoquinoline.

Pharmaceutical and Medical Applications

• Quinoline has antimalarial, antibacterial, antifungal, anthelmintic, cardiotonic, anticonvulsant, anti-inflammatory, and analgesic activity. • Quinoline family compounds are used as a parent compound to make drugs, fungicides, and biocides, such as Chloroquine and hydroxychloroquine. • Quinaldine is used as an anti-malarial and in preparing other anti-malarial drugs. • Quinazoline is used as a chemical intermediate for making medicines and other organic compounds. • Quinoxaline is used as a chemical intermediate for making fungicides and other organic compounds. • Quinine is an anti-malarial natural product isolated from the bark of the Cinchona tree.