Cis-2-butene and trans-2-butene are geometric isomers of the alkene 2-butene C4H8 . They have the same molecular formula but differ in the spatial arrangement of their atoms around the double bond. The structural differences between these two isomers arise from the restricted rotation around the carbon-carbon double bond C=C due to the presence of a pi bond. This results in two distinct configurations: cis and trans.In cis-2-butene, the two methyl groups CH3 are on the same side of the double bond, while in trans-2-butene, the two methyl groups are on opposite sides of the double bond. This difference in spatial arrangement leads to different physical and chemical properties for the two isomers.When reacting with hydrogen gas H2 in the presence of a catalyst such as palladium or platinum , both cis-2-butene and trans-2-butene undergo an addition reaction called hydrogenation. The double bond C=C is broken, and a hydrogen atom is added to each of the carbon atoms involved in the double bond, resulting in the formation of an alkane.Cis-2-butene + H2 Butane C4H10 Trans-2-butene + H2 Butane C4H10 Although both isomers produce the same product butane in this reaction, they may exhibit different reaction rates due to their structural differences. The cis isomer has both methyl groups on the same side of the double bond, causing more steric hindrance crowding around the double bond. This makes it more difficult for the hydrogen molecules to approach and react with the double bond. On the other hand, the trans isomer has the methyl groups on opposite sides of the double bond, resulting in less steric hindrance and easier access for the hydrogen molecules to react with the double bond.As a result, the hydrogenation reaction of trans-2-butene is generally faster than that of cis-2-butene due to the lower steric hindrance in the trans isomer.