CHAPTER HYDROCARBONS
Definition: Those organic compounds which contain carbon (C) and hydrogen (H) only are
called “Hydrocarbons”. For example, methane (CH4), ethane (CH3CH3), propane
(CH3CH2CH3) and butane (CH3CH2CH2CH3) etc.
Types of hydrocarbons
Hydrocarbons can be classified into the following categories.
A. Aliphatic hydrocarbons B. Aromatic hydrocarbons
Definition: Those hydrocarbons (HC) which contain open chain are called “aliphatic
hydrocarbons”. Aliphatic hydrocarbons can be further classified into the following categories.
i. Open chain/acyclic hydrocarbons ii. Straight chain hydrocarbons iii.
branched chain hydrocarbons iv. Saturated hydrocarbons v.
unsaturated hydrocarbons vi. Closed chain/cyclic hydrocarbons
i. Open chain/acyclic hydrocarbons
Definition: Those hydrocarbons which contain aliphatic chain or open chain are called “open
chain/acyclic hydrocarbons”. These may be straight chain or branched chain hydrocarbons.
ii. Straight chain hydrocarbons
Definition: Those hydrocarbons in which carbon atoms form only linear or straight chain are
called “straight chain hydrocarbons”. For example,
, H H H H H H
H C H H C C H H C C C H
H H H H H H
methane ethane propane
H H H H H H H H
H C C C C H H C C C C H
H H H H H H H H
butane butane
iii. Branched chain hydrocarbons
Definition: Those hydrocarbons in which carbon atoms form a branch in a chain are called
“branched chain hydrocarbons”. Both straight chain and branched chain hydrocarbons can be
saturated and unsaturated hydrocarbons. Examples of branched chain hydrocarbons are;
H CH3 H H CH3 CH3 H
H C C C H H C C C C H
3 2 1 4 3 2 1
H CH3 H H CH3 CH3 H
2,2-dimethylpropane 2,2,3,3-tetramethylbutane
iv. Saturated hydrocarbons
Definition: Those hydrocarbons in which carbon atoms form a single bond with other carbon
atoms having carbon atoms fully satisfied and carbon atoms form four single covalent bonds
are called “saturated hydrocarbons”. For example,
H H H H H H
H C H H C C H H C C C H
H H H H H H
methane ethane propane
v. Unsaturated hydrocarbons
,Definition: Those hydrocarbons in which carbon atoms form double or triple bond with other
carbon atoms are called “Unsaturated hydrocarbons”. For example,
H2C CH2 HC CH
ethene acetylene
vi. Closed chain/cyclic hydrocarbons
Definition: Those hydrocarbons in which carbon atoms form a cyclic chain or ring having
aliphatic character are called “closed chain/cyclic hydrocarbons”. They are also called
“cycloalkanes”. Cycloalkanes can be saturated or unsaturated. For example,
CH2
CH2 H2C CH2 H2C CH2
H2C CH2 H2C CH2 CH2 CH2
cyclopropane cyclobutane cyclopentane
Saturated hydrocarbons (cycloalkanes)
Unsaturated hydrocarbons (cycloalkenes/cycloalkynes) are given below;
CH2
CH
C CH2
CH2 H2C CH2 HC CH2
C CH2
HC CH HC CH CH2 CH2 CH2
cyclopropene cyclobutene cyclopentene cyclohexyne
Alkanes
Definition: Open chain saturated hydrocarbons in which carbon atoms form an open chain or
linear chain (saturated chain) are called “alkanes”. Alkanes having general formula CnH2n+2 (n
is the number of carbon atom). For example, methane, ethane, propane, butane and pentane
etc.
, Cycloalkanes
Definition: Closed chain saturated hydrocarbons in which carbon atoms form a closed or
cyclic chain are called “cycloalkanes”. Cycloalkanes having general formula CnH2n (n is the
number of carbon atoms & n≥3). For example, cyclopropane, cyclobutane and cyclopentane
etc.
Nomenclature of alkanes
The systematic process of naming a compound is called “nomenclature”.
At the beginning of Organic Chemistry, each new compound was given an individual name
which was based on its source. For example, formic acid (HCOOH) was given the name
formic acid because it was obtained from red ants. Thus
Those names which are based on the basis of source are called “common names” or trivial
names”.
With the increase in the number of organic compounds, it became impossible to give
common names to such large number of organic compounds. Therefore, it felt that names
must be given on the basis of structures. So “IUPAC” International Union of Pure and
Applied Chemistry in 1957 set rules to give systematic names to organic compounds on the
basis of structures which are called “IUPAC names” or “IUPAC” system of nomenclature.
There are two systems of nomenclature.
a. Common system
b. IUPAC system
a. Common system
Following are 10 alkanes from C1 to C10 having common names, formulas.
