Hydrocarbons

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarbons. Hydrocarbons are generally colorless and hydrophobic with only weak odors.

1. Hydrocarbons
 
In organic chemistry, a hydrocarbon is an organic compound consisting 
entirely of hydrogen and carbon. ​Hydrocarbons ​are examples of group 
14 hydrides. Hydrocarbons from which one hydrogen atom has been 
removed are functional groups called ​hydrocarbons​. Hydrocarbons are 
generally colorless and hydrophobic with only weak odors. Because of 
their diverse molecular structures, it is difficult to generalize further. 

2. Types
As defined by IUPAC nomenclature of organic chemistry, the 
classifications for hydrocarbons are: 
1.Saturated hydrocarbons are the simplest of the hydrocarbon 
species. They are composed entirely of single bonds and are 
saturated with hydrogen. The formula for acyclic saturated 
hydrocarbons (i.e., alkanes) is C​
n​H​
2n+2​. The most general form 
of saturated ​hydrocarbons ​is C​
n​H​
2n+2(1-r)​, where r is the 
number of rings. Those with exactly one ring are the 
cycloalkanes. Saturated hydrocarbons are the basis of 
petroleum fuels and are found as either linear or branched 
species. Substitution reaction is their characteristic 
property (like chlorination reaction to form chloroform). 
Hydrocarbons with the same molecular formula but 
different structural formulae are called structural isomers. 
As given in the example of 3-methylhexane and its higher 
homologues, branched ​hydrocarbons ​can be chiral. Chiral 
saturated hydrocarbons constitute the side chains of 
biomolecules such as chlorophyll and tocopherol.
 
2.Unsaturated ​hydrocarbons ​have one or more double or 
triple bonds between carbon atoms. Those with double 
bonds are called alkenes. Those with one double bond have 
the formula C​
n​H​
2n​ (assuming non-cyclic structures). Those 
containing triple bonds are called alkyne. Those with one 
triple bond have the formula C​
n​H​
2n−2​.
 
3.Aromatic hydrocarbons, also known as arenes, are 
hydrocarbons ​that have at least one aromatic ring. 
Hydrocarbons can be gases (e.g. methane and propane), liquids (e.g. 
hexane and benzene), waxes or low melting solids (e.g. paraffin wax and 

3. naphthalene) or polymers (e.g. polyethylene, polypropylene and 
polystyrene). 
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The term 'aliphatic' refers to non-aromatic hydrocarbons. Saturated 
aliphatic hydrocarbons are sometimes referred to as 'paraffins'. 
Aliphatic hydrocarbons containing a double bond between carbon 
atoms are sometimes referred to as 'olefins'. 
 
Simple hydrocarbons and their variations
Num
ber 
of 
Alkane 
(single 
bond) 
Alkene 
(double 
bond) 
Alkyne ​(​triple 
bond) 
Cycloalk
ane 
Alkadiene 

4. carb
on 
ato
ms 
1 Methane  —  —  —  — 
2 Ethane Ethene 
(ethylene) 
Ethyne 
(acetylene) 
—  — 
3 Propane Propene 
(propylene) 
Propyne 
(methylacetyle
ne) 
Cyclopro
pane 
Propadiene 
(allene) 
4 Butane Butene 
(butylene) 
Butyne  Cyclobut
ane 
Butadiene 
5 Pentane Pentene  Pentyne  Cyclope
ntane 
Pentadiene 
(piperylene) 
6 Hexane Hexene  Hexyne  Cyclohe
xane 
Hexadiene 
7 Heptane Heptene  Heptyne Cyclohe
ptane 
Heptadiene 
8 Octane Octene  Octyne  Cyclooct
ane 
Octadiene 
9 Nonane Nonene  Nonyne  Cyclono
nane 
N​onadien​e 
10 Decane Decene  Decyne  Cyclode
cane 
Decadiene 

5. 11 Undecan
e 
Undecene Undecyne Cycloun
decane 
Undecadiene 
12 Dodecan
e 
Dodecene Dodecyne Cyclodo
decane 
Dodecadiene 
Usage
The predominant use of hydrocarbons is as a combustible fuel source. 
Methane is the predominant component of natural gas. The C​
6​
through 
C​
10​
alkanes, alkenes and isomeric cycloalkanes are the top components 
of gasoline, naphtha, jet fuel and specialized industrial solvent mixtures. 
With the progressive addition of carbon units, the simple non-ring 
structured hydrocarbons have higher viscosities, lubricating indices, 
boiling points, solidification temperatures, and deeper color. At the 
opposite extreme from methane lie the heavy tarts that remain as the 
lowest fraction in a crude oil refining retort. They are collected and 
widely utilized as roofing compounds, pavement composition 
(bitumen), wood preservatives (the creosote series) and as extremely 
high viscosity shear-resisting liquids. 
Some large-scale nonfuel applications of ​hydrocarbons ​begin with 
ethane and propane, which are obtained from petroleum and natural 
gas. These two gases are converted to ethylene and propylene. These 
two alkenes are precursors to polymers, including polyethylene, 
polystyrene, acrylates, polypropylene, etc. Another class of special 
hydrocarbons is BTX (chemistry), a mixture of benzene, toluene, and 

6. the three xylene isomers. Global consumption of benzene, estimated at 
more than 40,000,000 tons (2009). 
 
Hydrocarbons are also prevalent in nature. Some eusocial arthropods, 
such as the Brazilian stingless bee, Schwarziana quadripunctata, use 
unique hydrocarbon "scents" in order to determine kin from non-kin. 
The chemical hydrocarbon composition varies between age, sex, nest 
location, and hierarchal position.
 

