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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5852_Библиотеки_им_академика_М_И_Перельмана.pdf
C H a P T e r 8 Dienes
Para-aminobenzoic acid
PABA
2-ethylhexyl-4-(dimethylamino)-benzoate
(Padimate O)
H2N COH
O
CH2CH
3
CH3O
2-Ethylhexyl-(E)-3-(4-methoxyphenyl)-2-propenoate
(Giv Tan F)
OCH2CHCH2CH2CH2CH
3
O
(CH3)2N COCH2CHCH2CH2CH2CH
3
O CH2CH
3
8.5.6 Physiological Effect of 1,3-Butadiene
It is suspected as human carcinogen, 1,3-butadiene induces physical deformity (teratogen). excessive and
prolonged exposure can affect many areas in the human body; blood, brain, eye, heart, kidney, lung, nose
and throat. Women are more sensitive towards carcinogenic effects of butadiene than men. animal studies
have shown breathing butadiene during pregnancy can increase the number of birth defects.
Learning Plus
Skin colour darkens in the sunlight because it stimulates the pigment
melanin. Melanin absorbs UV light. Sunscreen can protect skin against
UV light. First commercially available UV-absorbing sunscreen was
PABA. Giv Tan F is another better sunscreen because it absorbs UV-A
and UV-B light. The amount of protection is judged by sun protection
factor (SPF). Higher is the SPF, higher is the sun protection.
321
322
Br2 /500°C
CH3CH CH
2
BrCH2CH CH
2
alc KOH
AllenePropene
CH
2
CH
2
C
PHarmaCeuTICal OrganIC CHemIsTry
REVISION QUESTIONS
1. Write a note on stability of conjugated dienes.
2. Discuss the molecular orbital structure of 1,3-butadiene.
3. How is 1,3-butadiene prepared? Describe its important reactions.
4. What happens when
(a) 1,3-Butadiene is treated with bromine in carbon tetrachloride
(b) 1,3-Butadiene is treated with HBr
ans: (a) a mixture of 3,4-dibromo-1-butene and 1,4-dibromo-2-butene is formed. For reaction equation,
see text.
(b) a mixture of 3-bromo-1-butene and 1-bromo-2-butene is formed. For reaction equation, see text.
5. give a mechanism for the following reactions
(a) For the reaction of 1,3-butadiene with HBr
(b) For the reaction of 1,3-butadiene with bromine
(a) 1,3-Butadiene from 1-butene
(b) allene from propene
ans: (a) The following steps are involved:
(b) Following steps are involved:
6. How will you synthesize
7. How will you distinguish between 1,3-butadiene and n-butane?
C H a P T e r 8 Dienes
Br
CCl
4
(red) (colourless)
(colourless)
CH2CHCH CH2 + Br
2
CHCH2Br
CH
2
+ BrCH2CH
BrCH2CHCH
ans: 1,3-Butadiene immediately decolourizes the red colour of Br2 in CCl4 solution. n-Butane does not
react with this reagent.
8. Write a note on stability of conjugated dienes.
MULTIPLE CHOICE QUESTIONS
1. 1,2-Butadiene has
(a) only sp hybridized carbon atoms (b) only sp2 hybridized carbon atoms
(c) only sp3 hybridized carbon atoms (d) sp, sp2 and sp3 hybridized carbon atoms
2. How many sigma (s) bonds are there in 1,3-butadiene?
(a) 3 (b) 6
323
(c) 9 (d) 12
3. Propadiene, CH2 C
(a) a planar compound (b) a cumulated diene
(c) an isolated diene (d) a conjugated diene
4. 1,3-Butadiene is
(a) a planar compound (b) a cumulated diene
(c) an isolated diene (d) a conjugated diene
5. Which of the following compounds have planar molecular?
(a) 1,3-Butadiene (b) Diethyl ether
(c) 1-Butene (d) allene
6. Which of the following molecular formulas will correspond to an alkene with two double bonds?
(a) C4H10 (b) C5H
(c) C6H10 (d) C8H
, is
CH
2
12
8
324
PHarmaCeuTICal OrganIC CHemIsTry
7. 1,3-Butadiene reacts with bromine to mainly give
(a) 3,4-Dibromo-1-butene (b) 4-Bromo-1-butene
(c) 1,4-Dibromo-2-butene (d) 1-Bromo-2-butene
8. Catalytic hydrogenation of 1,3-butadiene gives which one of following as main product
(a) Butene-1 (b) Butene-2
(c) Butane (d) Butyne
9. The major product obtained when HBr reacts with 1,3-butadiene is
(a) 1-Bromo-2-butene (b) 3-Bromo-1-butene
(c) Both the above in amounts (d) either of the two above
10. Diels–alder reaction between 1,3-butadiene and ethene gives
(a) 1,4-Cyclohexadiene (b) Cyclohexene
(c) Cyclohexane (d) Cyclohexyne
ANSwERS
1. (d) 2. (c) 3. (b) 4. (d) 5. (a) 6. (c) 7. (c) 8. (b) 9. (b) 10. (b)
5
Benzene and
Polynuclear
comPounds
9
Science, in the very act of solving problems,
creates more of them.
