text: The regioselectivity of water elimination is highly influenced by ring size. When water is eliminated from cyclic tertiary alcohols by an E1 route, three major products are formed. The semicyclic isomer (so-called because the double bond is shared by a ring atom and an exocyclic atom) and the (E) endocyclic isomer are expected to predominate; the (Z) endocyclic isomer is not expected to be formed until the ring size is large enough to accommodate the awkward angles of the trans configuration. The exact population of each product relative to the others differs considerably depending upon the size of the ring involved. As the ring size increases, the semicyclic isomer decreases rapidly and the (E) endocyclic isomer increases, but after a certain point, the semicyclic isomer begins to increase again. This can be attributed to transannular strain; this strain is significantly reduced in the (E) endocyclic isomer because it has one less substituent in the ring than the semicyclic isomer.