7. Reactions
The noteworthy feature of hydrocarbons is their inertness, especially 
for saturated members. Otherwise, three main types of reactions can 
be identified: 
●Substitution reaction 
●Addition reaction 
●Combustion 
Free-radical reactions 
Substitution reactions only occur in saturated hydrocarbons (single 
carbon–carbon bonds). Such reactions require highly reactive reagents, 
such as chlorine and fluorine. In the case of chlorination, one of the 
chlorine atoms replaces a hydrogen atom. The reactions proceed via 
free-radical pathways. 
CH​
4​ + Cl​
2​ → CH​
3​Cl + HCl 
CH​
3​Cl + Cl​
2​ → CH​
2​Cl​
2​ + HCl 
all the way to CCl​
4​ (carbon tetrachloride) 
C​
2​H​
6​ + Cl​
2​ → C​
2​H​
5​Cl + HCl 
C​
2​H​
4​Cl​
2​ + Cl​
2​ → C​
2​H​
3​Cl​
3​ + HCl 
all the way to C​
2​Cl​
6​ (hexachloroethane) 
 
 

8. Substitution
 
Of the classes of hydrocarbons, aromatic compounds uniquely (or 
nearly so) undergo substitution reactions. The chemical process 
practiced on the largest scale is an example: the reaction of benzene 
and ethylene to give ethylbenzene. 
Addition reactions
Additional reactions apply to alkenes and alkynes. In this reaction a 
variety of reagents add "across" the pi-bond(s). Chlorine, hydrogen 
chloride, and hydrogen are illustrative reagents. Alkenes and some 
alkynes also undergo polymerization, alkene metathesis, and alkyne 
metathesis. 

9. Oxidation
Hydrocarbons are currently the main source of the world's electric 
energy and heat sources (such as home heating) because of the energy 
produced when they are combusted. Often this energy is used directly 
as heat such as in home heaters, which use either petroleum or natural 
gas. The hydrocarbon is burnt and the heat is used to heat water, which 
is then circulated. A similar principle is used to create electrical energy 
in power plants. 
Common properties of ​hydrocarbons ​are the facts that they produce 
steam, carbon dioxide and heat during combustion and that oxygen is 
required for combustion to take place. The simplest hydrocarbon, 
methane, burns as follows: 
CH​
4​ + 2 O​
2​ → 2 H​
2​O + CO​
2​ + energy 
In inadequate supply of air, carbon monoxide gas and water vapour are 
formed: 
2 CH​
4​ + 3 O​
2​ → 2 CO + 4 H​
2​O 
Another example is the combustion of propane: 
C​
3​H​
8​ + 5 O​
2​ → 4 H​
2​O + 3 CO​
2​ + energy 
And finally, for any linear alkane of n carbon atoms, 
C​
n​H​
2n+2​ +  
3n + 1 

10. / 
2 
O​
2​ → (n + 1) H​
2​O + n CO​
2​ + energy. 
Partial oxidation characterizes the reactions of alkenes and oxygen. 
This process is the basis of rancidification and paint drying. 
Origin
The vast majority of ​hydrocarbons ​found on Earth occur in petroleum, 
coal, and natural gas. Petroleum (literally "rock oil" – petrol for short) 
and coal are generally thought to be products of decomposition of 
organic matter. In contrast to petroleum, is coal, which is richer in 
carbon and poorer in hydrogen. Natural gas is the product of 
methanogenesis.
 
A seemingly limitless variety of compounds comprise petroleum, hence 
the necessity of refineries. These hydrocarbons consist of saturated 
hydrocarbons​, aromatic hydrocarbons, or combinations of the two. 
Missing in petroleum are alkenes and alkynes. Their production 
requires refineries. Petroleum-derived ​hydrocarbons ​are mainly 
consumed for fuel, but they are also the source of virtually all synthetic 
organic compounds, including plastics and pharmaceuticals. Natural 
gas is consumed almost exclusively as fuel. Coal is used as a fuel and as 
a reducing agent in metallurgy. 

11. Abiological Hydrocarbons 
 
A small fraction of hydrocarbon found on earth is thought to be 
abiological.
 
Some hydrocarbons also are widespread and abundant in the solar 
system. Lakes of liquid methane and ethane have been found on Titan, 
Saturn's largest moon, confirmed by the Cassini-Huygens Mission. 
Hydrocarbons are also abundant in nebulae forming polycyclic 
aromatic hydrocarbon (PAH) compounds.
 

12. Bioremediation
Bioremediation of ​hydrocarbons ​from soil or water contaminated is a 
formidable challenge because of the chemical inertness that 
characterize hydrocarbons (hence they survived millions of years in the 
source rock). Nonetheless, many strategies have been devised, 
bioremediation being prominent. The basic problem with 
bioremediation is the paucity of enzymes that act on them. Nonetheless 
the area has received regular attention. Bacteria in the gabbroic layer of 
the ocean's crust can degrade ​hydrocarbons​; but the extreme 
environment makes research difficult. Other bacteria such as 
Lutibacterium anuloederans can also degrade hydrocarbons. 
Mycoremediation or breaking down of hydrocarbon by mycelium and 
mushrooms is possible.
 
Safety
Hydrocarbons are generally of low toxicity, hence the widespread use 
of gasoline and related volatile products. Aromatic compounds such as 
benzene are narcotic and chronic toxins and are carcinogenic. Certain 
rare polycyclic aromatic compounds are carcinogenic. ​Hydrocarbons 
are highly flammable.