This document provides an introduction to organic chemistry. It defines organic compounds as those containing carbon, originally thought to originate only from living organisms (vital force theory). This theory was disproven when Wohler synthesized urea from inorganic compounds in 1828. Organic chemistry is now defined as the study of carbon compounds, which are found in both living and non-living systems. Key topics covered include classification of organic compounds into open chain and cyclic types, functional groups like alkyls, and the unique properties of carbon that allow for large numbers of organic structures.

1. ORGANIC CHEMISTRY
Class XI
Department of Chemistry
Tilottama Campus,
Tilottama-2, Nepal

2. Organic Chemistry
Introduction
The branch of science that deals with structure,
composition, preparation, properties and uses of
various chemical compounds is known as chemistry.
There are main two classes of chemical
compounds i.e. organic and inorganic compounds.
The chemical compounds which were obtained from
mineral and earth crust are called inorganic
compounds. For example, salt, marble, glass, alum,
metals, non metals etc.

3. The compounds which were obtained from
vegetable and animal origin are called organic
compounds. For example, carbohydrate, fat, oil,
protein, vitamin petroleum product etc.
This classification of chemical compound was
first given by a Swedish chemist J.J. Berzelius in 18th
century. The word organic has been derived from
‘organism’ which means living body. Thus the
compounds which were originated from living body
i.e. plants, animals and micro-organism are called
organic compounds and the systematic study of such
compounds is called organic chemistry.

4. Vital force theory
(Origin of organic compounds)
In the early stage of development of chemistry
it was considered that, all organic compound could
be originated from plants and animals only through
some mysterious natural force. This concept of
involvement of living being in the production of
organic compounds for the first time was proposed
by Berzelius in 1815 which is called as ‘vital force
theory’.
The word vital has been derived from Latin word ‘vita’
which means life. Therefore, the organic compound could
only produced by some mysterious natural life force (god
force) existing in living organism.

5. The laboratory synthesis of organic compound was
considered impossible due to absence of vital force
or living force.
Failure of Vital force theory
The vital force theory was in belief for long time.
Later on in 1828, a German chemist Friedrich Wohler
obtained typical organic compound ‘urea’ from inorganic
compound ‘ammonium cyanate’ on heating.
NH₄Cl + KCNO ⟶ NH₄CNO + KCl
Ammonium cyanate
NH₄CNO ⟶ NH₂-CO-NH₂
Urea
(Organic compound)

6. This synthesis of an organic compound from
inorganic compound broke down the old concept of
origin of organic compound i.e. vital force theory is
failed out and is discarded.
Hennel (1828) ⟶ Ethyl alcohol (C₂H₅-OH)
Kolbe (1845) ⟶ Acetic acid (CH₃-COOH)
Berthelot (1856) ⟶ Methane (CH₄)
Now a days more than 95% of organic compounds
are synthesized in lab by using different chemicals
from artificial method.

7. Modern definition of organic chemistry
After the failure of vital force theory, the new
concept of organic compound is developed. So
organic compound should be defined with wider and
modern concept.
Detail investigation of organic compound
indicates that all organic compound contains
covalently bonded carbon which always contains
hydrogen and sometimes other elements like O, N, S,
P, X and some metals. Hence hydrocarbons and their
derivatives are called organic compounds. For
example, carbohydrate, protein, vitamin, fat, oil,
hormone, acid, dyes, drug, explosive, rubber, plastic,
petroleum product etc.

8. The branch of chemistry that deals with
hydrocarbons and their derivatives is called organic
chemistry. Simply, the study of carbon compounds
is called organic chemistry.
CO, CO₂, H₂CO₃, metal carbonates, metal bicarbonates,
metal cyanides etc are inorganic compounds.
Reason for separate study of organic compounds
1. Large numbers of organic compounds
(Carbon compounds)
1. Unique physical and chemical properties
2. Unique nature of carbon

9. Difference between organic and inorganic compounds
Organic compounds
• They are made up of C, H and
some other elements.
• Mostly occurs in living
organism.
• They are more than 10 billion.
• They are mostly soluble in
organic solvents.
• They show covalent bond.
• They have low melting and
boiling point.
• They show isomerism.
Inorganic compounds
• They are made up of almost
all elements.
• Mostly occurs in non-living
matters.
• They are less than 1 lakhs.
• They are mostly soluble in
water.
• They show ionic bond.
• They have high melting and
boiling point.
• They do not show isomerism.

