1. DIRECTIVITY AND
RING ACTIVATION / DEACTIVATION

2. Nitration of Anisole ACTIVATED RING HNO3 H2SO4 anisole ortho para+
H2SO4
anisole
ortho
para
Reacts faster
than benzene
= “ACTIVATED”
The -OCH3 group when it preexists on the ring gives only
ortho and para products, and no meta.
Substituents that cause this result are called o,p directors
and they usually activate the ring.

3. Nitration of Methyl Benzoate
DEACTIVATED RING
Nitration of Methyl Benzoate
HNO3
H2SO4
meta
methyl benzoate
Reacts slower
than benzene
= “DEACTIVATED”
The -COOMe group when it preexists on the ring gives only
meta, and no ortho or para products.
Substituents that cause this result are called m directors
and they usually deactivate the ring.

4. SUBSTITUENT CATEGORIES
Most ring substituents fall into one of these two categories:
o,p - directors
m- directors
activate the ring
deactivate the ring
We will look at one of each kind in order to
understand the difference…..

5. NITRATION OF ANISOLE

6. Nitration of Anisole ortho meta para activated ring actual products+
para

7. :
ortho
EXTRA!
meta
para :
EXTRA!

8. Energy Profiles meta ortho para Ea ortho-para director
NITRATION OF ANISOLE
benzenium
intermediate
RECALL:
HAMMOND
POSTULATE Ea
meta
benzenium
intermediates
have more
resonance
ortho
para
ortho-para
director

9. X BENZENIUM IONS GIVE ELIMINATION INSTEAD OF ADDITION
ADDITION REACTION
doesn’t happen
resonance would be lost X
ELIMINATION REACTION
restores aromatic ring
resonance
( 36 Kcal / mole )

10. NITRATION OF METHYL BENZOATE

11. Nitration of Methyl Benzoate
ortho
meta
para
deactivated
ring
actual
product
meta

12. d- d+
BAD!
ortho
meta d- d+
para
BAD!

13. Energy Profiles ortho para meta meta director
NITRATION OF METHYL BENZOATE
some
benzenium
resonance
structures
have a bad
situation
ortho
para
meta
meta
director

14. DIRECTIVITY OF SINGLE GROUPS

15. ortho, para - Directing Groups
Groups that donate
electron density
to the ring.
PROFILE: : E+
increased
reactivity
+I Substituent
+R Substituent ..
These groups also
“activate” the ring, or
make it more reactive.
CH3-O-
CH3- .. .. R-
CH3-N- ..
-NH2 ..
The +R groups activate
the ring more strongly
than +I groups.
-O-H ..

16. meta - Directing Groups
Groups that withdraw
electron density from
the ring.
PROFILE: d+ d- E+
decreased
reactivity
-I Substituent
-R Substituent
These groups also
“deactivate” the ring,
or make it less reactive. + + -
-SO3H

17. Halides - o,p Directors / Deactivating
THE EXCEPTION
Halides - o,p Directors / Deactivating
Halides represent a special case: .. : :
They are o,p directing groups
that are deactivating E+
They are o,p directors (+R effect )
They are deactivating ( -I effect )
Most other other substituents fall
into one of these four categories:
+R / -I / o,p / deactivating
1) +R / o,p / activating -F
-Cl
-Br -I
2) +I / o,p / activating
3) -R / m / deactivating
4) -I / m / deactivating

18. PREDICT !
o,p m
o,p m

19. DIRECTIVITY OF MULTIPLE GROUPS

20. GROUPS ACTING IN CONCERT
steric
crowding
o,p director
m-director
very
little
formed
HNO3
H2SO4
When groups direct to the
same positions it is easy to
predict the product.
major
product

21. GROUPS COMPETING X o,p-directing groups win over m-directing groups
too
crowded X
HNO3 +
H2SO4

22. RESONANCE VERSUS INDUCTIVE EFFECT
HNO3
H2SO4
major
product +I
resonance effects are more
important than inductive effects

23. SOME GENERAL RULES 1) Activating (o,p) groups (+R, +I) win over
deactivating (m) groups (-R,-I).
2) Resonance groups (+R) win over inductive (+I) groups.
3) 1,2,3-Trisubstituted products rarely form due to
excessive steric crowding.
4) With bulky directing groups, there will usually be more
p-substitution than o-substitution.
5) The incoming group replaces a hydrogen, it will not
usually displace a substituent already in place.

