Hydro carbons
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Hydrocarbons
Hydrocarbons, in organic chemistry, family of
organic compounds, composed entirely of carbon and
hydrogen. They are the organic compounds of simplest
composition and may be considered theoretically as the
parent substances from which all other organic
compounds are derived. The hydrocarbons are
conveniently classified into two major groups, openchain and cyclic. In open-chain compounds containing
more than one carbon atom, the carbon atoms are
attached to each other to form an open chain; the chain
may carry one or more side branches. In cyclic
compounds the carbon atoms form one or more closed
rings. The two major groups are subdivided according to
chemical behaviour into saturated and unsaturated
compounds.
THE ALKANE SERIES
GENERAL FORMULA :
CnH2n
The saturated open-chain hydrocarbons form a homologous series
called the alkane, or paraffin, series. The composition of each of the
members of the series corresponds to the formula CnH2n +2, where
n is the number of carbon atoms in the molecule. Among the
members of the series are methane, CH4; ethane, C2H6; propane,
C3H8; and butane, C4H10. All the members of the series are
unreactive; that is, they do not react readily at ordinary temperatures
with such reagents as acids, alkalis, or oxidizers. The first four
members of the series are gases at ordinary temperature and
pressure; intermediate members are liquids; and the heavier
members are semi-solids or solids. Petroleum contains a great
variety of saturated hydrocarbons, and such petroleum products as
petrol, heavy fuel oil, lubricating oils, petroleum jelly, and paraffin
consist principally of mixtures of paraffin hydrocarbons, which range
from the lighter liquid members to the solid members.
THE ALKYNE SERIES
The members of the alkyne series contain a
triple bond between two carbon atoms in
the molecule. They are very active
chemically and are not found free in
nature. They form a series analogous to
the alkene series. The first and most
important member of the series is ethyne,
C2H2.
CYCLIC HYDROCARBONS



The simplest of the saturated cyclic hydrocarbons, or cycloalkanes, is
cyclopropane, C3H6, the molecules of which are made up of three carbon
atoms to each of which two hydrogen atoms are attached. Cyclopropane is
somewhat more reactive than the corresponding open-chain alkane,
propane, C3H8. Other cycloalkanes make up a part of ordinary petrol.
Several unsaturated cyclic hydrocarbons, having the general formula
C10H16, occur in certain fragrant natural oils that are distilled from plant
materials. These hydrocarbons are called terpenes and include pinene (in
turpentine) and limonene (in lemon and orange oils).
The most important group of unsaturated cyclic hydrocarbons is the
aromatics, which occur in coal tar. Although the aromatics sometimes
exhibit unsaturation—that is, the addition of other substances—their
principal reactions bring about the replacement, or substitution, of hydrogen
atoms by other kinds of atoms or groups of atoms. The aromatic
hydrocarbons include benzene, toluene, anthracene, and naphthalene
Ethylene:
Structure of ethylene
Properties of Ethane (ethylene)
•colorless
gas
at
room
temperature
and
pressure
Melting point -169oC, Boiling point -104oC
•slightly sweet smell
•flammable
•non-polar molecule: soluble in non-polar solvents & insoluble in
polar solvents like water
reactive:
the
active
site
is
the
double
bond
Readily
undergoes
addition
reactions,
for
example
reacts with bromine water (red-brown) to produce colorless 1,2dibromoethane
CH2=CH2(g) + Br2(l) -----> CH2Br-CH2Br(g)
Reactions of Ethene (ethylene)
Addition of Bromine
CH2=CH2 + Br2
----->
CH2BrCH2Br
1,2-dibromoethane
Addition of Chlorine
CH2=CH2 + Cl2
AlCl3
----->
CH2ClCH2Cl
1,2-dichloroethane
Addition of Hydrogen bromide
CH2=CH2 + HBr
AlCl3
----->
CH3CH2Br
bromoethane
Addition of Hydrogen chloride
CH2=CH2 + HCl
AlCl3
----->
CH3CH2Cl
chlorooethane
Addition of Hydrogen
CH2=CH2 + H2
Ni
----->
500oC
CH3CH3
ethane
Addition of Water
CH2=CH2 + H2O
H3PO4
----->
300oC
CH3CH2OH
ethanol
Combustion
CH2=CH2 + 3O2
excess air
----->
2CO2 + 2H2O
Reaction of hydro carbon
•acetylene
•Bert helot
•carbon
•catalyst
•fuel cell
•hydrogenation
•smog
•Ziegler
Bertha lot :
French chemist. The first professor of organic chemistry at the College de
France (from 1865), he later also held high government offices, incl. that of
foreign minister (1895-96). He did research in alcohols and carboxylic acids, the
synthesis of hydrocarbons, and reaction rates, studied the mechanism of
explosion, discovered many coal-tar derivatives, and wrote on the history of
early chemistry. He was a pioneer in the use of chemical analysis as a tool of
archaeology.
fuel cell :
Device that converts chemical energy of a fuel directly into electricity (see
electrochemistry). Fuel cells are intrinsically more efficient than most other
energy-conversion devices. Electrolytic chemical reactions cause electrons to
be released on one electrode and flow through an external circuit to a second
electrode. Whereas in batteries the electrodes are the source of the active
ingredients, which are altered and depleted during the reaction, in fuel cells the
gas or liquid fuel (often hydrogen, methyl alcohol, hydrazine, or a simple
hydrocarbon) is supplied continuously to one electrode and oxygen or air to the
other from an external source. So, as long as fuel and oxidant are supplied, the
fuel cell will not run down or require recharging
hydrogenation :
Chemical reaction between molecular hydrogen (H2) and another element or a
compound, usually in the presence of a catalyst. It may involve adding
hydrogen at the sites of double or triple bonds (see bonding) to make them
single bonds (i.e., to saturate an unsaturated compound; see saturation), or to
aromatic compounds to make them cyclic hydrocarbons.