Strereoisomerism

Remember that structural isomers have the same molecular formula but different structural formulas. Stereoisomers have the same molecular formula and structural formula, but their atoms are arranged differently in space. There are two types of stereo isomers:

• Geometrical isomers - Cis and trans forms due to the fact that the double bond can't rotate and also occurs in cyclic alkanes. Note, that the physical properties and chemical properties can be similar, but there will be difference in M.P's and B.P's and sometimes there are big differences. There can be chemical differences as well e.g. cis and trans but-2-ene-1,4-dioc acid.
• Optical isomerism- This is where there is a chiral carbon (asymmetrical) basically that means that there are four different groups attached to a carbon. They have the same physical properties apart from the direction with which they rotate the plane of polarized light. However, when they react with optically active compounds there can be marked and dramatic differences. For example the thalidomide drug, which unfortunately was taken by many in the 60's to combat morning sickness in pregnancy.

The following are some chem guide links on optical isomerism:

Plane polarised light

Optical isomerism