Download Amines and Heterocyclic Compounds: Properties, Nomenclature, and Reactions - Prof. Yian Sh and more Study notes Organic Chemistry in PDF only on Docsity! 23 March Amines are compounds in which one or more of the hydrogens of ammonia (NH3) have been replaced by an alkyl group. Heterocyclic compounds (heterocycles) are cyclic compounds in which one or more of the atoms of the ring are hetero atoms. Heterocycles make up an exceedingly important class of compounds. Almost all the compounds we know as drugs, most vitamins, and many other natural products are heterocycles. Hetero atom is an atom other than carbon, such as N, O, S, Se, P, Si, B, and As. More about amine nomenclature Common names for amines are obtained by citing the names of the alkyl substituents (alphabetically) that have replaced the hydrogens of NH3. Systematic names use “amine” as a functional group suffix. Saturated Heterocycles Do not contain double bonds A saturated heterocycle is easily named as a cycloalkane using a prefix to denote the hetero atom (“aza” for N; “oxa” for O; “thia” for S). Reaction of Amines Amine can act both as base and nucleophile. Synthesis of Amines Gabriel synthesis Aromatic five-membered-ring heterocycles Ex. pyrrole, furan, and thiophene Pyrrole is an extremely weak base because nitrogen’s nonbonding pair of electrons is needed for pyrrole’s aromaticity. Pyrrole, furan, and thiophene undergo electrophilic substitution at C-2 Substitution occurs preferentially at C-2 because the intermediate obtained by putting a substituent at this position is more stable than the intermediate obtained by putting a substituent at C-3 If both position adjacent to the hetero atom are occupied, electrophilic substitution will take place at C-3 Pyrrole, furan, and thiophene are more reactive than benzene toward electrophilic substitution Benzene requires a relatively strong Lewis acid for electrophilic aromatic substation; thiophene needs a weak Lewis acid SnCl4; furan requires an even weaker Lewis acid BF3; and pyrroles require no catalyst in this case. When pyrrole is protonated, it is not protonated on nitrogen; it is protonated on C-2. Pyrrole is unstable in strongly acidic solutions because it polymerizes readily. Indole, benzofuran, and benzothipohene contain a five-membered aromatic ring fused with a benzene ring. Pyridine is a tertiary amine and undergoes reactions characteristic of tertiary amines. Like benzene, pyridine is aromatic and undergoes electrophilic aromatic substitution reactions. Pyridine’s electron-withdrawing nitrogen causes the ring carbons to have significantly less electron density than the ring carbons of benzene. Pyridine undergoes electrophilic aromatic substation reactions only under vigorous conditions, and the yields of these reactions are often quite low. Pyridine undergoes electrophilic substitution at C-3.
