Organic Chemistry Heterocyclic Compounds Lec.2 PDF

Organic Chemistry III Heterocyclic Compounds Six-membered ring system | Lec.2 Organic Chemistry | Heterocyclic Compounds Contents : Heterocyclic systems 3 Organic Chemistry | Heterocyclic Compounds Heterocyclic systems: A heterocyclic compound is one that contains a ring made up of more than one kin...

Organic Chemistry III Heterocyclic Compounds Six-membered ring system | Lec.2 Organic Chemistry | Heterocyclic Compounds Contents : Heterocyclic systems 3 Organic Chemistry | Heterocyclic Compounds Heterocyclic systems: A heterocyclic compound is one that contains a ring made up of more than one kind of atom. In most of the cyclic compounds that we have studied so far benzene, naphthalene, cyclohexanol , cyclopentadiene the rings are made up only of carbon atoms; such compounds are called homocyclic or alicyclic compounds. But there are also rings containing, in addition to carbon, other kinds of atoms, most commonly nitrogen, oxygen, or sulfur. For example: Organic Chemistry | Heterocyclic Compounds We notice that in numbering the ring position, heteroatoms are generally given the lowest possible numbers: Organic Chemistry | Heterocyclic Compounds Organic Chemistry | Heterocyclic Compounds Numerous heterocyclic compounds have been encountered for example: Cyclic anhydrides and cyclic imides like: Succinic anhydride and phthalimide Note: In all these, the chemistry is essentially that of their open chain analogs. Organic Chemistry | Heterocyclic Compounds Cyclic esters and cyclic amides: Lactones Lactams Organic Chemistry | Heterocyclic Compounds Cyclic acetals of dihydroxy alcohols like: The solvents dioxane and tetrahydrofuran Note: In all these, the chemistry is essentially that of their open chain analogs. Organic Chemistry | Heterocyclic Compounds Three membered heterocyclic rings which, because of ring strain, are highly reactive like: Epoxides and aziridines Organic Chemistry | Heterocyclic Compounds The fleeting but important intermediates like cyclic halonium ions and cyclic sulfonium ions. Organic Chemistry | Heterocyclic Compounds Heterocyclic intermediates are being used more and more in synthesis as protecting groups, readily generated and, when their job is done, readily removed. We have seen two examples of this: The temporary incorporation of the carboxyl group into a 2 oxazoline ring. Organic Chemistry | Heterocyclic Compounds And the temporary formation of tetrahydropyranyl (THP) esters, resistant toward alkali but extremely easily cleaved by acid. Carboxyl groups are often masked by reaction with dihydropyran , which yields esters that are stable toward base but easily hydrolyzed by dilute aqueous acids. Organic Chemistry | Heterocyclic Compounds In the biological world, the heterocyclic compounds are everywhere. Carbohydrates are heterocyclic. So are chlorophyll and hemin which make leaves green and blood red and bring life to plants and animals. Heterocycles form the sites of reaction in many enzymes and coenzymes. Heredity comes down, ultimately, to the particular sequence of attachment of a half dozen heterocyclic rings to the long chains of nucleic acids. Organic Chemistry | Heterocyclic Compounds Organic Chemistry | Heterocyclic Compounds We can take up only a very few of the many different heterocyclic systems and look only briefly at them. Among the most important and most interesting heterocycles are the ones that possess aromatic properties We shall focus our attention on a few of these, and in particular upon their aromatic properties. Organic Chemistry | Heterocyclic Compounds We can get some idea of the importance as well as complexity of heterocyclic systems from the following examples: Some others are hemin. Nicotinamide Adenine dinucleotide and oxytocin Organic Chemistry | Heterocyclic Compounds