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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5574_Библиотеки_им_академика_М_И_Перельмана.pdf
Alkyl Halides
4H9
4H9
(a) Vinyl chloride is less reactive than ethyl chloride
(b) Allyl chloride is more reactive than vinyl chloride
12 reactions of alkyl halides.
hol.
tert tert
alcohol.
E2 and E1 reaction of alkyl halides.
421
12. How will you convert ethyl bromide into the following compounds
(a) n
(a) Isopropyl bromide from n
(b) Propionic acid from ethyl bromide
(c) Vinyl bromide from ethyl alcohol
2O/H+.
4H9
H, which was different than the compound when n-butyl bromide was reacted with sodium.
422
MULTIPLE CHOICE QUESTIONS
1. Which of the following reagents cannot be used to prepare an alkyl chloride from an alcohol
2
2
5
24 to give
2
4. Isopropyl bromide reacts with alcoholic KOH to give
(a) Propene (b) Isopropyl alcohol
(c) Propane (d) n-Propyl alcohol
2
6. Alkyl halides undergo
(c) Propanone (d) Propyne
9. Which alkyl halides react with readily by nucleophilic substitution
2 2
2 2F
Alkyl Halides
2 reaction
2
) )
1 mechanism
(a) Methyl chloride (b) Isopropyl chloride
tert
(a) Alcoholic KOH, methyl iodide and sodium metal
(b) Alcoholic KOH, methyl iodide and primary amine
(c) Alcoholic KOH, chloroform and primary amine
(d) Alcoholic KOH, methyl alcohol and primary amine
(c) Acetone (d) Propene
423
15. n-Propyl iodide reacts with sodium ethoxide to give
22 222
2 22
12, E1 or E2
mechanism
(a) tructure of the alkyl halides (b) oncentration of reagents
(c) ature of nucleophile (d) All of these
17. Which of the following compounds has been suggested as causing depletion of ozone layer in the
upper stratosphere
4 2F
4 2
2
2
2F2) is used as a
(a) ocal anaesthetic (b) ry cleaning agent
(c) Refrigerant (d) isinfectant
424
19. Which of the following poisonous gas is formed when chloroform is exposed to light and air
(a) Mustard gas (b) arbon monoxide
(c) Phosgene (d) hlorine
20. Which of the following does not give iodoform test
2 2 (b) cis
(c) trans )2
2
22. The reaction between primary amine, chloroform and alcoholic potash is called
(a) Wurtz reaction (b) Prankland reaction
HO is warmed with aqueous sodium
carbonate and iodine solution the product is
HO
25. Which of the following metal powder is used to convert trichloromethane into acetylene by heating
the latter with it
22
hloropropene
2 is
2 mechanism proceeds through the intervention of
Alkyl Halides
2O
In the above reaction, reactivity of different alcohols is of the order
(a) oth aliphatic and aromatic primary amines
(b) Aromatic primary amine
(c) Aliphatic primary amine
(d) Aliphatic secondary amine
2
2
425
known as
romopropane
romopropane (d) All of these
ANSWERS
1. (c) 2. (c) (a) 4. (a) 5. (b) 6. (c) 7. (b) (b) 9. (b) 10. (a)
11. (d) 12. (c) (c) 14. (b) 15. (b) 16. (d) 17. (b) (c) 19. (c) 20. (d)
21. (d) 22. (d) (b) 24. (c) 25. (d) 26. (c) 27. (c) (c) 29. (a) (a)
(a) (c) (b)
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12
ALCOHOLS
Reason, observation, and experience–
the Holy Trinity of science.
