Cis-trans isomers are a type of geometric isomerism found in certain compounds, particularly those with double bonds or ring structures. In cis isomers, similar or identical groups are positioned on the same side of the double bond or ring, while in trans isomers, these groups are on opposite sides. This arrangement can significantly affect the physical and chemical properties of the compounds. Cis-trans isomerism is commonly observed in organic molecules, such as alkenes and cycloalkanes. For example, in 2-butene, the cis isomer has both methyl groups on the same side, whereas the trans isomer has them on opposite sides. These differences can influence boiling points, solubility, and reactivity.