1.1 Isomerism, isomers
1.1 Isomerism, isomers
A compound, whether it is organic or inorganic, always has its specific molecular formula. Reverse is, however, not always true. Thus a molecular formula can sometimes point out more than one compound. Molecules with the identical molecular formula and different structures are isomers, and such a phenomena is called isomerism.
The isomerism can be divided into some classes depending on how far those isomers are resembled each other. In order to understand the isomerism, it is necessary to determine and describe exactly the molecular structure of each molecule. The molecular formula provides the number and the type of atoms within a molecule.
It is a rational formula that specifies the group which the compound belongs to by showing functional units which are the source of the properties of a compound (functional group). Connecting one atom and another by required numbers of bonds lead to structural formula. It can completely describe molecular structures as far as the sequence of bonds is concerned.
It is not necessary to draw bonds corresponding to their actual lengths, even though bond lengths of C-C, C-O and C-H bonds in structural formula 2~5 are different each other. Actual bond angles between bonds are not also reflected in structural formula. For example, the real bond angle for <HOH of water H2O has been experimentally determined as about 104°. However, the structural formula of water is usually drawn as 6 or 7. Thus, the dimension and direction of bonds in structural formula may not precisely reflect the actual molecular structures.
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