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Organic compounds include carbohydrates, proteins, lipids, enzymes, vitamins, drugs,
pharmaceutical products, fertilizers, pesticides, paints, dyes, synthetic rubbers, plastics,
artificial fibres and many polymers, etc.
11.1 ORGANIC COMPOUNDS
Today, there are about ten millions of organic compounds and thousands of new organic
compounds are being prepared every year. Therefore, the old definition has been rejected.
A detailed investigation of organic compounds revealed that all of them contain covalently
bonded carbon and hydrogen as their essential constituent. Hence, organic compounds are
hydrocarbons (compounds of carbon and hydrogen only ) and their derivatives, in which covalently
bonded carbon is an essential constituent. The branch of chemistry which deals with the study of
hydrocarbons and their derivatives is known as organic chemistry.
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Though, the oxides of carbon like carbon monoxide and carbon dioxide, carbonates,
bicarbonates and carbides are also carbon compounds, they are not treated as organic
compounds because their properties are quite different from those of organic compounds.
Each organic compound has specific formula.
There are four types of formulae of organic compounds:
• Molecular formula
• Structural formula
• Condensed formula
• Dot and cross formula
(i) Molecular Formula
The formula which represents the actual number of atoms in one molecule of the organic
compound is called the molecular formula, e.g., molecular formula of butane is C4H10. It shows:
a. Butane is made up of carbon and hydrogen atoms.
b. Each molecule of butane consists of 4 carbon atoms and 10 hydrogen atoms.
(ii) Structural Formula
Structural formula of a compound represents the exact arrangement of the different atoms
of various elements present in a molecule of a substance. In a structural formula, single
bond is represented by a single line (-), a double bond by two lines (=) and a triple bond by
three lines ( ) between the bonded atoms. Organic compounds may have same molecular
formulae but different structural formulae, e.g., structural formulae of butane C4H10 are:
(iii) Condensed Formula
The formula that indicates the group of atoms joined together to each carbon atom in a
straight chain or a branched chain is called the condensed formula.
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(iv) Electronic or Dot and Cross Formula
The formula which shows the sharing of electrons between various atoms in one molecule
of the organic compound is called dot and cross formula or electronic formula.
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Table 11.1: Names, Molecular, Condensed and Structural Formulae of the first ten
Hydrocarbons
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11.1.1 Classification of Organic Compounds
All known organic compounds have been broadly divided into two categories depending upon their
carbon skeleton. These are:
(i) Open chain or acyclic compounds.
(ii) Closed chain or cyclic compounds.
(i) Open chain or Acyclic compounds
Open chain compounds are those in which the end carbon atoms are not joined with each
other, in this way they form a long chain of carbon atoms. These chains may be either straight or
branched. For example,
(a) Straight chain compounds are those in which carbon atoms link with each other through a
single, double or triple bonds forming a straight chain such as;
(b) Branched chain compounds are those in which there is a branch along a straight
chain, such as:
Open chain compounds are also called aliphatic compounds.
(ii) Closed chain or Cyclic compounds
Closed chain or cyclic compounds are those in which the carbon atoms at the end of the
chain are not free. They are linked to form a ring. They are further divided into two classes:
(a) Homocyclic or carbocyclic compounds.
(b) Heterocyclic compounds.
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(a) Homocyclic or Carbocyclic compounds.
Homocyclic or carbocyclic compounds contain rings which are made up of only one kind
of atoms, i.e., carbon atoms. These are further divided into two classes:
• Aromatic compounds
• Alicyclic compounds
Aromatic compounds:
These organic compounds contain at least one benzene ring in their molecule. A benzene
ring is made up of six carbon atoms with three alternating double bonds. They are called
aromatic because of aroma or smell they have. For example:
They are also called benzenoid compounds.
Alicyclic or non-benzenoid compounds:
Carbocyclic compounds which do not have benzene ring in their molecules are called
alicyclic or non-benzenoid compounds. For example,
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(b) Heterocyclic compounds
Cyclic compounds that contain one or more atoms other than that of carbon atoms in their
rings are called heterocyclic compounds.
