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PHARMACEUTICAL CHEMISTRY




Alkanes, Alkenes, Alkynes, Alkyl Halides, Alicyclic Hydrocarbons, Alcohols,

Ethers and Epoxides, Aldehydes and Ketones, Carboxylic Acids and their
Functional Derivatives




Sameena Bano

Department of Chemistry
Faculty of Science

Jamia Hamdard
New Delhi-110062




(24.07.2007)


CONTENTS
Alkanes
Alkenes or Olefins
Alkynes
Alkyl Halides
Alicyclic Hydrocarbons or Cyclo Alkanes
Alcohols
Ethers
Epoxides
Aldehydes and Ketones
Carboxylic Acids and Their Functional Derivatives








Keywords
Alkanes, alkenes, alkynes, alkyl halides, alicyclic hydrocarbons, alcohols, ethers, epoxides, aldehydes, ketones and
carboxylic acids







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Alkanes
The alkanes are simplest and least reactive class of organic compounds, because they contain
only carbon and hydrogen and they have no functional groups. They also referred to as Paraffins.
Alkanes are the saturated hydrocarbon with general formula (CnH2n+2). Alkanes contain only
single covalent carbon-carbon (C-C) and Carbon –Hydrogen(C-H) bonds. Each carbon atom of
alkanes is sp3 hybridized.




Structure of Methane Structure of Ethane

All C-C and C-H bonds are σ bonds and every C-H and C-C bond lengths have the value 1.09Ao
and 1.54Ao respectively. All bond angles are tetrahedral (109.5o) because of tetrahedral position
of the four bonds of carbon, the C-C chain is zig-zag and not linear some examples of the
alkanes are

CH3-CH2-CH3

CH3-CH2-CH2-CH3

Ethane [ C2H6] Propane [C3H8]

Butane [C4H10]

Methane [CH4]

CH3-CH2-CH2-CH2-CH3

Pentane

C

H

H
H

H C

H

C
H

H

H

H
H



First three members do not exhibit isomerism but the higher members [butane and onwards]
exhibit chain isomerism.

Iso butane[C4H10] Iso pentane [ C5H12] Neo pentane [C5H12]

CH3 CH CH3

CH3
CH3 CH CH2 CH3

CH3
CH3 C CH3

CH3

CH3


Methods of preparations:
i) Hydrogenation of unsaturated hydrocarbons: Alkenes or alkynes react with hydrogen in
presence of catalyst (Ni, Pt or Pd) at 200-300o C to give alkanes. (Sabatier and Senderen’s
reaction).

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This method is useful for the preparation of simple ethers only.

3) Williamson Ether Synthesis: This is the most important industrial and laboratory method of
preparation of ethers. It involves the treatment of sodium alkoxide with an alkyl halide. Both
symmetrical unsymmetrical ethers can be prepared by this method.




R-ONa NaX+ +
+-

Alkyl halideSod. alkoxide Symmetrical ether
R-O-RX-R



R-ONa R-O-R' NaX+ +
unsymmetrical ether

+-
X-R'

Sod. alkoxide Alkyl halide


+ +

+-
C2H5ONa Br-C2H5 C2H5-O-C2H5 NaBr

Diethyl ether


+ +

+-
CH3ONa Br-C2H5 CH3-O-C2H5 NaBr

Ethyl methyl ether

Tertiary and Secondary alkyl halides undergo elimination reaction with sodium alkoxide [strong
base]. Thus to introduce a tertiary group it will be better to take this group as a base, not as a
tertiary halide. For example

R-ONa
CH3

CH3
CH3

Cl CH3 C CH2

CH3

+ ClH


Thus for preparing (CH3)3C-O-C2H5 , we should start with (CH3)3C-ONa
+-

and C2H5Br.

Mechanism: It follows SN2 mechanism. Displacement of halide ion by alkoxide ion.

R-ONa R X
SN2

R-O-R NaBr++
+-


5)Action of Diazomethane on Alcohols: Ethers can be prepared by treatment of primary or
secondary alcohols with diazomethane in presence of flouroboric acid as a catalyst.

R-OH CH2N2
HBF4

R-O-CH3 N2++

C2H5-OH CH2N2+ HBF4 C2H5-O-CH3 N2+


But this method is only useful for the preparation of methyl ethers.

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Properties:
Physical properties:

1) Ethers are highly volatile and inflammable substances.
2) Except dimethyl ether and ethyl methyl ether, which are gases all are pleasant

smelling colourless liquids.
3) Their boiling points gradually increase with the increase in molecular weight. But

ethers have lower boiling points than isomeric alcohols because they are
incapable of forming inter molecular hydrogen bonds due to the absence of –OH
groups.


