This document provides an overview of aromatic electrophilic substitution reactions (AES). It defines important terms like arenium ions, electrophiles, nucleophiles and discusses the effects of substituents on reactivity. The mechanisms of common AES reactions like nitration, sulfonation, Friedel-Crafts alkylation and acylation are covered. The document also discusses topics like the mesomeric and inductive effects of substituents, the synthesis of tribromobenzene, and the relative reactivities of benzene and substituted benzenes in bromination. Examples of AES on phenols, xylenes, cresols and other aromatic compounds are provided.

1. Dr. Vajiravelu Sivamurugan
Professor in Chemistry
Pachaiyappa’s College
E mail: sivamu1177@gmail.com
+91-9444316582

3. What is
arenium
ion?
Electrophile
s (E+)
Nucleophile
s (Nu-)
Ortho/para
directing
groups
Meta
directing
groups
Inductive
effect (+I/-I)
Mesomeric
effect (+M/-
M)
BASICS

5. GENERAL MECHANISM FOR AROMATIC ELECTROPHILIC
SUBSTITUTION

8. OVERVIEW OF AES (SARE
2)
Nitration
Sulphonation
Friedel-Crafts Alkylation
Friedel-Crafts Acylation
Halogenation

9. MESOMERIC EFFECT
• The mesomeric effect in chemistry is a property of substituents or functional groups in a
chemical compound.
• The effect is used in a qualitative way and describes the electron withdrawing or releasing
properties of substituents based on relevant resonance structures and is symbolized by the
letter M.
• The mesomeric effect is negative (–M) when the substituent is an electron-withdrawing
group and the effect is positive (+M) when the substituent is an electron releasing group.
• +M EFFECT ORDER :
–O− > –NH2 > –NHR > –OR > –NHCOR > –OCOR > –Ph > –F > –Cl > –Br > –I
• -M EFFECT ORDER :
–NO2 > –CN > --S(=O)2−OH > –CHO > –C=O > –COOCOR > –COOR > –COOH > –CONH2 >
–COO−

10. INDUCTIVE EFFECT
• The inductive effect is an experimentally observed effect of the transmission of
charge through a chain of atoms in a molecule, giving rise to a permanent dipole
in a bond.
• It is present in a σ bond as opposed to electromeric effect which is present on a
π bond.
• All halides are electron withdrawing groups, and all alkyl are electron donating.
• If the electronegative atom is then joined to a chain of atoms, usually carbon, the
positive charge is relayed to the other atoms in the chain. This is the electron-
withdrawing inductive effect, also known as the
• However, some groups, such as the alkyl group, are less electron-withdrawing
than hydrogen and are therefore considered as electron-releasing. This is
electron-releasing character and is indicated by the

11. SYNTHESIS OF 1,3,5-TRIBROMO BENZENE

12. CH3
CON HNO3
CON H2SO4
CH3
NH2
NH4OH
Zn
CH3
NH2OH
CH3
NH2
BAMBERGER
REARRANGEMENT
ACID MEDIUM
OH
NO2

13. Con HNO3
Con H2SO4
O OH
Br
O2N

16. ELECTROPHILIC SUBSTITUTION ON PHENOLS
No catalyst involved unlike benzene
need Lewis acid catalyst

18. SYNTHESIS OF PARACETAMOL AND ASPIRIN
Kolbe–Schmitt process Phenoxide is more reactive than phenol

19. RELATIVE REACTIVITY RATES OF BROMINATION

20. ELECTROPHILIC SUBSTITUTION ON XYLENES

21. ELECTROPHILIC SUBSTITUTION ON CRESOLS
OH
CH3
OH
CH3
OH
CH3
E+
E+
E+
E+ E+E+
o-CRESOL m-CRESOL p-CRESOL

22. ELECTROPHILIC SUBSTITUTION ON PHENOLS
OH
OH
OH
OH
OH
OH
E+
E+
E+
E+ E+E+
RESORCINOLCATECHOL HYDROQUINONE

23. MAKING AROMATIC AMINES LESS REACTIVE
Amine is more reactive

24. ALKYL BENZENES ALSO REACT AT THE ORTHO AND PARA POSITIONS
Aromatic proton chemical shfft (ppm) in 1H NMR
Electron donating nature increases
Electron density increases
Chemical shift decreases

25. AES ON BENZENE CONTAINING EWG

26. 1H NMR CHEMICAL SHIFT

27. HALOGENS SHOW EVIDENCE OF BOTH ELECTRON WITHDRAWAL
AND DONATION
1. All the halobenzenes react more slowly
than benzene itself.
2. Halogens are ortho, para directing

29. TWO OR MORE SUBSTITUENTS MAY COOPERATE OR COMPETE

30. Bromination of methyl benzamide goes ortho to the –NHCOMe group but meta
to the methyl group

31. WHAT PRODUCT WILL BE FORMED?

32. AES ON AROMATIC HETEROCYCLIC COMPOUNDS

33. Pyridine is bad at electrophilic aromatic substitution

34. ACTIVATED PYRIDINES WILL DO ELECTROPHILIC AROMATIC
SUBSTITUTION

35. PYRIDINE-N-OXIDE

36. PYRROLE

37. WHY 2-ND POSITION IS PREFERRED OVER 3-RD POSITION?

38. FURAN AND THIOPHENE

40. GATTERMANN–KOCH REACTION

41. FORMATION OF ACYLIUM ION

43. VILSMEIER-HAACK REACTION

44. FORMATION OF CHLOROIMINIUM SALT

46. ACKNOWLEDGEMENT
Chapter 21 : Aromatic electrophilic substitution