Introduction to Organic Chemistry: Hydrocarbons, Functional Groups, and Polymers

Hydrocarbons

Hydrocarbons are compounds composed solely of carbon and hydrogen atoms. They serve as the basis for organic chemistry and can be classified into two main categories:

• Alkanes (saturated hydrocarbons): These straight-chain or branched molecules contain only single bonds between carbon atoms. They have the general formula CnH2n+2.
• Alkenes (unsaturated hydrocarbons): These molecules contain at least one carbon-carbon double bond. They have the general formula CnH2n.

Crude Oil and Fractional Distillation

Crude oil, formed by the decomposition of ancient marine organisms, is the primary source of hydrocarbons. Through fractional distillation, a process that separates the components based on their boiling points, various fractions of crude oil are obtained, including:

• Refinery gases (e.g., methane, ethane)
• Petrol (gasoline)
• Kerosene
• Diesel oil
• Lubricating oils
• Bitumen (used for road surfacing)

Alkanes

Alkanes are saturated hydrocarbons that exhibit relatively low reactivity due to their stable single bonds. They are commonly used as fuels and lubricants. The properties of alkanes include:

• Increasing boiling and melting points with increasing molecular mass
• Insoluble in water but soluble in non-polar solvents
• Complete combustion, producing carbon dioxide and water

Alkenes and Polymerization

Alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond. They undergo addition reactions, such as:

• Addition of bromine water: Bromine water is used as a test for unsaturation. Alkenes decolorize bromine water due to the addition of bromine molecules across the double bond.
• Polymerization: Alkenes can undergo addition polymerization, where monomers (individual molecules) join together to form long-chain polymers. This process is essential in the production of various plastics.

Worked Example: Polymerization

Ethene (C2H4) monomers can polymerize to form polyethene (polythene):

n C2H4 → (-CH2-CH2-)n

Polyethene is a widely used plastic with applications in packaging, pipes, and insulation.

Functional Groups

In addition to hydrocarbons, organic chemistry explores compounds containing functional groups, which influence the chemical properties and reactivity of the molecule. Two important functional groups are:

1. Alcohols: Containing the -OH group, alcohols can be produced by the addition of water to alkenes. They are used as solvents and in the production of alcoholic beverages.
2. Carboxylic acids: With the -COOH group, carboxylic acids exhibit acidic properties and can react with bases to form salts. Examples include acetic acid (vinegar) and fatty acids (found in fats and oils).