Figure: 14-01-01UN Title: Hydrogenation of cyclohexene and benzene. Caption: The DHº for the hydrogenation of benzene is predicted to be -85.8 kcal/mole.

Figure: 14-01-02UN Title: The DHº for the hydrogenation of benzene was found experimentally to be -49.8 kcal/mole. Caption: This number is much less than calculated.

Figure: 14.1 Title: Figure 14.1. Structure, electron cloud, and electrostatic potential maps of benzene. Caption: (a) Every carbon of benzene has a p orbital. (b) The overlap of the p orbitals forms a cloud of pi electrons above and below the plane of the atoms. (c) The electrostatic potential map for benzene shows that all the carbon-carbon bonds have the same electron density.

Figure: 14.2 Title: Figure 14.2. The difference between the energy levels of "cyclohexatriene" + hydrogen versus cyclohexane, and the difference in the energy levels of benzene + hydrogen versus cyclohexane. Caption: Benzene is more stable.

Figure: 14-02-01UN Title: Cyclobutadiene, benzene, and cyclooctatetraene are examples of annulenes. Caption: Monocyclic compounds with alternating single and double bonds are called annulenes.

Figure: 14-02-02UN Title: Cyclopentadiene, cyclopentadienyl cation, and cyclopentadienyl anion. Caption: Cyclopentadiene and the cyclopentadienyl cation are not aromatic. The cyclopentadienyl anion is aromatic.

Figure: 14-02-03UN Title: Resonance contributors and resonance hybrid for cyclopentadienyl anion. Caption: All carbons are equivalent in the cyclopentadienyl anion.

Figure: 14-02-04UN Title: Naphthalene, phenanthrene, and chrysene. Caption: Naphthalene, phenanthrene, and chrysene are aromatic.

Figure: 14-02-15UN Title: Pyridine, pyrrole, furan, and thiophene. Caption: Pyridine, pyrrole, furan, and thiophene are heterocyclic aromatic compounds.

Figure: 14-02-17UN Title: Orbital structure of pyridine. Caption: A pyridine molecule showing p atomic orbitals on the nitrogen and carbon atoms.

Figure: 14-02-18UN Title: Resonance structures of pyrrole. Caption: The lone pair electrons are in a p orbital that overlaps the p orbital of the adjacent carbons, forming a pi bond.

Figure: 14-02-19UN Title: Orbital structures of pyrrole and furan. Caption: Schematic of pyrrole and furan molecules showing p atomic orbitals on the ring.

Figure: 14-02-20UN Title: Resonance contributors of furan. Caption: The oxygen is sp2 hybridized. One lone pair is in an sp2 orbital. One lone pair is in a p orbital that overlaps the p orbitals of adjacent carbons forming a pi bond.

Figure: 14-02-21UN Title: Quinoline, indole, imidazole, purine, and pyrimidine. Caption: Quinoline, indole, imidazole, purine, and pyrimidine are heterocyclic aromatic compounds.

Figure: 14-02-22UN Title: The pKa values of cyclopentadiene and ethane. Caption: Cyclopentadiene has a lower pKa value because of delocalization of the electrons.

Figure: 14-02-23UN Title: Cycloheptatrienyl bromide—covalent and ionic. Caption: Cycloheptatrienyl bromide acts like an ionic compound; it is soluble in water.

Figure: 11 Title: Problem 11 -- solved. Draw the arrows going from one resonance contributor to the next in the cycloheptatrienyl cation. Caption: Draw the arrows from a double bond to the adjacent carbon-carbon bond, next to the positive charge.

Figure: 11 Title: Problem 11 -- solved. How many ring atoms share the positive charge in the cycloheptatrienyl cation? Caption: All seven atoms share the positive charge.

Figure: 14-02-25PSS1 Title: Identify the compound with the greatest dipole moment, I. Caption: Determine which compound has the greatest charge separation.

Figure: 14-02-26PSS2 Title: Identify the compound with the greatest dipole moment, II. Caption: The compound with the greatest charge separation is on the left.

Figure: 14-02-28 Title: Relative stabilities of aromatic, nonaromatic, and antiaromatic compounds. Caption: Antiaromatic compounds have even numbers of electron pairs in planar ring systems.

Figure: 14-02-29UN Title: Cyclobutadiene and cyclopentadienyl cation. Caption: Cyclobutadiene and cyclopentadienyl cation are both antiaromatic.

Figure: 14.3 Title: Figure 14.3. The distribution of electrons in the p molecular orbitals of (a) benzene, (b) the cyclopentadienyl anion, (c) the cyclopentadienyl cation, and (d) cyclobutadiene. Caption: The relative energies of the pi molecular orbitals in a cyclic compound correspond to the relative levels of the vertices.