The classification may be summarized as follows:
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11.1.2 Diversity and Magnitude of Organic Compounds
There are a total of 118 elements known today. The number of organic compounds (carbon
compounds) is more than ten million. This number is far more than the number of compounds
of all the remaining elements taken together. The existence
of such a large number of organic compounds is due to the
following reasons:
(i) Catenation: The main reason for the existence of a
large number of organic compounds is that carbon atoms
can link with one another by means of covalent bonds to
form long chains or rings of carbon atoms. The chains can
be straight or branched. The ability of carbon atoms to link
with other carbon atoms to form long chains and large rings
is called catenation. Animation 11. 1: benzene
Source & Credit: campbell
Two basic conditions for an element to exhibit
catenation are:
1. Element should have valency two or greater than two.
2. Bonds made by an element with its own atoms should be stronger than the bonds made by the
element with other atoms especially oxygen.
Both silicon and carbon have similar electronic configurations but carbon shows catenation
whereas silicon does not. It is mainly due to the reason that C-C bonds are much stronger (355 kJ
mol-1) than Si-Si (200 kJ mol-) bonds. On the other hand, Si - O bonds are much stronger (452 kJ
mol-1) than C-O bonds (351 kJ mol-1). Hence, silicon occurs in the form of silica and silicates in nature.
(ii) Isomerism:
Another reason for the abundance of organic compounds is the phenomenon of isomerism.
The compounds are said to be isomers if they have the same molecular formula but different
arrangement of atoms in their molecules or different structural formulae.
Isomerism also adds to the possible number of structures, e.g., molecular formula C5H12 can be
represented by three different structures. Thus, C5H12 has three isomers, as shown below:
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Number of isomers increases with the increase in number of carbon atoms in the given
molecular formula.
(iii) Strength of covalent bonds of carbon: Due to its very small size, carbon can form
very strong covalent bonds with other carbon atoms, hydrogen, oxygen,nitrogen and
halogens. This enables it to form a large number of compounds.
(iv) Multiple bonding: In order to satisfy its tetravalency, carbon can make multiple bonds
(i.e., double and triple bonds). This further adds to the possible number of structures. For
example, two carbons in ethane are linked by a single covalent bond, by a double covalent
bond in ethylene and a triple covalent bond in acetylene.
11.1.3 General Characteristics of Organic Compounds:
Organic compounds have the following general characteristics:
(i) Origin: Naturally occurring organic compounds are obtained from plants and animals.
On the other hand, inorganic compounds are obtained from minerals and rocks.
(ii) Composition: Carbon is an essential constituent of all organic compounds. They are
made up of few elements such as carbon, hydrogen, nitrogen, oxygen, halogen, sulphur,
etc. On the other hand, inorganic compounds are made up of almost all the elements of
the Periodic Table known so far.
(iii) Covalent linkage: Organic compounds contain covalent bonds, that may be polar or
non-polar, while the inorganic compounds mostly contain ionic bonds.
(iv) Solubility:
Organic compounds having non-polar linkages are generally soluble in organic solvents like
alcohol, ether, benzene, carbon disulphide etc. On the other hand, the inorganic compounds
with ionic bonds are soluble in polar solvents like water.
(v) Electrical conductivity:
Due to the presence of covalent bonds, organic compounds are poor conductors of electricity,
whereas inorganic compounds being ionic in nature, are good conductors of electricity in
molten state or in aqueous solution.
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(vi) Melting and boiling points: Generally, organic compounds have low melting and boiling points
and are volatile in nature. Inorganic compounds, on the other hand, have comparatively high melting and
boiling points.
(vii) Stability: Since organic compounds have low melting and boiling points, they are less stable than
inorganic compounds.
(viii) Combustibility: Organic compounds with high percentage of carbon are generally combustible. On
the other hand, inorganic compounds are mostly non-combustible.
(ix) Isomerism: A main characteristic of organic compounds which differentiate them from inorganic
substances is their tendency to exhibit the phenomenon of isomerism. Isomerism is rare in inorganic
substance.
