The name is the same irrespective of how the molecule is represented
The image at the right represents a molecule containing four carbon atoms (black) in a chain and a one carbon branch. The hydrogens (grey spheres) attached to each carbon are also shown. It would be very difficult to use such a complicated picture every time we wanted to represent the structure of an organic molecule; thus we use condensed formulae such as those shown below. It is important to recognize that a variety of condensed formulae may represent the same molecule. For example all of the condensed formulae below are different ways of representing the four-carbon molecule shown above.
(1)
(2)
(CH3)2CHCH2CH3 CH3CH2CH(CH3)2
(3)
- The molecule above looks like the condensed structure (1). Place your mouse over the molecule to see that structure (2) is also a valid representation.
- This molecule can also be represented by (3). Roll your mouse over condensed structure (3) to see how it is related to condensed structures (1) and (2).
- It is safest to draw the branches in the chains as has been done in (1), (2) and (3). However, because the two CH3 groups at the left end of structure (1) and the right end of structure (2) are equivalent; they can be written in brackets with a subscript as in the bottom two formulae.
One way to test whether two representations are indeed different molecules is to name the compound. The name is characteristic of the structure and does not depend on its representation.