Alkenes Cis-trans isomers are not mirror images, so these are diastereomers. H CH3 c-c CC=C H3 H cis-2-bute ne trans-2-bute ne H、 8-0n 0- & OH C-C C=0 HO-C H H H fumaric acid,mp 287 C maleic acid,mp 138C essential metabolite toxic irritant Alkenes Cis-trans isomers are not mirror images, so these are diastereomers. C C H H H3 C CH3 cis-2-butene trans-2-butene C C H H3 C CH3 H HO C O C H C H C O OH fumaric acid, mp 287 C essential metabolite o H C C C H C O OH O HO maleic acid, mp 138 C toxic irritant o