Chemistry Notes: Organic Compounds & Hydrocarbon

The compounds of carbon and hydrogen or compounds of carbon and hydrogen with some elements like nitrogen, phosphorus, sulphur, etc. are called the organic compounds. In earlier time it is thought that organic compound cannot be prepared in the laboratory because they require the vital force which exists only in living organisms.

Some Important Point:

• Urea was the first organic compound prepared in the laboratory by Wholer from the inorganic compound i.e. ammonium cyanate.
• Acetic acid was the first organic compound synthesized from the elements.
• Functional group: It is an atom or group of atom responsible for the chemical properties of the molecule. –OH is an alcoholic group, –CHO, –O– is either group.
• Isomers are the compounds having the same molecular formula but different structures.

Hydrocarbons

These are compounds of only hydrogen and carbon. These can be classified into the three types

*Saturated hydrocarbons: Methane is the first member of this group. They are bonded by only a single bond. These are also called alkanes and paraffin and have general formula C_nH_2n+2 where n can have any value i.e. n=1, 2, 3…..

*Unsaturated hydrocarbons: These hydrocarbons contain at least one double bond or one triple bond. They are popularly known as alkenes for double bond and alkynes for a triple bond. The general formula is C_nH_2n for alkenes and C_nH_2n-2 for alkynes.

*Aromatic hydrocarbons: They have a ring structure with alternate double bonds, e.g. Benzene.

Important Hydrocarbons and their Uses

Methane:

• It is popularly known as marsh gas damp fire. Paddy field or rice agriculture is the biggest source of this gas. Its mixture with air is explosive in nature. It is colourless and odourless gas. Natural gas contains 90% methane and some parts of butane and propane etc.
•  Due to this explosion occur in the mines. Used in the preparation of Carbon Black, used in the tyre industry.

Bio-gas:

It is a mixture of gases produced during the decay of biomass in the absence of oxygen. The main constituent of the Biogas is Methane about 75%, carbon 25% and a small proportion of hydrogen and nitrogen, and hydrogen sulphide. It burns without producing the smoke.

Various Compounds of Hydrogen and Carbon:

• Ethane (C₂H₆): used as a fuel and in making some organic compounds.  Its hexachloro derivative is known as artificial camphor.
• Butane (C₄H₁₀): A Main constituent of LPG, used as fuel. As LPG doesn’t have any smell so to detect in case of leakage ethyl mercaptan is mixed with butane.
• Ethylene (CH₂=CH₂): Used for the preparation of the mustard gas. It is used as an anesthetic for the preservation and artificial ripening of green fruits and also used in the manufacture of the PVC.
• Acetylene: A colourless gas with a sweet smell. The sweet smell is due to the presence of the phosphine present in it as an impurity.
• Benzene (C₆H₆): It is an aromatic hydrocarbon. It was discovered by Faraday. Used for the destructive distillation of the whale oil, and also used as a solvent for the fats and resins. It is also used in dry-cleaning and as motor fuel with the name benzol.
• Toluene (C₆H₅CH₃): Obtained with the dry distillation of Tolu Balsam. Used in the manufacturing of the TNT explosive, drugs, dyestuffs and saccharin. Combination of petrol, benzene, and toluene is used as antifreeze.

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