Chapter 11

Chapter 11 - Chapter 11 Arenes and Aromaticity I Benzenea...

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Chapter 11- Arenes and Aromaticity I. Benzene- a. Molecular formula of benzene (C 6 H 6 ) suggests that it is unsaturated and can undergo addition reactions, yet since it is special substitution occurs when reacts with Br 2 in the presence of iron (III) Bromide catalyst b. It resulted in only 1 monobromination product of benzene, suggesting that all Hs are equivalent. c. Structure- i. Benzene is C 6 H 6 ii. All the hydrogen’s of benzene are equivalent iii. The structural theory requires that there be four bonds to each C d. Benzene is planar and its C skeleton has the shape of a regular hexagon. All the C-C bonds are equal lengths and have 120 ° bond angles that correspond to sp 2 hybridization. e. Kekule structures- two resonance forms of benzene that have different double bond locations. The two forms are representation of the benzene ring but neither is correct. i. A hexagon with a circle in it better represents the six delocalized pi electrons of the three double bonds ii. Cyclic conjugation in benzene leads to greater stabilization than other nonconjugated trienes II. Stability of Benzene a. Hydrogenation of benzene i. More difficult than normal hydrogenations ii. Can use either Rh or Pt as catalyst iii. Benzene consumes 3 molar equivalents of H to give cyclohexane iv. Resonance Energy- a measure of how much more stable benzene is than would be predicted on the basis of its formulation as a pair of rapidly interconverting 1,3,5-cyclohexatrienes. v. The resonance energy of benzene is large (6 to 10 x conjugated triene). Since the resonance enery is very large it and its related compounds are put in a group called aromatic
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III. Substituted Derivatives of Benzene and Nomenclature a. All compounds that contain a Benzene ring are aromatic. b. Nomenclature i. Monosubstituted Benzene- Attach the name of the substituent before benzene to name a monosubstituted benzene (bromobenzene, tert-butylbenzene, nitrobenzene ii. Dimethyl Derivatives of benzenes are called xylenes 1. Ortho (o)- 1,2-disubstituted benzene ring 2. Meta (m)- 1,3-disubstituted benzene ring 3. Para (p)- 1,4-disubstituted benzene ring iii. Trisubstituted benzene - 1. Use numbers to describe C on ring
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This note was uploaded on 06/29/2008 for the course CHM 2212 taught by Professor Mcquade during the Spring '08 term at FSU.

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Chapter 11 - Chapter 11 Arenes and Aromaticity I Benzenea...

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