Isomers

 Isomers are basically two or more compounds that have the same molecular structure, but are different in their structural formulas and have differernt chemical properties. An example of an isomer would be butane and isobutane.

There are two main types of isomerism: structural isomerism and stereoisomerism. Structural isomerism includes chain, position and functional group isomerism, whereas stereoisomerism refers to geometric isomerism and optical isomerism.

The number of structural isomers possible in organic chemistry increases dramatically in relation to increasing the length of the carbon chain, for example decane (containing 10 carbons) has 75 structural isomers, whereas a chain consisting of 40 carbon atoms will have 62,000,000,000 structural isomers. Position isomers and functional group isomers refer to the position of the functional group on the carbon chain and also the type of functional group  present in the molecule. Chain isomerism, as one may expect, denotes changes to the structure of the carbon chain.

Geometric isomerism is also referred to as cis-trans or E-Z isomerism. It relies on the restricted rotation of the carbon-carbon double bond, as different isomers arise from the positions of similar or dissimilar groups on the carbons attached by the double bond. Optical isomerism, requires a chiral carbon to be bonded to 4 different groups in a molecule. Optical isomers are non-superimposable on one another and are often referred to as right hand and left hand enantiomers.