We should also note that IUPAC changed their naming recommendations in 1993 to place the locant indicating the position of the double bond immediately before the -ene suffix rather than bofore the parent name: but-2-ene rather than 2-butene, for instance. This change has not been widely accepted by the chemical community, however, so we'll stay with the older but more commonly used names. Be aware, though, that you may occasionally encounter the newer system.