1. Case Western Reserve University
Chapter 15
Aromaticity
Reactions of Benzene
Organic Chemistry
4th Edition
Paula Yurkanis Bruice
Irene Lee
Case Western Reserve University
Cleveland, OH
©2004, Prentice Hall

2. Criteria for Aromaticity
1. A compound must have uninterrupted cyclic cloud of
p electrons above and below the plane of the molecule
2. The p cloud must contain an odd number of pairs
of p electrons

3. Hückel’s Rule For a planar, cyclic compound to be aromatic, its
uninterrupted p cloud must contain (4n + 2) p electrons,
where n is any whole number

4. Monocyclic hydrocarbons with alternating single and
double bonds are called annulenes
Cyclobutadiene is not aromatic because it has an even
number of electron pairs
Cyclooctatetraene is not aromatic because it is
nonplanar

5. Neither cyclopropene nor the cyclopropenyl anion is
aromatic
The cyclopropene
cation is aromatic

6. sp3
sp3
cycloheptatriene
cyclopentadiene
2 pairs of p electrons
not aromatic
interrupted p cloud
not aromatic

7. These compounds are aromatic

8. Aromatic Heterocyclic Compounds
A heterocyclic compound is a cyclic compound in which
one or more of the ring atoms is an atom other than
carbon

9. Pyridine Is Aromatic

10. Pyrrole Is Aromatic

11. Furan Is Aromatic

12. Examples of Heterocyclic
Aromatic Compounds

13. The Effect of Aromaticity on the pKa Values of Some Compounds

15. Aromaticity influences chemical reactivity

16. A compound is antiaromatic if it is a planar, cyclic
compound with an uninterrupted ring of p cloud,
but it contains even number of pairs of p electrons

17. A Molecular Orbital Description of Aromaticity and Antiaromaticity

18. Benzene is a nucleophile that reacts with an electrophile

19. Reaction Coordinate Diagrams for the Two Benzene Reactions

20. General Mechanism for Electrophilic Aromatic Substitution of Benzene
slow
fast B:

21. Halogenation of Benzene

24. Nitration of Benzene

25. Sulfonation of Benzene

28. Friedel–Crafts acylation must be carried out with more
than one equivalent of AlCl3

30. The carbocation will rearrange to a more stable species

33. alkylation of benzene by an alkene

34. It is not possible to obtain a good yield of an alkylbenzene containing a straight-chain group via Friedel–Crafts alkylation

35. However, a Friedel–Crafts acylation–reduction works well
This method avoids using a large excess of benzene in the reaction

36. Methodologies Used for
the Reduction Step

37. One needs to consider an alternative if there is another
functional group present in the compound