Chapter 6 Isomers
If two compounds have the same molecular formulae (in other words, the same number and types of atoms) but the atoms are arranged differently, they are classed as isomers. Care has to be taken with this definition, however, as the two examples in Figure 6.1 are not isomers but the same molecule bent into a different shape because the mobility that the single bond allows it. In this example, the arrangement of atoms differs by their arrangement in space only.
Bear in mind that a single bond enables a molecule to rotate freely around it, so the apparent change in the shape in the molecule does not make it an isomer (compare this with the limited rotation around a double bond, see Figure 6.5).
There are several different types of isomer:
Structural Isomers
Chain isomerism
Chain isomers (Figure 6.2(i)) occur because functional groups can branch off from the main carbon backbone. The number of carbon and hydrogen atoms remains the same but the structures are very different.
