This document discusses different types of hydrocarbons. It begins by classifying hydrocarbons into four general classes: alkanes, alkenes, alkynes, and arenes. It then provides details on the structure, properties, methods of preparation, and isomerism of alkanes, alkenes, and alkynes. It notes that alkanes are saturated and contain single carbon-carbon bonds, while alkenes contain carbon-carbon double bonds and alkynes contain carbon-carbon triple bonds. The document also discusses aromatic hydrocarbons and notes that many contain benzene rings. It provides information on the nomenclature and isomerism of different hydrocarbons.

1. HYDROCARBON
S
V I S H A L S A H U
X I - B
4 3
P P T

2. CLASSIFICATION
• Hydrocarbons are organic compounds that
contain only carbon and hydrogen. The four
general classes of hydrocarbons are: alkanes,
alkenes, alkynes and arenes. Aromatic compounds
derive their names from the fact that many of these
compounds in the early days of discovery were
grouped because they were oils with fragrant
odors.

3. ALKANES
Alkanes are saturated,
open chain hydrocarbons
containing carbon-carbon
single bonds. e.g., methane
(CH4), ethane (C4H6)
propane (C3H8), etc.
Alkanes exhibit chain
isomensm, position
isomerism and
conformational isomerism
These hydrocarbons are
inert under normal
conditions [i.e.,do not react
with acids. bases and other
reagents).

4. METHODS OF
PREPERATION
OF ALKANES • Preparation of Alkanes from unsaturated hydrocarbon:
• Alkane can be prepared from alkene and alkyne through the process of
hydrogenation. In this process, dihydrogen gas is added to alkynes and
alkenes in the present catalyst. This catalysts which are finely divided is like
nickel, palladium or platinum to form alkanes. With the help of nickel as the
catalyst, this reaction takes place at an elevated temperature, whereas the
reaction takes place at room temperature with platinum as the catalyst.

5. METHODS
OF
PREPERATIO
N
OF ALKANES
• Preparation of Alkanes from alkyl halides:
• Alkane can be produced from alkyl halides predominantly by
two ways:
• Alkanes can be prepared from alkyl halides (except fluorides)
through reduction with zinc and dilute hydrochloric acid.
• CH3-Cl + H2 → CH4 + HCl
• 2. Wurtz reaction: In dry ethereal solution, on treating alkyl
halides with sodium metal, production of alkanes is higher. By
this reaction, we can achieve higher alkanes with an even
number of carbon atoms.
• CH3-Br + 2Na + BrCH3 → CH3-CH3 + 2NaBr

6. METHODS OF PREPERATION OF ALKANES
• Preparation of alkanes from carboxylic acids:
• Preparation of alkanes from carboxylic acids mainly happens via two means:
Alkanes can be prepared from carboxylic acid via the removal of carbon dioxide.
This process is known as decarboxylation. It produces alkane with a carbon atom
lesser than that present in the carboxylic acid.
2. Kolbe’s electrolytic method: In this process, the alkane is produced through electrolysis
of sodium or potassium salt of carboxylic acid.

7. ISOMERISM
• In n-alkanes, no carbon is bonded to more than two other carbons, giving rise to a
linear chain. When a carbon is bonded to more than two other carbons, a branch
is formed. The smallest branched alkane is isobutane. Notice that isobutane has
the same molecular formula, C4H10, as n-butane but has a different structural
formula. Two different molecules which have the same molecular formula are
isomers. Isomers which differ in the connectivity of bonds are constitutional
isomers, or structural isomers. Isobutane is a constitutional isomer of n-butane.
The prefix "iso" indicates that branches off of the central carbon are equivalent.

8. • n-butane and isobutane are the only constitutional isomers of C4H10.
Pentane, C5H12, has three while hexane, C6H14, has five.