10. .
Organic compounds
• They are directional in nature.
• They form homologous series
of same functional group.
• They show molecular reaction
which is very slow.
• They are combustible.
• Their solution is non-
conductor of electricity.
• Carbon atom can show
catenation property.
Inorganic compounds
• They are non-directional in
nature.
• They do not form any types
of homologous series.
• They show ionic reaction
which is very fast.
• They are non-combustible.
• Their solution is conductor of
electricity.
• No any element can show
catenation.

11. Source of organic compounds
1. Plants and animals: Carbohydrate, fat, protein,
vitamin, oil, resin, rubber, starch, cellulose etc.
2. Natural gas and petroleum: Cooking gas, diesel,
petrol, kerosene, methane, ethane, benzene,
toluene, anthracene etc.
3. Coal: Coke, coal-tar, starting material for dyes,
drugs, perfumes etc.
4. Fermentation: Alcohol, acid, vitamin, drugs,
antibiotics etc.
5. Synthesis: Dyes, drug, explosive, rubber, plastic,
fiber, polymer etc.

12. Importance of organic compounds
1. Food: Carbohydrate, protein, fat, oil, vitamin,
milk, egg, meat, cereals, fruits etc.
2. Clothes: Cotton, silk, wool, nylon, terylene,
polystyrene, cellulose etc.
3. Medicinal drugs: Antibiotics, pain killer, vitamin,
antipyretics, antiseptics, quinine etc.
4. Plastics, dyes and explosives: Polyethenes,
polystyrene, rubber, PVC, congo-red, aniline
blue, aniline yellow, azodyes, TNT, TNG, picric
acid, gun-cotton etc.

13. 5. Fertilizers, pesticides and insecticides: NPK, DDT,
BHC etc.
6. Petroleum products: Cooking gas, gasoline,
diesel, petrol, kerosene, air fuel, lubricating oil,
gelly wax etc.
7. Cosmetics: Perfumes, face cream, hair oil, nail
polish, beauty soap, skin lotion, shampoo etc.
8. Industrial goods: Alcohol, paper, soap, detergent,
color, paint, varnishes etc, all are organic
compounds.

14. Unique nature of carbon
1. Terta-covalency of Carbon
Atomic number of carbon is 6 which belongs to
group IV-A and second period in periodic table.
Electronic configuration of C (6) = 1s²,2s²2p²
C-atom in ground state =
Only valence electron take part in chemical bond
formation.
C-atom in excited state =
Sp³-hybridization

15. Carbon atom has six electrons in which two are
inner electrons and rest four are valence electrons
which are distributed to 2s and 2p orbital.
In excited state, one electron from 2s orbital
excites to 2p orbital and becomes four unpaired
electron in valence shell. Which accounts for tetra-
covalency of carbon atom. This carbon atom
acquires octet state by sharing these four unpaired
electrons with four electrons of other atom during
chemical bond formation and thus shows tetra-
covalency.

16. Similarly carbon atom can form carbon to carbon
single, double and triple bond in a series of organic
compounds. For example,

17. 2. Catenation property
Carbon is only one element in periodic table
which can form millions of carbon compound with
varying number of carbon atom. It has a unique
property of linking itself to another carbon atom to
give several open chain as well as cyclic compounds.
This property of self linking of carbon atom with each
other to form long chain compound is called
catenation property.
This property is favoured by the formation of carbon to
carbon strong covalent bond. Each carbon atom can form
single, double and triple bond and can combined with 2, 3, 4,
or 5 C-atom through covalent bond to form variety of linear,
branched or cyclic compounds.

18. …

19. Alkyl groups
An alkyl group is formed by removing one
hydrogen atom from alkane molecule. They are
named by adding yl to ane of alkane. For example,
alkane –ane + yl = alkyl.
R-H ⟶ -R + H CH₄ ⟶ -CH₃ + H
Alkane Alkyl Methane Methyl
-CH₂CH₃ = ethyl
-CH₂CH₂CH₃ = n-propyl
-CH₂CH₂CH₂CH₃ = n-butyl

20. Structural, Contracted and Bond line formula
The formula that indicates how the atoms are
bonded in a molecule is called structural formula.
The formula in which hydrogen atoms are
condensed with carbon is called contracted formula.
The formula in which carbon and hydrogen are not
shown and are represented by a line is called bond
line formula. For example,
Structural Contracted Bond line
formula formula formula

21. Organic compounds
[A] Open chain or [B] Cyclic chain or Acyclic
compound ring compound
(a) Alkanes (a)Homocyclic (b) Heterocyclic
(b) Alkenes
(c) Alkynes (i) Alicyclic (i) Heteroalicyclic
(ii)Aromatic (ii) Heteroaromatic

22. Classification of organic compounds
[A] Open chain or acyclic organic compounds
The compounds which consist of open chain of
carbon atom are called open chain or acyclic or
aliphatic organic compounds. The carbon chain may
be linear or branched.
(a)Alkanes:
The open chain organic compounds which consist if
carbon to carbon single bond (C-C) are called
alkanes.