HH
C
H
C
O
H
H
H
–Robert G. Ingersoll
Chapter Outline
12.1 Introduction, 12.2 Classification of alcohols, 12.2.1 Monohydric Alcohols, 12.3 Isomerism, 12.4 General Methods of Preparation of
12.8 Distinction between 1º, 2º, 3º Alcohols, 12.9 Ethylene Glycol, 12.9.1 Preparation of Ethylene Glycol, 12.9.2 Physical Properties,
12.1 INTRODUCTION
The organic compounds containing one or more hydroxyl groups attached to sp3 carbon atoms are called
alcohols. They are very important organic compounds because they are used to prepare a number of other
organic compounds. Therefore, in this chapter, we shall study some of the important aspects of the chemistry of alcohols.
12.2 CLASSIFICATION OF ALCOHOLS
All the alcohols can be broadly subdivided into two categories, i.e. aliphatic alcohols and aromatic alcohols.
1. Aliphatic alcohols: These aliphatic hydroxy compounds in which the hydroxyl group is linked to an
aliphatic carbon chain are called aliphatic alcohols.
For example,
Alcohols, 12.5 Structure of Alcohol, 12.6 Physical Properties, 12.7 Chemical Properties,
12.9.3 Chemical Properties, 12.10 Glycerol (1,2,3-Propanetriol), 12.10.1 Preparation,
12.10.2 Physical Properties, 12.10.3 Chemical Properties
OH
CH
OH
Methanol
(Methyl alcohol)
C
H
OH
Ethanol
(Ethyl alcohol)
—
CH
2-Propanol
(Isopropyl alcohol)
—
CH
—
CH
Ethanol (ethyl alcohol)
2. Aromatic alcohols: Those aromatic hydroxy compounds in which the hydroxyl group is linked to the
side chain of an aromatic hydrocarbon are called aromatic alcohols.
For example,
CH OH
2
Phenyl methanol
(Benzyl alcohol)
——
HO CH CH
1-Phenyl ethanol
α
( -Phenylethyl alcohol
3
2-Phenyl ethanol
( -Phenylethyl alcohol))
——
CH CH OH
22
β
428
( )Monohydric alcohol
Trihydric alcohol
)
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
They can be further classied as mono-, di- and trihydric alcohols depending upon whether they contain
one, two or three hydroxyl (–OH) groups. Alcohols which contain four or more hydroxyl groups attached
to the sp
3
carbon atoms are called polyhydric alcohols.
H
—
— —
CH OH
—
H
Methyl alcohol
(Methanol)
—
C OHH
—
2
—
C OHH
2
Ethylene glycol
(1,2-Ethanediol)
(
Dihydric alcohol
(1,2,3-Propanetriol )
(
—
C OHH
—
2
—
CH OH
—
—
C OHH
2
Glycerol
C OHH
—
2
(CHOH)
—
C OHH
2
Sorbitol or Mannitol
(
Polyhydric alcohol
)
4
)
12.2.1 Monohydric Alcohols
The organic compounds derived from alkanes by the replacement of a hydrogen atom by a hydroxyl group are known as monohydric alcohols or alkanols. They may be represented by the general formula R–OH or
nH2n+1
—
OH, where R stands for an alkyl group.
C
Classification of monohydric alcohols
Monohydric alcohols are classied as primary (1º), secondary (2º) and tertiary (3º) depending upon
hydroxyl group attached to primary, secondary and tertiary carbon atom, respectively.
—
Methyl alcohol
(1°) (Μethanol)
—
—
Isopropyl alcohol (2°)
(2-Propanol)
tert
(2-Methyl-2-propanol)
—
—
—
—
-Bytyl alcohol (3°)
The characteristic or functional groups of primary, secondary and tertiary alcohols are as follows:
Type of alcohol Primary or 1º Secondary or 2º Tertiary or 3º
Characteristic group
—
CH OH
—
CHOH
2
—
—
C OH
—
—
—
Nomenclature of monohydric alcohols
1. Common system: The common name is derived by adding the sufx alcohol to the name of the alkyl
group.
2. Carbinol system: According to this system, methyl alcohol is known as carbinol and the other alco-
hols are named as alkyl derivatives of carbinol.
