Chapter 12. Summary

Nomenclature. Compounds containing double or triple bonds between carbon atoms are said to be unsaturated. The alkenes contain double bonds and the alkynes contain triple bonds. In the lUPAC nomenclature system, alkene names end in -ene and the alkynes end in -yne.

Geometry of Alkenes. In alkenes, the double-bonded carbons and the four groups attached to these carbons lie in the same plane. Because rotation about the double bond is restricted, alkenes may exist as geometric or cis-trans isomers. This type of stereoisomerism is possible when each double-bonded carbon is attached to two different groups.

Physical properties of Alkenes. The physical properties of alkenes are very similar to those of the alkanes. They are nonpolar, insoluble in water, less dense than water, and soluble in nonpolar solvents.

Alkene Reactions. Alkenes are chemically quite reactive, and their characteristic reaction is addition to the double bond. Three important addition reactions are: bromination (an example of halogenation) to give a dibrominated alkane, hydration to produce an alcohol, and the reaction with H-X to give an alkyl halide. The addition of H2O and H-X are governed by Markovnikov's rule.

Addition polymers. Addition polymers are formed from alkene monomers which undergo repeated addition reactions with each other. Many familiar and widely used materials, such as fibers and plastics, are addition polymers.

Alkynes. The alkynes contain triple bonds and possess a linear geometry of the two carbons and the two attached groups. Alkyne names end in -yne. The physical and chemical properties of alkynes are very similar to those of the alkenes.

Aromatic Compounds and the Benzene Structure. Benzene, the simplest aromatic compound, and other members of the aromatic class contain a six membered ring. This aromatic ring is often drawn as a hexagon containing a circle which represents the six electrons of three double bonds that move freely around the ring. All organic compounds that do not contain an aromatic ring are called aliphatic compounds.

Nomenclature of Benzene derivatives. Several acceptable lUPAC names are possible for many benzene compounds. Some lUPAC names are based upon widely used common names, such as toluene and aniline. Other compounds are named as derivatives of benzene or by designating the benzene ring as a phenyl group.

Properties and Uses of Aromatic Compounds. Aromatic hydrocarbons are nonpolar and have physical properties similar to the alkanes and alkenes. Benzene resists addition reactions typical of alkenes. Benzene and toluene are key industrial chemicals. Other important aromatics include phenol, aniline, and styrene.