CHAPTER ELEVEN Arenes and Aromaticity Higher level molecular orbital theory can provide quantitative information about orbital energies and how strongly a molecule holds its electrons. When one compares aromatic and nonaromatic species in this way, it is found that cyclic delocalization causes the T electrons of benzene to be more strongly bound(more stable) than they would be if restricted to a system with alternating single and double bonds We'll come back to the molecular orbital description of benzene later in this chap- ter(Section 11. 19)to see how other conjugated polyenes compare with benzene. 11.7 SUBSTITUTED DERIVATIVES OF BENZENE AND THEIR NOMENCLATURE All compounds that contain a benzene ring are aromatic, and substituted derivatives of benzene make up the largest class of aromatic compounds. Many such compounds ar named by attaching the name of the substituent as a prefix to benzene C(CH3) Bromobenzene tert-Butylbenzene Ni Many simple monosubstituted derivatives of benzene have common names of long stand ing that have been retained in the IUPAC system. Table 11. 1 lists some of the most Important ones. Dimethyl derivatives of benzene are called xylenes. There are three xylene isomers the ortho(o)" meta(m)-,and para(p)-substituted derivatives 3 o-Xylene m-Xylene Xylene (1, 2-dimethylbenzene) (1, 3-dimethylbenzene) (1, 4-dimethylben The prefix ortho signifies a 1, 2-disubstituted benzene ring, meta signifies 1, 3-disubstitu- tion, and para signifies 1, 4-disubstitution. The prefixes o, m, and p can be used when a substance is named as a benzene derivative or when a specific base name(such as ace- tophenone) is used. For example, O O-Dichlorobenzene IN-Nitrotoluene Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteHigher level molecular orbital theory can provide quantitative information about orbital energies and how strongly a molecule holds its electrons. When one compares aromatic and nonaromatic species in this way, it is found that cyclic delocalization causes the electrons of benzene to be more strongly bound (more stable) than they would be if restricted to a system with alternating single and double bonds. We’ll come back to the molecular orbital description of benzene later in this chap￾ter (Section 11.19) to see how other conjugated polyenes compare with benzene. 11.7 SUBSTITUTED DERIVATIVES OF BENZENE AND THEIR NOMENCLATURE All compounds that contain a benzene ring are aromatic, and substituted derivatives of benzene make up the largest class of aromatic compounds. Many such compounds are named by attaching the name of the substituent as a prefix to benzene. Many simple monosubstituted derivatives of benzene have common names of long stand￾ing that have been retained in the IUPAC system. Table 11.1 lists some of the most important ones. Dimethyl derivatives of benzene are called xylenes. There are three xylene isomers, the ortho (o)-, meta (m)-, and para ( p)- substituted derivatives. The prefix ortho signifies a 1,2-disubstituted benzene ring, meta signifies 1,3-disubstitu￾tion, and para signifies 1,4-disubstitution. The prefixes o, m, and p can be used when a substance is named as a benzene derivative or when a specific base name (such as ace￾tophenone) is used. For example, Cl Cl o-Dichlorobenzene (1,2-dichlorobenzene) NO2 CH3 m-Nitrotoluene (3-nitrotoluene) C F O CH3 p-Fluoroacetophenone (4-fluoroacetophenone) CH3 CH3 o-Xylene (1,2-dimethylbenzene) CH3 CH3 m-Xylene (1,3-dimethylbenzene) CH3 CH3 p-Xylene (1,4-dimethylbenzene) Br Bromobenzene C(CH3)3 tert-Butylbenzene NO2 Nitrobenzene 406 CHAPTER ELEVEN Arenes and Aromaticity Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website