20%20Ch14 - CHAPTER 14 Aromaticity Reactions of Benzene...

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407 CHAPTER 14 Aromaticity Reactions of Benzene Important Terms aliphatic compound an organic compound with a higher hydrogen-to-carbon ratio than an aromatic compound. annulene a monocyclic hydrocarbon with alternating double and single bonds. antiaromatic compound a cyclic and planar compound with an uninterrupted cloud of electrons containing an even number of pairs of π electrons. aromatic compound a cyclic and planar compound with an uninterrupted cloud of electrons containing an odd number of pairs of π electrons. benzyl group CH 2 Clemmensen reduction a reaction that reduces the carbonyl group of a ketone to a methylene group using Zn(Hg)/HCl, . electrophilic aromatic a reaction in which an electrophile substitutes for a hydrogen of an aromatic ring. substitution reaction Friedel-Crafts acylation an electrophilic substitution reaction that puts an acyl group on an aromatic ring. Friedel-Crafts alkylation an electrophilic substitution reaction that puts an alkyl group on an aromatic ring. Gatterman-Koch reaction a reaction that uses a high-pressure mixture of carbon monoxide and HCl to form benzaldehyde. halogenation reaction with a halogen (Br 2 , Cl 2 ). heteroatom an atom other than a carbon atom or a hydrogen atom. heterocyclic compound a cyclic compound in which one or more of the atoms of the ring are heteroatoms. (heterocycle) Hückel’s rule the number of π electrons in a cyclic uninterrupted π cloud that cyclic and planar or the 4 n + 2 rule compound must have in order to be aromatic. nitration substitution of a nitro group (NO 2 ) for a hydrogen of an aromatic ring. phenyl group C 6 H 5
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408 Chapter 14 principle of microscopic states that the mechanism for a reaction in the forward direction has the same reversibility intermediates and the same transition states as the mechanism for the reaction in the reverse direction. Stille reaction a reaction that will replace a bromine substituent on an aromatic ring with an alkyl substituent. sulfonation substitution of a hydrogen of an aromatic ring with a sulfonic acid group (SO 3 H). Suzuki reaction a reaction that will replace a bromine substituent on an aromatic ring with an alkyl substituent. Wolff-Kishner reduction a reaction that reduces the carbonyl group of a ketone to a methylene group using NH 2 NH 2 /HO - , .
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Chapter 14 409 Solutions to Problems 1. a. In the case of 9 pairs of π electrons, there are 18 electrons. Therefore, 4 n + 2 = 18 and n = 4. b. Because it has an odd number of pairs of π electrons, it will be aromatic if it is cyclic, planar, and if every atom in the ring has a p orbital. 2. a. Notice that each resonance contributor has a charge of –1. b. All five ring atoms share the negative charge. 3. a. + This is the only one that is aromatic; it is cyclic, planar every ring atom has a p orbital and it has one pair of π electrons.
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This note was uploaded on 03/29/2010 for the course CHE 118A 118a taught by Professor Kent during the Spring '10 term at UC Davis.

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20%20Ch14 - CHAPTER 14 Aromaticity Reactions of Benzene...

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