lecture 15 - 15. Benzene and Aromaticity Based on McMurry's...

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15. Benzene and Aromaticity Based on McMurry’s Organic Chemistry , 7 th edition
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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
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3 Why this Chapter? Reactivity of substituted aromatic compounds is tied to their structure Aromatic compounds provide a sensitive probe for studying relationship between structure and reactivity
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4 15.1 Sources and Names of Aromatic Hydrocarbons From high temperature distillation of coal tar Heating petroleum at high temperature and pressure over a catalyst
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5 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
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6 The Phenyl Group When a benzene ring is a substituent, the term phenyl is used (for C 6 H 5 5 ) You may also see “Ph” or “ φ ” in place of “C 6 H 5 Benzyl ” refers to “C 6 H 5 CH 2 5 ”
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7 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”)
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8 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)
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9 15.2 Structure and Stability of Benzene: Molecular Orbital Theory Benzene reacts 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
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This note was uploaded on 09/06/2009 for the course CHEM chem 12 AB taught by Professor Adamczeski during the Spring '09 term at San Jose City College.

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lecture 15 - 15. Benzene and Aromaticity Based on McMurry's...

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