C H A P T E R 12 u Alcohols
3
—
OH
3,5-Dimethylheptan-3-ol
(Allyl alcohol)
(Propargyl alcohol)
3. IUPAC system: In this system
a. The parent chain is numbered in such a way as to give smallest possible number to the carbon
atom bearing the hydroxyl group.
b. The letter e of the alkane is replaced by ol.
The nomenclature of some alcohols is given below:
Alcohol Common name Carbinol name IUPAC name
429
—
H C OH
—
3
3
3
C
3
C
3
CH
CH—CH
—
—
CH
—
CH
—
CH
CH
—
—
C
—
—
H C
H C
CH
H
CH
—
3
2
3
3
2
—
OH
—
CH
CH
CH
—
OH
2
3
—
—
CH
2
2
—
OH
2
Methyl alcohol Carbinol Methanol
n-Propyl alcohol or pro-
pyl alcohol
Ethyl carbinol 1-Propanol
Isopropyl alcohol Dimethyl carbinol 2-Propanol
n-Butyl alcohol or Butyl
OH
alcohol
n-Propyl carbinol 1-Butanol
Isobutyl alcohol Isopropyl carbinol 2-Methyl-1-propanol
tert-Butyl alcohol Trimethyl carbinol 2-Methyl-propan-2-ol
IUPAC names of a few other substituted alcohols are given below:
OH
—
3
4
—
—
—
2
C H
2 5
3
can be written as
5
—
—
H C CH CH C CH
—
3
6
C H
2 5
5
4
—
H C CH
3
—
2 33
2
—
C
C
H
H C
—
6
CH
—
2
7 1
CH
3
3,5-Dimethylheptan-3-ol
OH
—
CH
—
CH
—
2
3
12.3 ISOMERISM
Alcohols exhibit both structural (three types) and stereoisomerism.
Structural isomerism
1. Chain isomerism: Alcohols exhibit chain isomerism due to the presence of different types of car-
bon chains. It is shown by members containing four or more carbon atoms, e.g. molecular formula
C
OH has following three chain isomers:
4H9
—
— —
—
Prop-2-en-1-ol
3
—
—
—
12
—
C CCH H OH
Prop-2-yn-1-ol
—
2
430
(1-Propanol)
(2-Propanol)
PH A R M A C EUT I C A L O R G ANIC C H E MIST RY
a.
—
—
—
n
-Butyl alcohol
—
b.
—
— —
H C CH C3H OH
CH
Isobutyl alcohol
—
2
3
c.
2. Position isomerism: This isomerism is due to different positions occupied by
carbon chain, e.g. C3H7OH has two position isomers.
C
H
tert
CH
—
—
—
OH
—
CH
-Butyl alcohol
—
group in the
—
a. b.
—
n
-Propyl alcohol
—
Isopropyl alcohol
—
—
—
3. Functional isomerism: Saturated monohydric alcohols are isomeric with ethers, the general formula
of both being C
O. For example, C2H6O represents both ethyl alcohol and dimethyl ether, which
nH2n+1
have different functional groups:
a. CH
3
Ethyl alcohol
(Functional group
b. C
3H7
Propyl alcohol
(Propanol)
(Functional group
—
—
CH
2
(Ethanol)
— OH
—
OH
—
OH)
OH)
(Functional group
(Functional group
—
CH
O — CH
3
3
Dimethyl ether
(Methoxy methane)
— O —
CH
— O — C2H
3
5
Ethyl methyl ether
(Methoxy ethane)
—
O —)
)
Stereoisomerism
Alcohols having chiral carbon can exhibit optical isomerism, e.g. sec-Butyl alcohol is known to exist in two
optical isomeric forms which are nonsuperimposable mirror images of each other. (CH
CHOHCH2CH3 has
3
one chiral carbon atom.) The enantiomeric forms of secondary butyl alcohol have been shown below:
H C *C OH
3
Mirror
H
—
— —
—
C H
2 5
H
—
—
C
—
—
H
2 5
HO C CH
Enantiomers of sec-butyl alcohol
3