(x) Rate of reaction: Due to the presence of covalent linkages, the reactions of organic compounds are
molecular in nature. They are often slow and require specific conditions such as temperature, pressure or
catalyst.
1. Why and how carbon completes its octet?
2. Point out the properties of carbon which are responsible for
formation of long chains of carbon atom compounds.
3. Why are the melting and boiling points of organic compounds
low?
4. Why are the organic compounds poor conductors of electricity?
Test YourSelf 11.1 5. What are the reasons for the formation of millions of organic
compounds?
11.2 SOURCES OF ORGANIC COMPOUNDS
Organic compounds are prepared naturally by animals and plants. Animals synthesize two
main groups of organic compounds: proteins and fats. Proteins are meat, mutton, chicken
and eggs, etc. Fats are present in milk, butter, etc. Plants synthesize; carbohydrates, proteins,
fats, vitamins, etc
Moreover, dead plants buried under Earth’s crust are converted through biochemical processes
to coal, petroleum and gas. These materials are the main sources of organic compounds. We
can get thousands of organic compounds by the destructive distillation of coal and fractional
distillation of petroleum.
Details of each source are given in figure below:
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Fig. 11.1 Sources of organic compounds
11.2.1 Coal
Coal is a blackish, complex mixture of compounds of carbon, hydrogen and oxygen. It also
contains small amounts of nitrogen and sulphur compounds:
Coal was formed by the decomposition of dead plants buried under the Earth’s crust millions
of years ago. Conversion of wood into coal is called carbonization. It is a very slow biochemical
process. It takes place in the absence of air under high pressure and high temperature over
a long period of time (about 500 millions of years) as shown in figure 11.2. Wood contains
about 40% carbon, so depending upon the extent of carbonization process, four types of coal
are found. These types differ with respect to carbon content, volatile matter and moisture.
Table 11.2 shows the detail of contents of different types of coal and their uses in daily life
and industry.
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• Uses as Fuel: The fuels we use for automobiles and domestic purposes are coal, petroleum
and natural gas. These are called fossil fuels. All of these are organic compounds.
• Uses as Medicines: A large number of organic compounds (naturally synthesized by
plants) are used as medicines by us. Most of the life saving medicines and drugs such as
antibiotics (inhibit or kill microorganisms which cause infectious diseases) are synthesized
in laboratories.
• Uses as Raw Material: Organic compounds are used to prepare a variety of materials,
such as rubber, paper, ink, drugs, dyes, paints, varnishes, pesticides, etc.
1. Define petroleum.
2. What types of compounds are synthesized by plants?
3. What is the basic unit of carbohydrates and how is it synthesized?
4. CNG stands for ....
TestYourself 11.3
5. Our existence owes to organic compounds, comment.
11.4 ALKANES AND ALKYLRADICALS
Alkanes are saturated hydrocarbons or paraffins (para means little, affin means affinity).
Their general formula is C nH2n+2 , where ‘n’ is number of carbon atoms. In case of alkanes
‘n’ ranges from 1 to 40. In this way, alkanes form the most important homologous series of
compounds.
Homologous Series
Organic compounds are divided into groups of compounds having similar chemical properties.
Each group is known as a homologous series. Organic compounds of the same homologous
series have the following properties in common:
1. All members of a series can be represented by a general formula for example general
formulae of alkane, alkenes and alkynes are C nH2n+2 , CnH2n and CnH2n-2 , respectively.
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2. Successive members of the series differ by one unit of -CH2- and 14 units in their relative
molecular mass.
3. They have similar chemical properties (because they contain the same functional
group).
4. There is a regular change in their physical properties; the melting and boiling points
increase gradually with the increase of molecular masses.
5. They can be prepared by similar general methods.
Hydrocarbons are regarded as parent organic compounds. All other compounds are considered
to be derived from them by substituting one or more hydrogen atoms of a hydrocarbon by
one or more reactive atom or group of atoms.
