encis-zeatin encis-heterozygote encis-2-butylene encis-2-butene encis-2,6-dimethylmorpholine entrans-cis isomers encis double bond enisosafrol (cis + trans) encis-trans test encis-4,4'-dinitrostilbene enfatty acids with cis-cis methylene interrupted double bonds encis-2-butenedoic acid