Hydro Carbons Part - 1

                                            Hydrocarbons

The first question which arises in our minds is “what is a hydrocarbon”.?

So guys, a hydrocarbon is an organic compound which contains both hydrogen as well as carbon not any other substance (compounds, elements, etc.).

Hydrocarbons are examples of group 14 hydrides. Hydrocarbons, from which one hydrogen atom has been removed, are functional groups called hydrocarbyls. Because carbon has 4 electrons in its outermost shell (and because each covalent bond requires a donation of 1 electron, per atom, to the bond) carbon has exactly four bonds to make, and is only stable if all 4 of these bonds are used.

Aromatic hydrocarbons (arenes), alkanes, cycloalkanes and alkyne-based compounds are different types of hydrocarbons.

Most hydrocarbons found on Earth naturally occur in crude oil, where decomposed organic matter provides an abundance of carbon and hydrogen which, when bonded, can catenate to form seemingly limitless chains.

As defined by IUPAC nomenclature of organic chemistry, the classifications for hydrocarbons are in following types:
IUPAC- International Union of Pure and Applied Chemistry.

1). Saturated Hydrocarbons

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_nH_2n+2. The most general form of saturated hydrocarbons is C_nH_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 characteristics 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

Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms. Those with double bond are called alkenes. Those with one double bond have the formula C_nH_2n (assuming non-cyclic structures). Those containing triple bonds are called alkyne. Those with one triple bond have the formula C_nH_2n−2.

3). Aromatic Hydrocarbons

Aromatic hydrocarbons, also known as arenes, are hydrocarbons that have at least one aromatic ring.

Reactions

There are three main types of reactions:

• Substitution reaction
• Addition reaction
• Combustion

Substitution reaction

Substitution reactions only occur in saturated hydrocarbons (single carbon–carbon bonds).

e.g. an alkane reacts with a chlorine molecule. One of the chlorine atoms displaces a hydrogen atom one by one. This forms hydrochloric acid as well as the hydrocarbon with one chlorine atom.

CH₄ + Cl₂ → CH₃Cl + HCl

CH₃Cl + Cl₂ → CH₂Cl₂ + HCl

CH₂Cl₂ + Cl₂ → CHCl₃ + HCl

CHCl₃ + Cl₂ → CCl₄ + HCl

Here, CH₄ is Methane and CCl4 is Pyrene (carbon tetrachloride).

Addition reaction

Addition reactions involve alkenes and alkynes. In this reaction a halogen molecule breaks the double or triple bond in the hydrocarbon and forms a bond.

Combustion reaction

When any hydrocarbon burns it gives out water (H₂O) in the form of vapours and carbon dioxide (CO₂) and releases energy in the form of heat.

The simplest hydrocarbon, methane, burns as follows:

CH₄ + 2 O₂ → 2 H₂O + CO₂ + energy

In inadequate supply of air, carbon monoxide (CO) gas and water vapour are formed:

2 CH₄ + 3 O₂ → 2 CO + 4 H₂O

Another example is the combustion of propane:

C₃H₈ + 5 O₂ → 4 H₂O + 3 CO₂ + energy

And finally, for any linear alkane of n carbon atoms,

C_nH_2n+2 + 3n + 1/2 O₂ → (n + 1) H₂O + n CO₂ + energy.

Burning of hydrocarbons is an example of an exothermic chemical reaction.

Hydrocarbons can also be burned with elemental fluorine, resulting in carbon tetrafluoride and hydrogen fluoride products.

Petroleum

Extracted hydrocarbons in a liquid form are referred to as petroleum (literally "rock oil") or mineral oil, whereas hydrocarbons in a gaseous form are referred to as natural gas. Petroleum and natural gas are found in the Earth's subsurface with the tools of petroleum geology and are a significant source of fuel and raw materials for the production of organic chemicals.

The extraction of liquid hydrocarbon fuel from sedimentary basins is integral to modern energy development. Hydrocarbons are mined from oil sands and oil shale, and potentially extracted from sedimentary methane hydrates. These reserves require distillation and upgrading to produce synthetic crude and petroleum.

Oil reserves in sedimentary rocks are the source of hydrocarbons for the energy, transport and petrochemical industries.

Economically important hydrocarbons include fossil fuels such as coal, petroleum and natural gas, and its derivatives such asplastics, paraffin, waxes, solvents and oils. Hydrocarbons – along with NO_x and sunlight – contribute to the formation of tropospheric ozone and greenhouse gases.