9. NOMENCLATURE
• Isobutane, neopentane, etc. are trivial names that arise from common
usage. As you can see, the number of isomers increases rapidly for
larger alkanes. It would be impractical to give trivial names to every
isomer. What is needed is a systematic, easy-to-use method of naming
that works for even the most complex of molecules. Such a name should
unambiguously identify the structural formula of the named molecule.
This system is IUPAC nomenclature, devised by the International Union
of Pure and Applied ChemistsThe IUPAC system considers molecules in
terms of a parent hydrocarbon chain with substituents attached to it. The
parent is the longest continuous carbon chain in the compound, and the
base name of the compound is the alkane that corresponds to the parent
chain. Then, consecutively number the carbons of the parent chain in
such a way that the substituents are attached to carbons with lower
numbers. The name of the compound is the parent alkane prefixed by its
substituents and their position numberings

10. • The -CH3 group is called a methyl group. In
general, alkyl substituents are derived from the
corresponding alkanes by replacing the -ane suffix
with -yl. These substituents are used so frequently
that they are given abbreviated names. For
instance, methyl groups can be abbreviated as -
Me. In some instances, the exact nature of the
substituent is unimportant. In such cases the
notation -R can be used to denote a radical group,
a general substituent that can be any organic
component

11. ALKENES
• Alkenes are a class of hydrocarbons (e.g,
containing only carbon and hydrogen)
unsaturated compounds with at least one
carbon-to-carbon double bond. Another term
used to describe alkenes is olefins. Alkenes are
more reactive than alkanes due to the presence
of the double bond.
• Alkenes are acyclic (branched or unbranched)
hydrocarbons having one carbon-to-carbon
double bond (C=C) and the general molecular
formula CnH2n [16]
• alkenes contain less than the maximum possible
number of hydrogen atoms per carbon atom,
they are said to be unsaturated.

12. METHODS OF
PREPERATIONS OF
ALKENES
• From alkynes: Alkynes can be used for the preparation of
alkenes. Alkyne to alkene conversion is carried out by the
reduction of alkynes with hydrogen in the presence of
palladised charcoal. The charcoal used is moderately
deactivated with the help of quinoline or sulphur
compounds. This reaction results in the formation of
alkenes. Palladised charcoal which is halfway deactivated
is called as Lindlar’s catalyst. The alkenes obtained from
the above reaction have cis geometry. In order to form
trans alkenes, alkynes are made to undergo reduction with
sodium in liquid ammonia.

13. • From alkyl halides: Alkenes are obtained by
heating alkyl halides with alcoholic potash. Alcoholic
potash is obtained by dissolving potassium
hydroxide in alcohol. In this reaction,
dehydrohalogenation takes place i.e. a single
molecule of halogen acid is removed. The rate of
reaction depends upon the alkyl group and the
nature of the halogen group attached.

14. • From vicinal halides: Vicinal dihalides can be defined as the dihalides in which
two adjacent carbon atoms are attached to two halogens. When such dihalides
react with zinc metal, they lose halogen molecules which result in the formation of
alkenes. Such a reaction of preparation of alkenes from Vicinal dihalides is known
as dehalogenation.

15. • From alcohols: Alcohols reacts with
concentrated sulphuric acid which results in
the formation of alkenes due to the
elimination of a water molecule. As water
molecule is removed in this reaction, it is
called as acidic dehydration of alcohol and
the dehydrating agent is concentrated
sulphuric acid.

16. ISOMERISM
• Isomerism of alkene
• Alkenes have two types of geometrical isomers :
1. Cis isomer: The isomers which are formed by cis isomerism is called as cis
isomers.
2. Trans isomer: The isomers which are formed by trans isomerism is called as
trans isomers.
• Alkenes due to the presence of double bond, shows geometrical and structural
isomerism.
• Properties of geometrical isomers of alkene
• 1. Melting Point : In general , the melting point of trans-isomers is higher than
that of the cis-isomers.
2.Solubility : In general , the solubility of a cis-isomers is higher than that of the
trans-isomers.
3.Dipole moment : Cis-isomers of an alkene is found to be more polar than the
trans-isomers mostly.
4.Boiling point : The boiling point of the cis-isomers are higher than those of
the trans-isomers in general.
• .