23. (b) Alkenes
The open chain organic compounds which consist of
carbon to carbon double bond (C=C) are called
alkenes. For example,
(c) Alkynes
The open chain organic compounds which consist of
carbon to carbon triple bond (C≡C) are called
alkynes. For example,

25. [B] Closed chain or cyclic organic compounds
The compounds which consist of one or more
cyclic chain of carbon atom are called closed chain
or cyclic chain compounds or ring compounds.
(a) Homocyclic organic compounds
The cyclic compound in which the ring
forming atom is only carbon are called
homocyclic or carbocyclic compounds. For
example,
benzene cyclopentane

26. (i) Alicyclic compounds
The cyclic organic compounds which are similar to
open chain compound in chemical behaviour are
called alicyclic or cyclic aliphatic compounds. For
example,
cyclopropane cyclobutane cyclopentane
(ii) Aromatic compounds
The cyclic organic compound which consist of at least
one benzene ring and alternate carbon to carbon
single and double bond having (4n+2) number of π
electron system are called aromatic compounds. For
example,

27. benzene phenol aniline
(b) Heterocyclic organic compounds
The cyclic organic compound in which the ring
forming atom are carbon and one or more hetero
atoms (O, N, S, X etc) are called heterocyclic organic
compounds. For example, epoxyethane, THF, pyrrole,
pyridine etc.

28. (i) Aliphatic heterocyclic compounds
The heterocyclic compound which are similar to aliphatic
compound on their behaviour are called aliphatic
heterocyclic compound. For example,
epoxyethane tetrahydrofuran piperidine pyrrolidine
(ii) Aromatic heterocyclic compounds
The heterocyclic compound which are similar to aromatic
compound on their behaviour are called aromatic
heterocyclic compound. For example,
pyrrole pyridine furan thiophene

29. Functional group
An atom or group of atoms that determines the
chemical properties (nature or behaviour) of organic
compound is called functional group. For example, -
X, -OH, -CHO, -COOH, -NH₂, -NO₂ etc.
Generally organic compound are formed by combining
two parts i.e. functional group and molecular body. The
molecular body is only hydrocarbon part that determines
physical property and functional group is reactive site that
determines chemical property.
R G (R-OH, R-X)
Hydrocarbon part Functional group
(Molecular body) (Reactive site)
Physical property Chemical property

30. S.N. Class of Organic
compounds
Functional
Name
Groups
Symbol
1. Alkenes alkene -C=C-
2. Alkynes alkyne -C≡C-
3. Alkyl halides halo -X (X=F,Cl,Br,I)
4. Alcohols hydroxy -OH
5. Aldehydes formyl -CHO
6. Ketones oxo or keto >C=O
7. Carboxylic acids carboxyl -COOH
8. Amides amido -CONH₂
9. Esters ester -COO-
10. Acid halides acid halide -COX

31. S.N. Class of Organic
compounds
Functional
Name
Groups
Symbol
11. Acid anhydride acid anhydride -(CO)₂O
12. Ethers ether -O-
13. Sulphonic acids sulphonic acid -SO₃H
14. Diazo compounds diazo or azo -N=N-
15. Cyanides (nitriles) cyanide (nitrile) -CN
16. Isocyanides isocyanide -NC
17. Nitro compounds nitro -NO₂
18. Nitrites nitrite -ONO
19. Thioles thiol (mercapto) -SH
20. Amines amino -NH₂

32. Homologous series
The hydrocarbons and their derivatives are called
organic compounds. There are large number of
organic compounds with same functional group. Each
functional group consist of particular class of organic
compound with various members.
A regular series of organic compounds having
same functional group in the increasing order of their
molecular mass is called homologous series. The
respective members of particular series are called
homologue and the phenomenon which involves their
formation is called homology.