Formation of Alkyl Radicals
Alkyl radicals are derivatives of alkanes. They are formed by the removal of one of the hydrogen
atoms of an alkane and are represented by a letter ‘R’. Their name is written by replacing
“ane” of alkane with ‘yl’ Table 11.3 represents first ten alkanes and their alkyl radicals. Their
general formula is CnH2n+1
Table 11.3 Names and Molecular Formulae of Alkanes and their Alkyl Radicals
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It is better to explain the type of radicals of propane and butane. Propane has a straight chain
structure. When terminal H is removed, it is called n-propyl. When hydrogen from central
carbon is removed, it is called isopropyl, as explained below:
Similarly, different structures of butyl radicals are explained:
11.5 FUNCTIONAL GROUPS
An atom or group of atoms or presence of double or triple bond which determines the characteristic
properties of an organic compound is known as the functional group. The remaining part of
the molecule mainly determines the physical properties such as melting point, boiling
point, density, etc. For example, -OH group is the functional group of alcohols, which gives
characteristics properties of alcohols. The characteristic properties of carboxylic acids are due
to the presence of -COOH group in them. Therefore, functional group of carboxylic acids is
-COOH group.
11.5.1 Functional Groups Containing Carbon, Hydrogen and Oxygen
The organic compounds containing carbon, hydrogen and oxygen as functional groups are
alcohols, ethers, aldehydes, ketones, carboxylic acids and esters. Their class name, functional
group, class formula and examples are given in the Table 11.4.
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(i) Alcoholic Group
The functional group of alcohol is -OH. Their general formula is ROH. Where R is any alkyl
group.
(ii) Ether Linkage
The functional group of ether is C - O - C. Their general formula is
R - O - R` where R and R’ are alkyl groups.
R and R’ may be same or different, such as:
H3C - O - CH3 Dimethyl ether, C2H5 - O - C2H5 , Diethyl ether
H3C - O - C2H5 , Ethyl methyl ether
(iii) Aldehydic Group
Aldehyde family consists of functional group.
Their general formula is RCHO.
Where R stands for H or some alkyl group, such as:
(iv) Ketonic Group
Compounds containing the functional group are called ketones.
They have the general formula where R and R’ are alkyl groups.
They may be same or different, such as:
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(v) Carboxyl Group
Compounds containing functional group are called carboxylic acids.
Their general formula is where R stands for — H or some alkyl group. Such as:
(vi) Ester Linkage
Organic compounds consisting of RCOOR’ functional group are called esters.
R and R’are alkyl groups. They may be same or
Their general formula is where
different, such as:
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Table 11.4 Functional groups containing carbon, hydrogen and oxygen
11.5.2 Functional Group Containing Carbon, Hydrogen and Nitrogen:
The organic compounds containing carbon, hydrogen and nitrogen as functional group
are called as amines. Their functional group is -NH2 and their general formula is R-NH2.
Examples of amines are:
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11.5.3 Functional Group Containing Carbon, Hydrogen and Halogens:
The organic compounds having functional group containing carbon, hydrogen and halogens
are called alkyl halides. Their functional group is R-X. ‘X’ may be F, CI, Br or I.
Table 11.5 Functional group containing carbon, hydrogen and halogens.
11.5.4 Double and Triple Bond:
Hydrocarbon consisting of double bonds between two carbon atoms in their molecules are
called as alkenes, such as:
Hydrocarbon consisting of triple bonds between two carbon atoms in their molecules are
called as alkynes, such as:
11.6 TESTS OF FUNCTIONAL GROUPS
11.6.1 Test for Unsaturation
(i) Bromine water test:
Dissolve a pinch of the given organic compound in 2.0 cm3 of carbon tetrachloride (CCI4).
Add 2 cm3 of bromine water in it and shake.
Result: Bromine will be decolourised.
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(ii) Baeyer’s test:
Dissolve about 0.2 g of the organic compound in water. Add to it 2-3 drops of alkaline
KMnO4 solution and shake.
Result: Pink colour will disappear.
11.6.2 Test for Alcoholic Group
(i) Sodium metal test:
Take about 2-3 cm3 of the given organic liquid in a dry test tube and add a piece of sodium
metal.
Result: Hydrogen gas will evolve.
