Science, Part 85
Question 1: Discuss benzenes and reactions associated with them.
Answer 1: Benzene (C6H6) is an important cyclic organic compound. The electrons of its C atoms are delocalized resulting in combinations of single and double bonds, a structure which gives benzenes unusual stability. Compounds with strong, usually pleasant odors are often attached to benzene parents, so early chemists named these compounds aromatic compounds. Many benzene compounds have no odor, however. Common reactions include the following:Aromatic electrophilic substitution: the most important class of reactions associated with benzene. In these reactions one H atom of the benzene is replaced by an electrophile which can be an atom or, more often, a molecule or functional group. This class contains subclasses of reactions such as halogenation (benzene + a halogen), nitration (benzene + a nitrate), sulfonation (benzene + a sulfate), alkylation, and acylation.
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Question 2: Discuss amines and amides and reactions associated with them.
Answer 2: Amines (R—NH2) are a functional group containing nitrogen which form compounds vital to biological processes. They from when a hydrogen from an ammonia molecule (NH3) is replaced by an organic compound. They can be primary, secondary, or tertiary amines, depending on how many atoms are bonded to the N atom. Amines react with acyl chlorides (Cl—C=O) and acid anhydrides in nucleophilic substitution, producing amides. They neutralize carboxylic acid in an acid-base reaction to produce ammonium carboxylate. Tertiary amines react with strong halogen acids to form ammonium salts. Amides (O=C—N) are another functional group; the most important of their reactions is hydrolysis in which the addition of water severs the C—N bond to create amine and carboxylic acid.
Question 3: Discuss esters and reactions associated with them.
Answer 3: Esters (O=C—O) are a functional group often derived from carboxylic acids from which a H atom has been removed. This process is usually a condensation reaction in which two hydrogen-containing groups or compounds react, joining their H and releasing it as water. Such condensation reactions that produce an ester are called esterification reactions. The most important class of reactions associated with esters is hydrolysis, a reaction in which the ester is broken down by water to yield an alcohol and a carboxylic acid or salt. Hydrolysis of esters may be catalyzed by an acid or a base; if the catalyst is a base, the process if called saponification. Esters may also form amides through a reaction with primary or secondary amines at high temperatures.
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