33. Two regular members are differ by a –CH₂ unit
and thus their molecular mass is differ by 14 amu.
There is regular change in physical properties of each
homologue. For example,
1. Homologous series of alkane (CnH2n+2)
Series Name
CH₄ methane
CH₃-CH₃ ethane
CH₃-CH₂-CH₃ propane
CH₃-CH₂-CH₂-CH₃ butane
CH₃-CH₂-CH₂-CH₂-CH₃ pentane

34. 2. Homologous series of alcohol (CnH2n+1 OH)
Series Name
CH₃-OH methanol
CH₃-CH₂-OH ethanol
CH₃-CH₂-CH₂-OH propanol
CH₃-CH₂-CH₂-CH₂-OH butanol
CH₃-CH₂-CH₂-CH₂-CH₂-OH pentanol
3. Homologous series of carboxylic acid (CnH2n+1
COOH)
Series Name
H-COOH methanoic acid
CH₃-COOH ethanoic acid
CH₃-CH₂-COOH propanoic acid
CH₃-CH₂-CH₂-COOH butanoic acid

35. Characteristics of homologous series
1. All members of homologous series consist of same
functional group.
2. Each homologue possess same chemical properties
but different physical properties.
3. Each homologue can be represented by same
general formula having similar structure.
4. Each homologue can be prepared by same general
method.
5. Two regular members of homologous series differ
by a –CH₂ unit i.e. 14 amu. molecular mass.
6. The physical properties of homologue shows regular
gradation with rise in molecular mass.
7. First member of homologous series shows some
different behaviour than rest of members.

36. Fractional distillation of crude oil
…

37. Cracking or pyrolysis
The process of decomposition of higher hydrocarbon
of petroleum fractions into lower hydrocarbons with low
boiling point on strong heating in presence or absence of
catalyst is called cracking or pyrolysis. This process involves
the breaking of C-C and C-H bond which results the
formation of lower hydrocarbons depend upon the
condition employed for it. For example,

38. Reforming or aromatization
The process of conversion of aliphatic and alicyclic
hydrocarbon into aromatic hydrocarbon on strong heating
in presence of suitable catalyst is called reforming or
aromatization. This process involves dehydration,
isomerisation and cyclization. For example,

39. Quality of gasoline (Octane number)
The term which is used to determine the quality
of fuel is known as octane number. The quality of fuel
which is used to indicate the anti-knocking property in
internal combustion engine of vehicles is called
octane number. For example,
Iso-octane has anti-knocking property = 100
n-heptane has anti- knocking property = 0
CH₃ CH₃
CH₃-CH-CH₂-C-CH₃ CH₃CH₂CH₂CH₂CH₂CH₂CH₃
CH₃
Iso-octane (octane no = 100) n-heptane (octane no = 0)

40. Generally a quality of fuel is determined by its
octane number value. For example, A fuel has
octane number 80 that means a fuel has same anti-
knocking property to that of 80% iso-octane and
20% n-heptane by volume.
A quality of fuel (octane number) of different
hydrocarbon is given as;
Straight chain alkanes < branched chain alkanes <
alkenes and alkynes < cycloalkanes < aromatic
hydrocarbons.

41. Gasoline additives (Anti-knocking agent)
The chemical compounds which are added to
gasoline (fuel oil) to improve its octane number are
called anti-knocking agent.
Tetra-ethyl lead (TEL) is the best known anti-
knocking agent which is added to gasoline that
converts straight chain hydrocarbon into branched
chain hydrocarbon and improves its octane number.
For example,
(C₂H₅)₄Pb ⟶ 4 °C₂H₅ + Pb°
Tetraethyl lead ethyl lead
(TEL) radical radical

42. .
C₂H₅
CH₃CH₂CH₂CH₂CH₃ + °C₂H₅ ⟶ CH₃CH₂CHCH₂CH₃
straight chain branched chain
(low octane no.) (high octane no.)
The lead free radical produced may damage an
engine thus it can be removed as,
Pb° + CH₂-CH₂ ⟶ CH₂=CH₂ + PbBr₂↑
Br Br (volatile)

43. Cetane number
The term which is used to determine the
quality of diesel fuel is known as cetane number.
The quality of diesel which is used to indicate the
ignition property in internal combustion - engine of
vehicles is called cetane number. For example,
Cetane (Hexadecane) has cetane number = 100
α- methyl naphthalene has cetane number = 0
CH₃-(CH₂)₁₄-CH₃
n- hexadecane α-methyl naphthalene
Cetane no. = 100 Cetane no. = 0

44. The cetane number of diesel is the percentage
of cetane by volume in a mixture of cetane and α-
methyl naphthalene, which has same ignition
properties. For example, A diesel with cetane
number 75 has same ignition properties as the
mixture of 75% cetane and 25% α-methyl
naphthalene
Cetane ignites too rapidly which is assigned
the cetane number of 100 while α-methyl
naphthalene ignites too slowly due to its extremely
poor ignition properties, which is assigned the
cetane number of 0.

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