We'll find that we have to begin to think in three dimensions to understand some structural differences between very similar compounds. Let's begin by reminding ourselves of some of the ideas involved in the topic of isomerism. This was introduced in Section 3.2 of Brown. Each of these connection patterns represents a different compound. For example, the oxygen in ethanol is connected to a CH 3 CH 2 group and to a hydrogen while the oxygen in dimethyl ether is connected to two methyl groups.
Connectivity is the key difference here.
Second, and this is new, we can describe this connectivity quite nicely using just the usual two dimensions we can conveniently represent on paper, a chalkboard, or a computer monitor. There are many types of organic compounds for which this description is inadequate. For these compounds and many others we will need to use three dimensions in order to have an adequate description of the structure. Let's look at some familiar objects so as to get a sense of when we will need to think about three dimensions. Consider the way in which a sock differs from a glove.