If two molecules are mirror are images of one another but not superimposable, they are referred to as being enantiomers of one another. Enantiomers are chiral molecules that have the same formula and the same connectivity, but their arrangement in three dimensions is different. Enantiomers have the opposite chirality, or “handedness.”
A familiar example of this is the relationship between a right hand and a left hand. They both have four fingers and a thumb, both are mirror images of each other, but a right hand will not fit into a left glove.
Examples of Chiral molecules with their enantiomers:
D-Lactic acid is a by-product of anaerobic exercise, where as its enantiomer L Lactic acid is not normally found.
Limonene is a member of a class of molecules called terpenes. There are two stereoisomers of limonene: the D version smells like oranges an is commonly used as a flavoring agent. L Limonene is much less common, and because of the different stereochemistry it has a piney, terpentine like odor.