Hydrocarbon

Hossain Uchsas> Departmet of Pharmacy,NSTU //hossainuchsas4057@yahoo.com 1
Hydrocarbon
Hydrocarbon, any of a class of organic
chemical compounds composed only of the
elements carbon (C) and hydrogen (H). The
carbon atoms join together to form the
framework of the compound, and the
hydrogen atoms attach to them in many
different configurations. Ex- petroleum,
natural gas & raw materials of
plastics, fibres, rubbers, solvents, explosives,
and industrial chemicals.
Aliphatic Hydrocarbons
Alkanes, hydrocarbons in which all the bonds
are single. C—C and C—H bond is a sigma
(σ) bond (see chemical bonding).
One compound, called n-butane, where the
prefix n- represents normal, has its four
carbon atoms bonded in a continuous chain.
The other, called isobutane, has a branched
chain.
Number of possible alkane isomers
molecular formula number of constitutional isomers
C3H8 1
C4H10 2
C5H12 3
C6H14 5
C7H16 9
C8H18 18
C9H20 35
C10H22 75

molecular formula number of constitutional isomers
C15H32 4,347
C20H42 366,319
C30H62 4,111,846,763
IUPAC names of unbranched alkanes
alkane formula name alkane formula name
CH4 methane CH3(CH2)6CH3 octane
CH3CH3 ethane CH3(CH2)7CH3 nonane
CH3CH2CH3 propane CH3(CH2)8CH3 decane
CH3CH2CH2CH3 butane CH3(CH2)13CH3 pentadecane
CH3(CH2)3CH3 pentane CH3(CH2)18CH3 icosane
CH3(CH2)4CH3 hexane CH3(CH2)28CH3 triacontane
CH3(CH2)5CH3 heptane CH3(CH2)98CH3 hectane
Three-dimensional structures
the shape of a regular tetrahedron
with carbon at the centre and
a hydrogen atom at each corner. Each
H―C―H angle in methane is 109.5°, and
each C―H bond distance is 1.09 angstroms
(Å; 1Å = 1 × 10−10
metre). Higher alkanes
such as butane have bonds that are
tetrahedrally disposed on each carbon except
that the resulting C―C―C and H―C―H
angles are slightly larger and smaller,
respectively, than the ideal value of 109.5°
characteristic of a perfectly symmetrical
tetrahedron. Carbon-carbon bond distances in
alkanes are normally close to 1.53 angstroms
.

Aromatic Hydrocarbons
benzoic acid (C6H5CO2H)
Benzene (C6H6)
toluene (C6H5CH3)
Two groups that contain benzene rings,
C6H5―(phenyl) and C6H5CH2―(benzyl),
have special names, as in these examples:

name
boiling
point (°C)
melting
point (°C)
benzene 80.1 +5.5
toluene 110.6 −95
ethylbenzene 136.2 −94
p-xylene 138.4 +13
styrene 145 −30.6
naphthalene 218 +80.3
anthracene 342 +218
phenanthrene 340 +100
Physical constants of benzene and selected
arenes
Cycloalkanes
Organic compounds are connected in a chain,
closes to form a ring. Saturated hydrocarbons
that contain one ring are referred to as
cycloalkanes. With a general formula of
CnH2n (n is an integer greater than 2).
whereas cyclohexane (C6H12) is the most
studied, best understood, and most important.
In naming cycloalkanes, alkyl groups
attached to the ring are indicated explicitly

and listed in alphabetical order.
Stereoisomerism
Physical properties
Alkanes and cycloalkanes
are nonpolar substances. Attractive forces
between alkane molecules are dictated by
London forces (or dispersion forces, arising
from electron fluctuations in
molecules; see chemical bonding:
Intermolecular forces) and are weak. Thus,
alkanes have relatively low boiling
points compared with polar molecules of
comparable molecular weight. The boiling
points of alkanes increase with increasing
number of carbons. This is because the
intermolecular attractive forces, although
individually weak, become cumulatively
more significant as the number of atoms
and electrons in the molecule increases.
name formula
boili
ng
point
(°C)
meltin
g
point
(°C)
methane CH4 −164
−182.
5