(ii) Ester formation test:
Heat about 1.0 cm3 of the organic compound with 1.0 cm3 of acetic acid and 1-2 drops of
concentrated sulphuric acid.
Result: Fruity smell will be given out
11.6.3 Test for Carboxyl Group
(i) Litmus test:
Shake a pinch of the given compound with water and add a drop of blue litmus solution.
Result: Litmus solution will turn red.
(ii) NaHCO3 solution test:
Take about 2.0 cm3 of 5% NaHCO3 solution and add a pinch of given compound.
Result: CO2 gas with effervescence evolves.
11.6.4 Detection of Aldehydic Group
(i) Sodium bisulphite test:
Shake about 0.2 g or 0.5 cm3 of the given compound with 1-2 cm3 of saturated solution of
sodium bisulphite.
Result: A crystalline white precipitate will be formed.
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(ii) Fehling’s solution test:
Mix equal volumes of Fehling’s solution A and B in a test tube. Add a pinch of organic
compound and boil for five minutes.
Result: Red precipitate will be formed.
11.6.5 Test for Ketonic Group
(i) Phenyl hydrazine test:
Shake a pinch of the given organic compound with about 2.0 cm3 of phenyl hydrazine
solution.
Result: Orange red precipitate will be formed
(ii) Sodium nitroprusside test:
Take about 2.0 cm3 of sodium nitroprusside solution in a test tube and add 2-3 drops
of NaOH solution. Now add a pinch of the given compound and shake.
Result: Red colour will be formed.
(iii) With Fehling’s solution:
No reaction
11.6.6 Test for Primary Amino Group (-NH2)
(i) Carbyl amine test:
Heat about 0.2 g of the given compound and add 0.5 cm3 of chloroform and add 2-3 cm3 of
alcoholic KOH.
Result: Extremely unpleasant odour will be given out.
11.6.7 Test for Ester
They are recognized by their fruity smell.
i. What is the functional group of an ester?
ii. What is the difference between aldehydes and ketones?
iii. Give the functional groups of alkenes and alkynes.
iv. How is an alcohol tested?
Test Yourself 11.4 v. How is a ketonic group is tested?
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Pharmaceutical chemists work towards the partial and total
synthesis of effective drugs
Synthesis of effective drugs to control the epidemics and fatal
diseases is the need of the society. The responsibility to synthesize
effective drugs is of pharmaceutical chemists. They can evaluate the
efficiency and safety of these drugs. They make the drugs more and
more effective by reducing their side effects and enhancing potency.
Key Points
• Organic compounds are compounds of carbon and hydrogen and their derivatives.
• Compounds made up of carbon and hydrogen are called hydrocarbons. They are alkanes,
alkenes and alkynes.
• Organic compounds are molecular compounds having covalent bonding.
• They form homologous series of compounds, thus their properties resemble within a
series.
• Sources of organic compounds are animals, plants, coal, petroleum and natural gas.
• Dead plants buried under Earth’s crust are converted into coal; petroleum and gas. Coal
is blackish solid material.
• Coal is of four types, i.e peat, lignite, bituminous and anthracite.
• Destructive distillation of coal produces; coal gas, ammonical liquor; coal tar and coke.
• Petroleum is a dark brownish or greenish black coloured viscous liquid consisting of
several compounds. These compounds are separated by fractional distillation.
• Natural gas is a mixture of low molecular mass hydrocarbons. It is mainly used as fuel.
• Living plants synthesize macro-molecules (carbohydrates, proteins, fats and vitamins).
• Organic compounds can also be synthesized in laboratories ranging from the simplest
compounds to complex ones.
• Organic compounds have wide range of uses. They are used as food, clothing, housing
fuel, medicines and to prepare a variety of materials.
• Alkanes are saturated hydrocarbons, alkyl radicals are derivatives of alkanes which are
represented by ‘R’.
• An atom or a group of atoms that provide characteristic properties to an organic
compound is called functional group.
• Depending upon the functional groups, organic compounds are classified as alcohols,
ethers, aldehydes, ketones, carboxylic acids, esters, amines and alkyl halides.
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CONCEPT DIAGRAM
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