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Hydrocarbons

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Hydrocarbons are the simple group of lipids because basically they contain only carbon and hydrogen atoms. In their linear or cyclic form the hydrocarbons of biological origin are very frequently substituted by oxygenated groups. All these chemical forms will be grouped under the heading hydrocarbons and distributed into several classes according to their linear or cyclic structure.

The large number of hydrocarbons in the troposphere implies that they can have major roles in air pollution chemistry.

Definition

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"Hydrocarbon is an organic compound containing atoms only of carbon and hydrogen." In order to study the compounds of hydrogen they are divided into two main groups.
  1. Aliphatic hydrocarbons
  2. Aromatic hydrocarbons
The classification of hydrocarbons is shown below with the help of the flowchart.

Hydrocarbons

Saturated

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Saturated hydrocarbons are those in which adjacent carbon atoms are joined by a single valence bond and all other valences are satisfied by hydrogen. The saturated hydrocarbons form a whole series of compounds starting with one carbon atom and increasing by one carbon atom. These compounds are also known as the paraffin series, the methane series and the alkanes.

Example - alkanes - carbon chains connected by single bonds and having the structural formula CnH2n+2.

Unsaturated

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An unsaturated hydrocarbon is a hydrocarbon in which one or more carbon-carbon multiple bonds are present. Unsaturated hydrocarbons have physical properties similar to saturated hydrocarbons. Unsaturated hydrocarbons are chemically more reactive than their saturated counterparts.The increased reactivity of unsaturated hydrocarbon is related to the presence of the carbon carbon multiple bonds. These multiple bonds serve as locations where chemical reactions can occur.

Unsaturated hydrocarbons are subdivided into three groups
  • Alkenes - which contain one or more carbon-carbon double bonds
  • Alkynes - which contain one or more carbon-carbon triple bonds
  • Aromatic hydrocarbons - which exhibit a special type of "delocalized" bonding that involves a six-membered carbon ring.

Aliphatic

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These include open chain compounds and cyclic compounds based on the skeleton of the carbon chain present, aliphatic hydrocarbons are categorized into two classes.
  1. Acyclic hydrocarbons (or) open chain hydrocarbons
  2. Alicyclic hydrocarbons (or) cycloalkanes
The classification of aliphatic hydrocarbons is shown below. 
Aliphatic Hydrocarbons

Aromatic

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Aromatic hydrocarbons are collectively known as arenes. They contain one or more hexagonal carbocyclic rings. The name aromatic is derived from the Greek word "aroma"meaning sweet smell because most of the compounds belonging to this class had sweet fragrance. One of the earliest aromatic hydrocarbons known is benzene.

Aromatic Hydrocarbon

Naming

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The following are the rules listed for naming the hydrocarbons.
  1. Find the longest continuous chain and name it as if it were an alkane (if it contains no multiple bonds between the carbon atoms).
  2. Name the side branches in the same manner.
  3. Identify the number of the carbon atoms in the longest chain to which the branch is attached by counting from the end of the chain nearest to the branch.
  4. If it is possible that there could be any confusion as to which carbon atom is meant put the number in front of the name of the compound, followed by a dash.
  5. If there is more than one branch, use the numbers to identify the carbon atom to which they are attached.
  6. If the branches are identical use the prefixes di for two, tri for three, tetra for four and so on.
The naming of hydrocarbons using the IUPAC system is shown below with an example.

IUPAC for Hydrocarbons

Derivatives

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Hydrocarbon derivative is comprised of one or more hydrocarbon radicals attached to a functional group. A functional group is essentially another compound although it too is electrically unbalanced and must be bonded to something else. The examples below illustrate two different alcohols created by joining the same functional group of different hydrocarbon radicals.

Hydrocarbon Derivative

Sources

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All fossil fuels (coal, oil, gas) are basically hydrocarbons, deviating however significantly in their H:C ratio.

H:C ratio of natural hydrocarbon sources is tabulated below.

Methane 4.0
Natural gas 3.8
Petroleum crude 1.8
Tar sand bitumen 1.5
Shale oil (raw) 1.5
Bituminus coal 0.8

Properties

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The general properties of hydrocarbons are tabulated below.

Typical appearence Liquids and gases are clear and colorless. Most solids are white or transparent (compounds with many double bonds can be brightly colored.
Typical density (Liquids and solids) 0.6 to 0.9g/ml
(Most hydrocarbons float on top of water)
State at room temperature 1 to 4 carbon atom : gas.
More than 5 carbon atoms : liquid or solid.
Compounds with more than 15 carbon atoms are usually solids but the cutoffs quite variable the shape of the molecules plays an important role in determining the melting point)
Solubility in water Very low: hydrocarbons are considered to be insoluble in water.

Examples

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Some of the examples of hydrocarbons are
  1. Ethane
  2. Butane
  3. Hexane
  4. Octane
  5. Methane
  6. Heptane
  7. Propane
  8. Benzene
  9. Napthalene etc.