Kingdom of saudi arabia Ministry of higher education

Kingdom of saudi arabia Ministry of higher education Tabuk University Faculty of science- Girls section Chemistry department Six-Member Ring contain Nitrogen Atom Dr. Nadia Hussein Elsayed.

Pyridine

Definition of Pyridine l Six member ring contain nitrogen atom lchemical formula l C 5 H 5 N l Molecular formula of pyridine like molecular formula of benzene but we replace carbon atom( CH) in benzene with nitrogen atom

pyridine synthesis

Hantzsch pyridine synthesis β-keto ester dihydropyridine The Hantzsch dihydropyridine synthesis is found to benefit from microwave chemistry

PYRIDINES Synthesis of Pyridines From 1, 5 -dicarbonyl and ammonia (c. f. chapt. 3) From 1, 3 -dicarbonyl and enamine (c. f. chapt. 3) From 2 equivs. 1, 3 -dicarbonyl , aldehyde and ammonia - Hantzsch Synthesis Various syntheses from other heterocycles

Resonances of Pyridine

Electrophilic Substitution of Pyridine

Electrophilic Substitution of Pyridine No reaction of fredial craft l

Electrophilic Substitution of Pyridine

Electrophilic Substitution of Pyridine

4. Chemistry of pyridine Electrophilic substitution in pyridine Pyridine is less active, than benzene toward electrophilic agents, because nitrogen is more electronegative, than carbon and acts like an electron withdrawing substituent, including the meta-directing effect. Example:

Nucleophilic substitution in pyridine The presence of nitrogen enables pyridine to react with nucleophilic agents, like an electron withdrawing substituents enables benzene to participate in such reactions, including the ortho-directing effect.

Another example: These reactions require very strong nucleophiles and heat, because H- is a very weak leaving group. In ortho- or para-substituted pyridines nucleophilic substitution proceeds much easier.

Tautomerism of 2 -pyridones Unlike phenol, 2 -hydroxypyridine prefers the carbonyl form (2 -pyridone), because the isomerisation does not break aromaticity. However, 2 -aminopyridine is the preferred isomer due to the strong conjugation between electron donating amino-group and electron withdrawing pyridine ring and weaker conjugation in 2 -pyridoneimine

Pyridinium salts