University Federico II
of Naples, Italy
European Chemistry
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Stereochemistry

Stereochemistry (from Greek, solid) refers to chemistry in three dimensions.

Every molecule is characterised by a molecular formula that indicates the number and the nature of atoms constituting the molecule, and by a structural formula that depends on how atoms are linked and on their relative spatial positions.

Examples of different atom arrangements

CO2
Carbon dioxide
linear
CH4
Methane
tetrahedral
H2O
Water
angular

The three-dimensional arrangement of atoms defines the shape of the molecule

The shape of molecules is very important because it is responsible for some significant properties. For instance, they may taste sweet or bitter, have a given kind of aroma, a pharmacological activity, be it therapeutic or toxic. Actually, these properties depend on the interaction between appropriate molecules with complementary shapes, as it is occurring in the case of puzzle pieces.

Molecules that have the same molecular formula but different atom arrangements are called isomers (from Greek, equal parts).

Isomers are different compounds, characterised by different physical and chemical properties.

There are two kinds of isomers: constitutional isomers and stereoisomers.