17. ALKYNES
• The alkynes are unsaturated hydrocarbons that contain one triple bond,
the general formula of alkynes CnH2n+2 and the triple bond is known as
the ‘acetylenic bond’. Many alkynes have been found in nature. Ethyne
(C2H2) is the first member of the alkyne family, with two carbon atoms
connected by a triple bond.
• In organic chemistry, an alkyne is an unsaturated hydrocarbon
containing at least one carbon-carbon triple bond. Like
other hydrocarbons, alkynes are generally hydrophobic. Ethyne is more
commonly known under the trivial name acetylene. It is the simplest of
the alkynes, consisting of two carbon atoms connected by a triple bond,
leaving each carbon able to bond to one hydrogen atom.

18. METHODS OF
PREPERATION
S OF ALKYNES • Dehydrohalogenation of alkyl dihalides
• In this method of preparation, alkenes are made to react with a
halogen. Due to this reaction, a substituted alkane is
obtained. Alkanes formed are further passed through alcoholic KOH in
order to form substituted alkenes. It is then made to react with sodium
amide to form alkynes. This process is called dehydrohalogenation as
hydrogen is eliminated along with a halogen in order to obtain an
alkyne.

19. • Preparation of acetylene from calcium
carbide
• For large scale production of an
alkyne, calcium carbide (CaC2) is made to
react with water. It is prepared by heating
quicklime in the presence of coke. Quicklime
is obtained by introducing limestone to heat.
The reactions for the preparation of acetylene
from calcium carbide are as shown below:
• CaCO3 → CaO + CO2
• CaO + 3C → CaC2 + CO
• CaC2 + 2H2O → Ca (OH)2 + C2H2

20. • Preparation from vicinal dihalides
• Dihalides are obtained from corresponding alkenes by
the addition of halogens (Group 17 elements). Alkynes
are obtained from vicinal dihalides by
dehydrohalogenation which is carried out in two steps:
• The first step is to prepare the unsaturated halides. The
halides formed have a halogen attached to a double-
bonded carbon. These halides are called vinylic halides
which are not reactive in nature. These halides are made
to react with the strong base which results in the
formation of alkynes. Metal acetylides are used to
convert small alkynes into large ones.

21. ISOMERISM AND
NOMEMCLATURE
• isomerism of alkynes
• Alkynes shows structural isomerism in which positional isomerism is common.
Example: Pent-1-yne and Pent-2-yne are positional isomers.
Nomenclature of alkynes
• In common name system, alkynes are named as derivatives of acetylene. In
IUPAC, they are named as derivatives of the corresponding alkanes replacing
ane by the suffix yne.
• Classification of alkynes according to the triple bond
• According to the position of triple bond alkynes are classified as di-yne if two
triple bond is present, tri-yne if three triple bond is there and so on.

22. AROMATIC
HYDROCARBONS
• The aromatic hydrocarbons are “unsaturated hydrocarbons which
have one or more planar six-carbon rings called benzene rings, to
which hydrogen atoms are attached”. Many aromatic hydrocarbons
contain a benzene ring (also referred to as an aromatic ring).
The benzene ring is stabilized by resonance and the pi electrons are
delocalized in the ring structure.
• A few examples of aromatic hydrocarbons are provided below. It can be
observed that all these compounds contain a benzene ring.
•

23. NOMENCLATURE AND
ISOMERISM
• • We have already discussed about nomenclature of
aromatic hydrocarbons in Unit:11. The first member
of aromatic hydrocarbon is benzene (C6H6)
represented by a regular hexagon with a circle
inscribed in it.
• • Since, all the six hydrogen atom in benzene are
equivalent, it can give only one mono-substituted
compound (Ex) methyl benzene (C6H5-CH3) which
named as toluene.

24. • • When di substitution occurs either by a similar
monovalent atom or two different atoms or groups
in benzene, then three different position isomers
are possible. Their relative positions are indicated
as ortho (1,2), meta (1,3) and para (1,4). For
example, consider dimethyl benzene which is
named as xylene.