In 2-butene, the isomer with both methyl groups on the same side of the C=C double bond is called the:

1. Geometric isomers of alkenes are named according to whether similar groups sit on the same side or opposite sides of the double bond. 2. The text states: "The 2-butene isomer in which the two methyl groups are on the same side is called a cis-isomer the one in which the two methyl groups are on opposite sides is called a trans-isomer." 3. "Meso" and "racemic" describe unrelated concepts (internal symmetry and mixtures of enantiomers), not cis/trans alkene geometry. 4. So the same-side arrangement is specifically the cis-isomer. _Source: OpenStax Chemistry Ch 20 "Organic Chemistry", p.1105 §20.1 Hydrocarbons_