24. HOW CAN YOU MAKE ...
only,
no para

25. BROMINE - WATER REAGENT
PHENOLS AND ANILINES

26. BROMINE IN WATER .. .. .. .. .. .. - : : : : : .. .. .. .. .. .. : ..
This reagent works only with highly-activated rings
such as phenols, anisoles and anilines. .. .. .. .. .. .. - : : : : : .. .. .. .. + .. .. : + .. +
bromonium
ion
etc

27. PHENOLS AND ANILINES REACT
Br2
H2O
All available
positions are
bromiated.
Br2
H2O

28. AROMATICITY
THE HUCKEL RULE

29. AROMATICITY QUESTION:
Are all fully-conjugated, cyclic systems aromatic?
36 kcal/mole RE ? ? ?
KNOWN
AROMATIC ? ?
Do these other rings have the
same kind of stability as benzene?

30. .. HUCKEL 4n+2 RULE AROMATICITY
Prediction: Compounds that have 4n+2 pi electrons in
a cyclic array will be aromatic.
4n+2 series = 2, 6, 10, 14, 18, 22, 26, 30 …….. etc.
The rule was derived by observation of
POLYCYCLIC AROMATIC COMPOUNDS 6 10 14
benzene
naphthalene
anthracene 14 18

31. Aromatic Compounds Have Special Properties
1) Must be cyclic and fully conjugated
2) Must have 4n+2 p electrons in the system
3) Must have the entire system planar
4) Will have no unpaired electrons in
the p system molecular orbitals
planar
system
Characteristic Properties:
1) Special chemical stability
2) Give substitution reactions instead of addition
3) Show a ring currrent in the NMR
(Chapter 13, Section 13.8)

32. Ring Current in Benzene
Circulating p electrons
Deshielded H H
A proton placed in the
middle of the ring would
be shielded! Bo
Secondary magnetic field
generated by circulating p
electrons deshields aromatic
protons

33. RING CURRENTS CAN BE SEEN IN THE NMR
AROMATIC - SHOWS
A RING CURRENT
-1.0 ppm
2.0 ppm
18 p
inner hydrogens ppm
outer hydrogens ppm
-1.4 ppm

34. HUCKEL MNEMONIC CYCLIC p MOLECULAR ORBITAL ARRAYS 1) Draw a circle
2) Inscribe the ring in the circle point down
3) Each point where the polygon (ring)
touches the circle represents an
energy level.
4) Place the correct number of electrons in
the orbitals, starting with the lowest
energy orbital first. E N R G Y

35. BENZENE p M.O. levels Aromatic compounds will have all of the occupied
completely
filled with no
unpaired
electrons.
6p electrons
AROMATIC E N R G Y
closed*
shell
(*completed
level)

36. CYCLOBUTADIENE . . ANTI-AROMATIC Does not have a completed
shell and has unpaired electrons.
4p electrons
Does not have 4n+2 p electrons. E N R G Y
open*
shell . .
(*incomplete
level)
DIRADICAL

37. CYCLOOCTATETRAENE ANTI-AROMATIC 8p electrons Does not have a completed
shell and has unpaired electrons.
Does not have 4n+2 p electrons. E N R G Y
open*
shell
not planar
(*incomplete
level)

38. SOME CYCLIC POLYENES 10 p = 4(2) + 2 16 p 12 p 18 p = 4(4) + 2
ANNULENES
10 p = 4(2) + 2
16 p
BUT CANNOT BE PLANAR
(see the hydrogens)
[10]-annulene
[16]-annulene
12 p
18 p = 4(4) + 2
AROMATIC
[12]-annulene
[18]-annulene
[20]-annulene
14 p = 4(3) + 2
20 p
AROMATIC
[14]-annulene

39. HETEROCYCLIC COMPOUNDS
The unshared pairs are in the
cyclic pi system (one pair in each case). .. .. .. .. .. ..
pair not in
p system
pyridine
pyrrole
furan
thiophene
All have 6p electrons in a cyclic array.
These compounds have reactions similar to benzene,
rather than to alkenes. They will give substitution reactions
under conditions similar to those for benzene.

40. X CYCLOPENTADIENYL ANION AND CATION .. - - Cl The methylene
hydrogens are
acidic.
This compound
does not dissolve
in water.
NaOEt
EtOH X 6p 4p ..
AROMATIC -
ANTI-AROMATIC + - Cl
The cation does not
form at all.
The anion forms readily.

41. X CYCLOHEPTATRIENYL ANION AND CATION - .. - Cl This compound
ionizes easily in
water.
The methylene
hydrogens are
not acidic. X
NaOEt
EtOH 8p 6p .. + -
ANTI-AROMATIC
AROMATIC - Cl
Doesn’t form
easily.
Dissolves in water.