Eliminations 2: The E1, E1cb, E2, and Ei Mechanisms
The elimination of an electrofuge, Efg, and a nucleofuge, Nfg, from adjacent atoms to form alkenes can proceed via several subtly different mechanisms. The mechanism will likely have an effect upon the cis-trans isomer distribution of the products.,

For more information look in the Chemogenesis webbook sections on fragmentation reactions and elimination reactions.