Figure: 14-03-01UN Title: Nomenclature of monosubstituted benzenes, I. Caption: Bromobenzene, chlorobenzene, nitrobenzene, and ethylbenzene are named by attaching "benzene" after the name of the substituent.

Figure: 14-03-02UN Title: Nomenclature of monosubstituted benzenes, II. Caption: Toluene, phenol, aniline, and benzenesulfonic acid have names that incorporate the substituent.

Figure: 14-03-03UN Title: Nomenclature of monosubstituted benzenes, III. Caption: Anisole, styrene, benzaldehyde, benzoic acid, and benzonitrile have names that incorporate the substituent.

Figure: 14-03-04UN Title: Alkylbenzenes. Caption: Benzene rings with alkyl substituents are named as alkyl-substituted benzenes or phenyl-substituted alkanes.

Figure: 14-03-05UN Title: A phenyl group and a benzyl group. Caption: When a benzene ring is a substituent, it is called a phenyl group. A benzene ring with a methylene group is called a benzyl group.

Figure: 14-03-07UN Title: Electrophilic aromatic substitution. Caption: Benzene undergoes electrophilic aromatic substitution.

Figure: 14-03-08UN Title: The pi bond in a benzene ring attacks the electrophile to form a carbocation intermediate. Caption: The cloud of pi electrons is the nucleophile.

Figure: 14-03-09UN Title: The first step in an electrophilic addition reaction of an alkene. Caption: The first step in an electrophilic aromatic substitution reaction is very similiar to the first step in an electrophilic addition reaction of an alkene.

Figure: 14.4 Title: Figure 14.4. Reaction of benzene with an electrophile. Caption: Because the aromatic product is more stable, the reaction proceeds as (b) an electrophilic substitution reaction rather than (a) an electrophilic addition reaction.

Figure: 14.5 Title: Figure 14.5. Reaction coordinate diagrams for electrophilic aromatic addition and electrophilic aromatic substitution. Caption: Electrophilic aromatic addition yields products which are less stable than reactants because aromaticity is lost, whereas electrophilic aromatic substitution preserves aromaticity and yields products having stabilities comparable to those of reactants.

Figure: 14-05-01UN Title: An electrophilic aromatic substitution reaction. Caption: In an electrophilic aromatic substitution reaction, an electrophile becomes attached to a ring carbon and an H+ comes off the same carbon.

Figure: 14-05-02UN Title: General mechanism for electrophilic aromatic substitution. Caption: Benzene reacts with an electrophile forming a carbocation intermediate. A base abstracts a proton from the carbocation intermediate. The aromatic ring is regenerated.

Figure: 14-05-03UN Title: Bromination of benzene yields bromobenzene. Caption: A Lewis acid catalyst is required in this reaction.

Figure: 14-05-04UN Title: Chlorination of benzene yields chlorobenzene. Caption: The chlorination of benzene requires a Lewis acid catalyst.

Figure: 14-05-05UN Title: The reaction of bromine with ferric bromide yields a better electrophile in the bromination of benzene. Caption: The Br-Br bond is weakened.

Figure: 14-05-06UN Title: Mechanism for the bromination of benzene. Caption: The electrophile attaches to the benzene ring. A base removes a proton from the carbocation intermediate. The benzene ring is regenerated.

Figure: 14-05-07UN Title: The ferric bromide catalyst is regenerated. Caption: The ferric bromide can react with another bromine to form the intermediate.

Figure: 14-05-08UN Title: Mechanism for the chlorination of benzene to form chlorobenzene. Caption: The electrophile attaches to the ring. A base removes a proton from the carbocation intermediate. The benzene ring is regenerated.

Figure: 14-05-10UN Title: Iodination of benzene yields iodobenzene. Caption: Electrophilic iodine (I+) is obtained by treating iodine with an oxidizing agent such as nitric acid.

Figure: 14-05-11UN Title: Mechanism for the iodination of benzene to yield iodobenzene. Caption: The electrophile attaches to the benzene ring. A base removes a proton from the carbocation intermediate. The benzene ring is regenerated.

Figure: 14-05-13UN Title: Nitration of benzene yields nitrobenzene. Caption: The nitration of benzene with nitric acid requires sulfuric acid as a catalyst.

Figure: 14-05-14UN Title: Nitric acid and nitronium ion. Caption: The nitronium ion is the electrophile in the nitration of benzene.

Figure: 14-05-15UN Title: Mechanism for the formation of the nitronium ion. Caption: The nitronium ion is made from nitric acid and sulfuric acid.

