Chapter15 - 15. Benzene and Aromaticity Based on...

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Unformatted text preview: 15. Benzene and Aromaticity Based on McMurry’s Organic Chemistry , 6 th edition ©2003 Ronald Kluger Department of Chemistry University of Toronto McMurry Organic Chemistry 6th edition Ch 15 (c) 2003 2 Aromatic Compounds Aromatic was used to described some fragrant compounds in early 19 th century Not correct: later they are grouped by chemical behavior (unsaturated compounds that undergo substitution rather than addition) Current: distinguished from aliphatic compounds by electronic configuration McMurry Organic Chemistry 6th edition Ch 15 (c) 2003 3 15.1 Sources of Aromatic Hydrocarbons From high temperature distillation of coal tar Heating petroleum at high temperature and pressure over a catalyst McMurry Organic Chemistry 6th edition Ch 15 (c) 2003 4 15.2 Naming Aromatic Compounds Many common names (toluene = methylbenzene; aniline = aminobenzene) Monosubstituted benzenes systematic names as hydrocarbons with – benzene C 6 H 5 Br = bromobenzene C 6 H 5 NO 2 = nitrobenzene, and C 6 H 5 CH 2 CH 2 CH 3 is propylbenzene McMurry Organic Chemistry 6th edition Ch 15 (c) 2003 5 The Phenyl Group When a benzene ring is a substituent, the term phenyl is used (for C 6 H 5 ) You may also see “Ph” or “ φ ” in place of “C 6 H 5 ” “ Benzyl ” refers to “C 6 H 5 CH 2 ” McMurry Organic Chemistry 6th edition Ch 15 (c) 2003 6 Disubstituted Benzenes Relative positions on a benzene ring ortho- (o) on adjacent carbons (1,2) meta- (m) separated by one carbon (1,3) para- (p) separated by two carbons (1,4) Describes reaction patterns (“occurs at the para position”) McMurry Organic Chemistry 6th edition Ch 15 (c) 2003 7 Naming Benzenes With More Than Two Substituents Choose numbers to get lowest possible values List substituents alphabetically with hyphenated numbers Common names, such as “toluene” can serve as root name (as in TNT) McMurry Organic Chemistry 6th edition Ch 15 (c) 2003 8 15.3 Structure and Stability of Benzene Benzene reacts with slowly with Br 2 to give bromobenzene (where Br replaces H) This is substitution rather than the rapid addition reaction common to compounds with C=C, suggesting that in benzene there is a higher barrier McMurry Organic Chemistry 6th edition Ch 15 (c) 2003...
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Chapter15 - 15. Benzene and Aromaticity Based on...

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