Zaitsev's rule

A rule for where the double bond tend to form in elimination reactions. Zaitsev's rule states that a double bond will form to create the most stable alkene, that is, the one where the carbon atoms that form the double bond hold the most substituents.

Look at the reaction below, and try to count the number of non-hydrogen side-groups on the carbon atoms that share the double bond.

Figure 1. Elimination reaction with 3 potential products. In this example, the product in the middle will be the major one according the Zaitsev's rule.