Figure: 14-05-16UN Title: Mechanism for the nitration of benzene to make nitrobenzene. Caption: The electrophile attaches to the ring. The base removes the proton from the carbocation intermediate. The benzene ring is regenerated.

Figure: 21 Title: Problem 21 -- solved. Propose a mechanism, II. Caption: The electrophile is D+. The D+ attaches to the ring carbon and H+ comes off.

Figure: 14-06-01UN Title: An acyl group and an alkyl group. Caption: Friedel-Crafts acylation places an acyl group on the ring. Friedel-Crafts alkylation places an alkyl group on the ring.

Figure: 14-06-04UN Title: The Friedel-Crafts acylation of benzene yields a ketone. Caption: An acyl chloride or an anhydride can be used for Friedel-Crafts acylation.

Figure: 14-06-05.1UN Title: Mechanism for the Friedel-Crafts acylation of benzene to yield a ketone. Caption: The electrophile attaches to the ring. The base removes the proton from the carbocation intermediate. The benzene ring is regenerated.

Figure: 14-06-05UN Title: Formation of the acylium ion. Caption: The acylium ion is formed from an acyl halide and aluminum chloride.

Figure: 14-06-06UN Title: Complex formation of a ketone with aluminum chloride. Caption: A Friedel-Crafts acylation must be carried out with excess aluminum chloride, since the aluminum chloride can complex with the ketone.

Figure: 14-06-09UN Title: The Friedel-Crafts alkylation of benzene produces an alkylbenzene. Caption: The Friedel-Crafts alkylation substitutes an alkyl group for a hydrogen.

Figure: 14-06-10.1UN Title: Mechanism for the Friedel-Crafts alkylation of benzene to yield a ketone. Caption: The electrophile attaches to the ring. The base removes the proton from the carbocation intermediate. The benzene ring is regenerated.

Figure: 14-06-10UN Title: Formation of a carbocation in a Friedel-Crafts alkylation. Caption: The carbocation is formed from the reaction of an alkyl halide with aluminum chloride.

Figure: 14-06-11UN Title: Friedel-Crafts alkylation of benzene with 1-chlorobutane will give primarily 2-phenylbutane. Caption: The primary butyl group undergoes a 1,2-hydride shift to yield a secondary butyl group.

Figure: 14-06-12UN Title: The Friedel-Crafts alkylation of benzene with 1-chloro-2,2-dimethylpropane gives 2-methyl-2-phenylbutane. Caption: The primary carbocation will undergo a 1,2-methyl shift to form a tertiary carbocation.

Figure: 14-06-13UN Title: Rearrangement of a primary carbocation to yield a tertiary carbocation. Caption: The primary carbocation undergoes a 1,2-methyl shift to yield a tertiary carbocation.

Figure: 14-06-14UN Title: Benzene is alkylated with 2-butene to give sec-butylbenzene. Caption: Benzene can react with carbocations generated from the reaction of an alkene with an acid.

Figure: 14-06-15UN Title: Benzene reacts with 2-propanol to form isopropylbenzene. Caption: Benzene can react with carbocations generated from the reaction of an alcohol with an acid.

Figure: 14-06-17UN Title: Friedel-Crafts alkylation of benzene with 1-chlorobutane yields primary sec-butylbenzene. Caption: The primary butyl carbocation rearranges to form a secondary butyl carbocation.

Figure: 14-06-18UN Title: Friedel-Crafts acylation of benzene with propanoyl chloride yields propyl phenyl ketone, which is reduced to butylbenzene. Caption: A straight-chain alkyl group can be placed on a benzene ring by means of a Friedel-Crafts acylation reaction, followed by reduction of the carbonyl group to a methylene group.

Figure: 14-06-19UN Title: Clemmenson reduction and Wolff-Kishner reduction of ethyl phenyl ketone to propylbenzene. Caption: The Clemmenson reduction uses an acidic solution of zinc dissolved in mercury. The Wolff-Kishner reduction uses hydrazine under basic conditions.

Figure: 14-06-27 Title: Reaction of propylbenzene with NBS yields 1-bromo-1-phenylpropane. Caption: N-Bromosuccinimide will selectively brominate at the benzylic carbon.

Figure: 14-06-29UN Title: 1-Bromo-1-phenylethane can undergo an elimination reaction to yield styrene. Caption: Halosubstituted alkyl groups can undergo E1 and E2 reactions to yield alkenes.

Figure: 14-06-30UN Title: Catalytic hydrogenation of styrene gives ethylbenzene. Caption: Addition of hydrogen to a double bond is an example of a reduction reaction.

Figure: 14-06-31UN Title: Hydrogenation of benzonitrile gives benzylamine. Caption: Addition of hydrogen to a triple bond is an example of a reduction reaction.