Explain what is meant by optical isomerism.

Stereoisomers are molecules that have the same structural formula, but a different arrangement of the atoms in space.Optical isomers are a type of stereoisomers where the two molecules have non-superimposable mirror images.This means that you couldn't slide one molecule exactly over the other because something would always be pointing in the wrong direction. Like putting your hands over each other. There is no way that if you can rotate them so that they align with each other, and look exactly the same. Stereoisomers arise when the central carbon atom is joined to 4 different groups. E.g. 2 hydoxypropanoic acid (draw it).When there are 4 different groups attached, there is no symmetry anywhere in the molecule. A molecule which has no plane of symmetry is described as chiral. And the central carbon which causes this lack of symmetry is called the chiral centre (and is usually labelled with a little star). A molecule with a plane of symmetry is described as achiral.Only chiral molecules have optical isomers. The two isomers are known as enantiomers.Enantiomers have different effects on plane polarised light, hence why it is optical isomerism. A solution of one enatiomer rotates the plane of polarised light in a clockwise direction, and a solution of the other enatiomer rotates the plane of polarisation in an anticlockwise direction.