–Abraham Flexner
Chapter Outline
9.1 Introduction, 9.2 Nomenclature of Aromatic Compounds, 9.3 Isomerism of Benzene Derivatives, 9.4 Preparation of Benzene,
9.4.1 Commercial Preparation of Benzene, 9.4.2 Laboratory Methods of Preparation of Benzene, 9.5 Properties of Benzene, 9.5.1 Physical
Properties of Benzene, 9.5.2 Chemical Properties (Reactions of Benzene), 9.5.3 Physiological Effects of Benzene, 9.6 Structure of Benzene,
9.6.1 Kekule Ring Structure of Benzene, 9.6.2 Resonance Structure of Benzene, 9.6.3 Molecular Orbital Structure of Benzene, 9.7 Aromatic
Electrophilic Substitution (Characteristic Aromatic Reaction), 9.7.1 Electronic Mechanism of Electrophilic Monosubstitution in Benzene Ring,
9.7.2 Mechanisms of Some Electrophilic Substitution Reactions of Benzene, 9.7.3 Isotopic Effect and Evidence in Support of Two-Step
Electrophilic Aromatic Substitution, 9.8 Theory of Reactivity, 9.9 Directive Influence of Groups in Electrophilic Substitution, 9.9.1 Orientation,
9.1 INTRODUCTION
Benzene and other aromatic compounds are conjugated cyclic polymers. Their chemical reactivity and
model aromatic compound.
6H6
9.9.2 Theory of Orientation Based on Stability of Carbonium Ion
.
nH2n-6
9.2 NOMENCLATURE OF AROMATIC COMPOUNDS
326
Cl
NitrobenzeneChlorobenzene
NO
2
SO2OH
Benzene sulphonic acid
CH
3
OH
Toluene Phenol
Br
Br
NO
2
NO
2
o-Dibromo benzene
1,2-Dibromo benzene
m-Dinitro benzene
1,3-Dinitro benzene
o, m or p (i.e.
ortho, meta or para
special names.
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
o-Xylene m-Xylene p-Xylene
OH
NH
2
OH
COOH CHO
NH
2
o-Aminophenol m-Hydroxybenzoic acid p-Aminobenzaldehyde
NO
2
Cl Cl
Br
m-Chloronitrobenzene m-Bromochlorobenzene
CH
3
1,2,4-Trichlorobenzene 2,4-Dinitrotoluene
327
328
CH
3
CH
3
o-Xylene
or
1,2-Dimethylbenzene
CH
3
CH
3
m-Xylene
or
1,3-Dimethylbenzene
CH
3
CH
3
p-Xylene
or
1,4-Dimethylbenzene
CH2CH
3
Ethylbenzene
1-Methylnaphthalene
CH
3
CH
3
2-Methylnaphthalene
9.3 ISOMERISM OF BENZENE DERIVATIVES
mono-substitution products of benzene do not show
isomerism.
di-substitution
products of benzene show positional isomerism. These three isomers are called ortho (om
para (p
up.
COONa
+ NaOH + Na
2CO3
CaO
Heat
BenzeneSodium benzoate
OH
+ Zn + ZnO
Distillation
Phenol Benzene
9.4 PREPARATION OF BENZENE
9.4.1 Commercial Preparation of Benzene
1. Ammoniacal liquor
9.4.2 Laboratory Methods of Preparation of Benzene
329
1. By distillation of sodium benzoate:
2. From benzene derivatives
a. Reduction of phenol:
330
+ 2H + HCl
Ni–Al alloy
NaOH
Benzene
Chlorobenzene
Cl
Cl
Chlorobenzene
MgCl
Phenyl
magnesium
chloride
+ Mg + Mg
Dry ether
Benzene
OH
Cl
H2O
SO3H
Benzene sulphonic acid
+ HOH
+ H
2SO4
Benzene
150–200°C
HCl, pressure
Steam
N2Cl
+ 2H
+ N
2
+ HCl
SnCl
2
NaOH
Benzene
From chlorobenzene:
hydrogen.
c. By rst preparing Grignard reagent of chlorobenzene and then hydrolysis
d. From benzene sulphonic acid
e. From benzene diazonium chloride:
3. From acetylene:
o