Organic Chemistry

What is Organic Chemistry?

Organic chemistry is in all aspects of our lives:

• our clothes
• food
• cosmetics

The common factor is that these products are based on the element carbon. The simplest organic compounds, hydrocarbons, contain only carbon and hydrogen.

Carbon can form many compounds as a carbon atom:

• Can form bonds with other carbon atoms to make chains and rings.
• Can form single, double and triple bonds with other carbon atoms.
• Can also bond with other atoms e.g. oxygen, nitrogen and hydrogen.

Functional Groups

This is a group of atoms in a compound responsible for the chemical properties. Molecules with the same functional group react in a similar way.

Homologous Series

• Contain the same functional group
• Have similar chemical properties
• Have same general formula: e.g. for alkanes: $C_{n}H_{2n+2}$

Saturated and Unsaturated Hydrocarbons

A saturated hydrocarbon is a compound with only single bonds. Unsaturated compounds contain at least one carbon-carbon multiple bond.

Aliphatic and Allicyclic Hydrocarbons

• Aliphatic hydrocarbons are joined together in straight or branched chains.
• Alicyclic hydrocarbons are joined together in a ring structure.

Alkanes

Alkanes are saturated hydrocarbons containing only $C-C$ bonds. For alkanes each carbon atom is bonded to four other atoms.

The first ten alkanes are as follows:

• $CH_{4}$ - Methane
• $C_{2}H_{6}$ - Ethane
• $C_{3}H_{8}$ - Propane
• $C_{4}H_{10}$ - Butane
• $C_{5}H_{12}$ - Pentane
• $C_{6}H_{14}$ - Hexane

Empirical Formula

This is the simplest whole number ratio of atoms of each element present in a compound.

Worked Example

A hydrocarbon was found to contain 85.68% carbon and 14.37% hydrogen. Calculate its empirical formula.

100g of the compound contains 85.68g of C and 14.37g of H.
Find the molar ratio:

$C: \frac {85.68} {12} = 7.14 \kern 3ex H: \frac {14.37} {1} = 14.37$

Divide by the smallest:

$C: \frac {7.14} {7.14} = 1 \kern 3ex H: \frac {14.37} {7.14} = 2$

$CH_{2}$