Ethers are sparingly soluble in water since their oxygen atom is not capable of forming H-bond
with hydrogen with hydrogen atom of water molecule.

Chemical Properties:
Ethers are much less reactive compounds because they are quite stable. They do not react with
active metals, strong bases like NaOH, reducing and oxidizing agents.
1) Halogenations: When ethers react with chlorine or bromine substitution preferentially at -
Carbon takes place.
For example:

CH3-CH2-O-CH2-CH3
Cl2

dark
CH3-CH-O-CH2-CH3 CH3-CH-O-CH-CH3

Cl2

dark

Cl Cl Cl


- Chloro diethyl ether , 1- Dichlorodiethyl ether.

The extent of substitution depends on reaction conditions.

2) Basic Nature: Ethers react with cold concentrated sulphuric acid or HCl to give oxonium salt.
Their basic nature is due to the presence of two lone pairs on oxygen atom.

ClR O R..
..

+ ClH R O+ R
H

..
-

oxonium ion

cold



This property is used to separate ethers from ethyl bromide and to distinguish from alkanes.
Since alkanes do not react with acids.

3) Formation of peroxides (Auto oxidation): On standing in contact with air ethers combine
with oxygen to form peroxide which is highly explosive.

H2CH3C O CH2CH3+ O2 long
contact

(CH3CH(OOH).OC2H5


These peroxides decompose violently at high temperature. Thus ethers should be always be
purified before distillation. When ethers that contains peroxide is distilled, at the end of

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R C OR'

O

R C O

O
-

R
..
.. + OHH +



General reactions of esters are given below.

1) Hydrolysis:
a) Acid hydrolysis: Esters are hydrolyzed in presence of acid catalyst (H2SO4) or HCl) to give
parent carboxylic acid and alcohol.

R C OR'

O

+ R C OH
O

+ R'OH
Ester Carboxylic acid Alcohol

OH2
H

+

reflux


b) Alkaline hydrolysis: The alkaline hydrolysis of ester to form sodium or potassium salt of
carboxylic acid and alcohol is referred to as Saponification.

R C OR'

O

+ R C ONa
O

+ R'OH

CH3COOC2H5 + CH3 C ONa
O

+ C2H5OH

NaOH

NaOH

Ester Sodium carboxylate Alcohol

Ethyl acetate Sodium acetate Ethyl alcohol

+-

- +




2) Reaction with Ammonia:

R C OR'

O

+ NH2H R C NH2
O

+ R'OH

CH3COOC2H5 + NH2H CH3 C NH2
O

+ C2H5OH

Ester Amide Alcohol

Ethyl acetate Acetamide


3) Reduction:



R C OR'

O
LiAlH4 / Ether

or
Na / C2H5OH

R-CH2OH R'OH+
Alcohols

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CH3 C OCH3

O LiAlH4 / Ether

or
Na / C2H5OH

CH3-CH2OH CH3OH+
Ethyl alcohol Methyl alcohol


4) Reaction with Grignard Reagent: Esters with Grignard reagent first gives ketone which on
further reacting with another molecule of the G.R gives tertiary alcohol.

R C OR'

O
R"-MgX

R C OR'

OMgX

R"

-OR'
R C R"

O

Ketone

R"MgX
R C R"

OMgX

R"

H2O R C R"
OH

R"

3o alcohol


5) Claisen Condensation: Esters containing α-hydrogen atom undergo condensation reactions to
form β-ketoesters, in the presence of strong base. This reaction is known as .

CH3 C OC2H5

O

+ H CH2 C OC2H5
O

C2H5ONa

-C2H5OH
CH3 C

O

CH2 C OC2H5

O

Ethyl acetoacetate
Mechanism: Following steps are involved.

H CH2 C OC2H5

O

C2H5O
-

H2C C OC2H5

O
-

CH3 C OC2H5

O



CH3 C

O
-

CH2 C OC2H5

O

OC2H5
Ethyl acetoacetate

-
CH3 C

O

CH2 C OC2H5

O
-C2H5O


(β-keto ester)


Suggested Readings:

Organic Chemistry by I. L. Finar, vol. 1, 6thedition
Organic Chemistry by Paula Yurkanis Bruice, 3rd edition.
Organic Chemistry by Robert T. Morrison and Robert Neilson Boyd, 6th edition.
Organic Chemistry by K. Peter C. Vollhardt and Neil E. Schore, 4th edition.

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