name formula
boili
ng
point
(°C)
meltin
g
point
(°C)
ethane CH3CH3
−88.
6
−183.
3
propane
CH3CH2CH
3
−42
−189.
7
butane
CH3(CH2)2
CH3
−0.5
−138.
35
pentane
CH3(CH2)3
CH3
+36.
1
−129.
7
hexane
CH3(CH2)4
CH3
+68.
9
−95.0
heptane
CH3(CH2)5
CH3
+98.
4
−90.6
octane
CH3(CH2)6
CH3
+125
.6
−56.8
nonane
CH3(CH2)7
CH3
+150
.8
−51.0
decane
CH3(CH2)8
CH3
+174
.1
−29.7
pentadeca
ne
CH3(CH2)13
CH3
+270 +10
octadecan
e
CH3(CH2)16
CH3
+316
.1
+28.2
icosane
CH3(CH2)18
CH3
+343 +36.8
triacontan
e
CH3(CH2)28
CH3
+449
.7
+65.8
tetraconta
ne
CH3(CH2)38
CH3
— +81
name formula
boili
ng
point
(°C)
meltin
g
point
(°C)
pentacont
ane
CH3(CH2)48
CH3
— +92
Physical properties of unbranched alkanes
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For a given number of carbon atoms,
an unbranched alkane has a higher boiling
point than any of its branched-chain isomers.
This effect is evident upon comparing the
boiling points (bp) of selected C8H18 isomers.
An unbranched alkane has a more extended
shape, thereby increasing the number of
intermolecular attractive forces that must be
broken in order to go from the liquid state to
the gaseous state. On the other hand, the
relatively compact ellipsoidal shape of
2,2,3,3-tetramethylbutane permits it to pack
into a crystal lattice more effectively than
octane and so raises its melting point(mp).
In general, solid alkanes do not often have
high melting points. Unbranched alkanes
tend toward a maximum in that the melting
point of CH3(CH2)98CH3 (115 °C [239 °F]) is
not much different from that of
CH3(CH2)148CH3 (123 °C [253 °F]).
The viscosity of liquid alkanes increases with
the number of carbons. Increased
intermolecular attractive forces, as well as an
increase in the extent to which nearby
molecules become entangled when they have

an extended shape, cause unbranched alkanes
to be more viscous than their branched-chain
isomers.
The densities of liquid hydrocarbons are all
less than that of water, which is quite polar
and possesses strong intermolecular
attractive forces. All hydrocarbons are
insoluble in water and, being less dense than
water, float on its surface. Hydrocarbons are,
however, usually soluble in one another as
well as in organic solvents such as diethyl
ether (CH3CH2OCH2CH3).
Sources and occurrence
The most abundant sources of alkanes
are natural gas and petroleum deposits,
formed over a period of millions of years by
the decay of organic matter in the absence
of oxygen. Natural gas contains 60–80
percent methane, 5–9 percent ethane, 3–18
percent propane, and 2–14 percent higher
hydrocarbons. Petroleum is a complex liquid
mixture of hundreds of substances—
including 150 or more hydrocarbons,
approximately half of which are saturated.
Approximately two billion tons of methane
are produced annually by the bacteria that
live in termites and in the digestive systems
of plant-eating animals. Smaller quantities of
alkanes also can be found in a variety of
natural materials. The so-called aggregation
pheromone whereby Blaberus
craniifer cockroaches attract others of the
same species is a 1:1 mixture of the volatile
but relatively high-boiling liquid alkanes
undecane, CH3(CH2)9CH3, and tetradecane,
CH3(CH2)12CH3. Hentriacontane,
CH3(CH2)29CH3, is a solid alkane present to
the extent of 8–9 percent in beeswax, where
its stability and impermeability to water
contribute to the role it plays as a structural
component.
With the exception of the alkanes that are
readily available from petroleum, alkanes are
synthesized in the laboratory and in industry
by the hydrogenation of alkenes. Only a few
methods are available in which a carbon-
carbon bond-forming operation gives an
alkane directly, and these tend to be suitable
only for syntheses carried out on a small
scale.
Chemical reactions
i)
ii) aluminum chloride (AlCl3) catalyst
iii) UV Light
iv) Dehydrogenation of ethane
v) Alkenes and alkynes

Alkenes (also called olefins) and alkynes
(also called acetylenes) belong to the class of
unsaturated aliphatic hydrocarbons.
vi)
vii) Dehydration of alcohols
viii) Dehydrohalogenation (loss of a
hydrogen atom and a halogen atom) of alkyl
halides.
ix)
x)
xi)
xii)
Polymerization (xiii-xviii)
xiii)

xiv)
xv)
xvi)
xvii)
xviii)
xix) Hydrolysis
xx)

xxi)
xxii) Ozonolysis reaction
xxiii)alkylation
xxiv) Acylation

Hydrocarbon

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Hydrocarbon