1. Benzene & Aromatic Compounds

2. Structure = Cyclic planner
Introduction
Name= Benzene
Chemical formula= C6H6
Structure = Cyclic planner
Hybridization= SP2
Bond angles= 120o
Bond Length= 1.39 A

3. 1) Benzene can be written as a six- membered ring with alternating single and doublebonds (Kekulé structure).
2) Benzene reacts with substitution reactions not with addition reactions

5. The Aromatic Character
When to say this compound is aromatic?
1) If it I cyclic
2) If it has π and σ alternating bonds
3) If it is planar

6. 4) Reacts with substitution not addition reactions 5) Contain (4n+2) π electrons This is called Huckel’s Rule Where n= 0,1,2,3,……. When n=0 π=2 n=1 π=6 n= 2 π=10 n= 3 π=14

7. Examples of aromatic compounds
Examples of non aromatic compounds

8. Excercise
Apply Huckel,s rule to the following

9. Not aromatic (does not follow Huckel,s rule
Not aromatic (not planar)

10. Stability of Benzene Benzene is more stable than cyclohexatriene
by 36 kcal\mol : Resonance energy

11. Nomenclature of Aromatic Compounds
1. Monosubstituted Benzenes
a. IUPAC name

12. b. Common Names Of Monosubstituted Benzenes

13. -C6H5, Ph Φ
Phenyl group
Benzyl group

15. Disubstituted Benzene
All disubstituted benzenes (two groups are attached to benzene), can give
rise to three possible positional isomers.

16. 2) When the substituents are different, they are arranged alphabetically

17. If one of the substituents is part of a common named compound, then the disubstituted benzene is named as a derivative of the parent compound

18. Some disubstituted benzenes have common names

19. Electrophilic Aromatic Substitution Reactions

20. Summary of the electrophilic substitution reactions

21. Side-Chain Reactions of Aromatic Compounds
a. Halogenation of an Alkyl Side Chain
b. Oxidation of an Alkyl Side Chain

22. Orientation effects of substituents in electrophilic aromatic substitution reactions of monosubstituted Benzenes
Meta directors
Ortho , para directors
-NO2
-SO3H
-COOH, -COOR
-CHO, -COR
-CN
-OH, -OR
-NH2, -NHR, -NR2
-C6H5
-CH3, -R (alkyl)
-F, -Cl, -Br, -I

23. Orientation effects of substituents in electrophilic aromatic substitution reactions of monosubstituted Benzenes
Alkyl groups and groups with lone pairs (electron donating groups) direct new groups to ortho-, para-positions and speed-up the reaction (i.e. o & p directors and activating groups).
Halogens direct new groups to ortho-, para- positions but they slow down the
reaction (i.e. halogens are o & p directors and deactivating groups).
Electron withdrawing groups such as nitro, nitrile, and carbonyl direct new
groups to the meta-position and slow the reaction down (i.e. i.e. m directors and deactivating groups).