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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5574_Библиотеки_им_академика_М_И_Перельмана.pdf
Unstable charge on carbon-carrying substituent
(I)
Para attac
k
⊕
NO
2
HNO
2
(III)
NO
2
HNO
2
⊕
(II)
NO
2
⊕
H
NO
2
(V)
⊕
H
NO
2
⊕
(VI)
H
NO
2
Ortho attack
⊕
NO
2
NO
2
NO
2
H
NO
2
(IV)
⊕
(IX)
H
NO
2
Meta attack
⊕
NO
2
NO
2
(VII)
H
NO
2
⊕
NO
2
(VIII)
H
NO
2
351
2
2. electron release through resonance
a. Ortho and para directing groups having –I and +M effects (carbonium ions formed by attack
at para, ortho and meta positions of aniline):
due to the electronegativity of the
2,
The effects of 2 and
positive charge.
2 group of aniline is
352
Ortho attack
Para attack
(IV)
Stable
H
Y
⊕
NH
2
H
Y
(I)
⊕
:NH
2
H
Y
(II)
⊕:NH
2
⊕
:NH
2
H
Y
(III)
H
Y
⊕:NH
2
(VIII)
:NH
2
(VI)
⊕
H
Y
⊕
:NH
2
(VII)
H
Y
Stable
⊕
:NH
2
H
Y
(V)
⊕
: NH
2
(XI)
H
Y
⊕
: NH
2
(IX)
H
Y
⊕
: NH
2
(X)
H
Y
hydrogen) has a complete octet of electrons.
2
and para positions to 2 groups.
2 and
Effect of halogens (carbonium ions formed by attack at para, ortho and meta positions of
chlorobenzene
Stable
⊕
:Cl:
:
H
Y
(I)
:Cl:
:
⊕
H
Y
(II)
(IV)
Para attack
H
Y
:Cl:
:
⊕
:Cl:
:
(III)
H
Y
⊕
⊕
:Cl:
:
(VI)
⊕
H
Y
:Cl:
:
⊕
(VII)
H
Y
:Cl:
:
H
Y
⊕
(VIII)
Ortho attac
k
Meta attack
:Cl:
:
⊕
H
Y
(V)
:Cl:
:
⊕
H
Y
(IX) (X) (XI)
:Cl:
:
:Cl:
:
⊕
⊕
H
Y
H
Y
353
chlorine and other halogens.
354
Table 9.1 orientation and reactivity effect of ring substituents
activating substituents
ortho & para-orientation
6H5
3
2
2
R
6H
5
3
deactivating substituents
meta-orientation
3
PR
3
SR
2
3H
2R
2
(+)
(+)
(+)
2H
2R
deactivating substituents
ortho & para-orientation
F
2
Br
2
2
REVISION QUESTIONS
dition reactions.
(c) phlorotoluene from toluene
(d) p
(e) Benzyl alcohol from toluene
MULTIPLE CHOICE QUESTIONS
(a) sp sp3
(c) sp2
catalyst.
355
(a)
S
(c) S
(d)
3
3
33
356
CH
3
C
+
O
(a) m
(c) o
3
o
m
22 gives
(a) o
(c) op
2 3 catalyst
(a)
(c) There is delocalization of electrons
3 catalyst
(c) Platinum catalyst (d) Al23 catalyst
3 is to
(a) Form a
23 catalyst
3 is used to generate
+
2
(c) Benzal chloride (d) Benzophenone
2
(c) n
357
(a) 2
(c) 3 (d)
(c) Acetanide (d) Benzaldehyde
(a) Donates electrons that increase electron density at ortho and para positions favouring
Donates electrons that increase electron density at ortho and para positions favouring
(c) D
(d) D
358
(a) S Faster rate
(c) S annot predict
p3 gives
(a) m
(c) p
ANSWERS
1. (c) 2. 3. (d) (a) 5. 6. (a) 8. (d) (c)
11. (a) 12. (d) 13. (a) 15. 16. (c) 18. (d)
(a) 21. 22. (c) 23. 25. 26. (c)
Aliphatic
Aromatic
C
2H5
aRENES
5
10
10.1 Introduction, 10.2 Structure and Nomenclature of Arenes, 10.2.1 Nomenclature, 10.3 Isomerism in Arenes, 10.4 The Aromatic
Character, 10.4.1 Huckel Rule, 10.4.2 Aromatic, Antiaromatic and Nonaromatic Compounds, 10.5 Preparation of Arenes, 10.6 Physical
Properties, 10.7 Chemical Properties, 10.8 Ortho–Para Ratio in the Formation of Disubsitution Derivatives, 10.9 Orientation in Disubstituted
Benzene (Introduction of a Third Group in Benzene Ring), 10.10 Some Individual Members, 10.10.1 Toluene, Methylbenzene, Phenylmethane
(C
), 10.10.2 Styrene (an Alkenyl Benzene), 2-Phenyl Ethane, Phenylethylene, Vinylbenzene, 10.10.3 Xylene, Dimethylbenzene
6H5CH3
10.1 INTRODUCTION
The benzenoid hydrocarbons, which contain both aliphatic and aromatic units, are called arenes (meaning
fragrant odour, i.e. sweet smell). Some examples of arenes are toluene (C
xylene (C
The aliphatic part may consist of alkyl or alkenyl or alkynyl side chain
attached to the benzene nucleus. Thus, we may have alkyl benzenes (e.g.
toluene, xylene) alkenyl benzenes (e.g. styrene, allyl benzene) and alkynyl
benzene (e.g. phenyl acetylene).
The chemistry of arenes will thus be due to both the aromatic part (benzene
part) and the aliphatic part (alkane, alkene or alkyne part) and each part will inuence the chemistry of the
other to some extent.
(CH3)2) and mesitylene (C6H3(CH3)3).
6H4
(C
6H4
Throughout his life Newton must have de-
voted at least as much attention to chemistry
and theology as to mathematics.
–W.W.R. Ball
Chapter Outline
(CH3)2), 10.10.4 Mesitylene, 1,3,5-Trimethylbenzene (C6H2(CH3)3)
),
6H5CH3
10.2 STRUCTURE AND NOMENCLATURE OF ARENES
Arenes may be classied as monoalkylbenzenes, alkenylbenzenes and alkynylbenzenes depending upon the
nature of aliphatic part.
Structure
Aromatic hydrocarbons obtained by replacement of one or more hydrogen atoms of the benzene ring by
hydrocarbon substituents such as alkyl, alkenyl or aryl groups are called arenes.
360
PHArmACeuTiCAl OrgAniC CHemiSTry
Arenes can be divided into two categories:
1. Arenes containing one benzene ring and a side chain
2. Arenes containing more than one benzene ring either linked directly or through one or more carbon
atom
Arenes containing one benzene ring and a side chain
Depending upon the nature of the aliphatic side chain, these arenes are further classied as
Monoalkyl benzenes Dialkylbenzene
CH
3
CH
Toluene
3
C2H
5
Ethyl benzene
H3C C CH
t
-Butyl benzene
CH
3
o/m/p
3
-xylene
CH
3
Alkenyl benzene
These arenes contain unsaturated alkene group on the benzene ring with the general formula C6H5CnH
CH CH
2
Phenyl acetylene 1-Phenyl propene
CH
CH CH
3
Alkynyl benzene
These arenes contain an alkyne group on benzene ring with the general formula C6H5CnH
2n-3
.
For example,
C CH
C
6H5
Phenyl acetylene
2n-1
Arenes containing more than one benzene ring either linked directly or through one or more carbon atom
CH
2
Diphenyl methaneBiphenyl