1. Benzene & Aromatic Compounds By: Dr. Shatha alaqeel

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. n = 0 (4x0)+2 = 2 π elect. not aromatic
n = (4x1)+2 = 6 π electrons aromatic
n = (4x2)+2 = 10 π elect. aromatic
n = (4x0)+2 = 2 π elect. not aromatic

8. Excercise
Apply Huckel,s rule to the following

9. Some Aromatic Ions

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

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

13. Nomenclature of Organic Compounds

15. -C6H5, Ph Φ
Phenyl group
Benzyl group

17. Disubstituted Benzene

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

19. 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

20. Some disubstituted benzenes have common names

21. Polysubstituted Benzene
Number so as to give the lowest possible numbering to the substituents

23. Electrophilic Aromatic Substitution Reactions

24. Summary of the electrophilic substitution reactions

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

26. 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

27. Orientation effects of substituents in electrophilic aromatic substitution reactions of monosubstituted Benzenes
Alkyl groups and groups with lone pairs direct new groups to ortho-, para-
positions and speed-up the reaction (activating groups).
Halogens direct new groups to ortho-, para- positions but it slow down the
reaction (deactivating).
Electron withdrawing groups such as nitro, nitrile, and carbonyl direct new
groups to the meta-position and slow the reaction down (deactivating).
Thus the order of reactivity of benzene and monosubstituted benzene derivatives as in the following
Substituted benzene with o,p directors > Benzene > Halobenzene derivatives > Substituted benzene with m- directors