Zaitsev's Rule can be used to predict the regiochemistry of elimination reactions.
Zaitsev’s or Saytzev’s (anglicized spelling) rule is an empirical rule used to predict regioselectivity of 1,2-elimination reactions occurring via the E1 or E2 mechanisms. It states that in a regioselective E1 or E2 reaction the major product is the more stable alkene, (i.e., the alkene with the more highly substituted double bond). For example:
E1 reaction always follow Zaitsev’s rule; with E2 reactions, there are exceptions (see antiperiplanar).