Definition: Those organic compounds which contain carbon (C) and hydrogen (H) only are
called “Hydrocarbons”. For example, methane (CH4), ethane (CH3CH3), propane
(CH3CH2CH3) and butane (CH3CH2CH2CH3) etc.
Types of hydrocarbons
Hydrocarbons can be classified into the following categories.
A. Aliphatic hydrocarbons B. Aromatic hydrocarbons
Definition: Those hydrocarbons (HC) which contain open chain are called “aliphatic
hydrocarbons”. Aliphatic hydrocarbons can be further classified into the following categories.
i. Open chain/acyclic hydrocarbons ii. Straight chain hydrocarbons iii.
branched chain hydrocarbons iv. Saturated hydrocarbons v.
unsaturated hydrocarbons vi. Closed chain/cyclic hydrocarbons
i. Open chain/acyclic hydrocarbons
Definition: Those hydrocarbons which contain aliphatic chain or open chain are called “open
chain/acyclic hydrocarbons”. These may be straight chain or branched chain hydrocarbons.
ii. Straight chain hydrocarbons
Definition: Those hydrocarbons in which carbon atoms form only linear or straight chain are
called “straight chain hydrocarbons”. For example,
, H H H H H H
H C H H C C H H C C C H
H H H H H H
methane ethane propane
H H H H H H H H
H C C C C H H C C C C H
H H H H H H H H
butane butane
iii. Branched chain hydrocarbons
Definition: Those hydrocarbons in which carbon atoms form a branch in a chain are called
“branched chain hydrocarbons”. Both straight chain and branched chain hydrocarbons can be
saturated and unsaturated hydrocarbons. Examples of branched chain hydrocarbons are;
H CH3 H H CH3 CH3 H
H C C C H H C C C C H
3 2 1 4 3 2 1
H CH3 H H CH3 CH3 H
2,2-dimethylpropane 2,2,3,3-tetramethylbutane
iv. Saturated hydrocarbons
Definition: Those hydrocarbons in which carbon atoms form a single bond with other carbon
atoms having carbon atoms fully satisfied and carbon atoms form four single covalent bonds
are called “saturated hydrocarbons”. For example,
H H H H H H
H C H H C C H H C C C H
H H H H H H
methane ethane propane
v. Unsaturated hydrocarbons
,Definition: Those hydrocarbons in which carbon atoms form double or triple bond with other
carbon atoms are called “Unsaturated hydrocarbons”. For example,
H2C CH2 HC CH
ethene acetylene
vi. Closed chain/cyclic hydrocarbons
Definition: Those hydrocarbons in which carbon atoms form a cyclic chain or ring having
aliphatic character are called “closed chain/cyclic hydrocarbons”. They are also called
“cycloalkanes”. Cycloalkanes can be saturated or unsaturated. For example,
CH2
CH2 H2C CH2 H2C CH2
H2C CH2 H2C CH2 CH2 CH2
cyclopropane cyclobutane cyclopentane
Saturated hydrocarbons (cycloalkanes)
Unsaturated hydrocarbons (cycloalkenes/cycloalkynes) are given below;
CH2
CH
C CH2
CH2 H2C CH2 HC CH2
C CH2
HC CH HC CH CH2 CH2 CH2
cyclopropene cyclobutene cyclopentene cyclohexyne
Alkanes
Definition: Open chain saturated hydrocarbons in which carbon atoms form an open chain or
linear chain (saturated chain) are called “alkanes”. Alkanes having general formula CnH2n+2 (n
is the number of carbon atom). For example, methane, ethane, propane, butane and pentane
etc.
, Cycloalkanes
Definition: Closed chain saturated hydrocarbons in which carbon atoms form a closed or
cyclic chain are called “cycloalkanes”. Cycloalkanes having general formula CnH2n (n is the
number of carbon atoms & n≥3). For example, cyclopropane, cyclobutane and cyclopentane
etc.
Nomenclature of alkanes
The systematic process of naming a compound is called “nomenclature”.
At the beginning of Organic Chemistry, each new compound was given an individual name
which was based on its source. For example, formic acid (HCOOH) was given the name
formic acid because it was obtained from red ants. Thus
Those names which are based on the basis of source are called “common names” or trivial
names”.
With the increase in the number of organic compounds, it became impossible to give
common names to such large number of organic compounds. Therefore, it felt that names
must be given on the basis of structures. So “IUPAC” International Union of Pure and
Applied Chemistry in 1957 set rules to give systematic names to organic compounds on the
basis of structures which are called “IUPAC names” or “IUPAC” system of nomenclature.
There are two systems of nomenclature.
a. Common system
b. IUPAC system
a. Common system
Following are 10 alkanes from C1 to C10 having common names, formulas.
