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How do cis-2-butene and trans-2-butene differ in the positions of their groups?

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Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — isomerism Tetrahedral geometry of methane: (A) stick-and-ball model and (B) diagram showing bond angles and distances. (Plain bonds represent bonds in the plane of the image; wedge and dashed bonds represent those directed toward and away from the viewer, respectively.)

In the context of alkenes, cis-2-butene and trans-2-butene are stereoisomers that differ based on the spatial arrangement of their groups relative to the central double bond.12

Cis-2-butene: The two methyl groups are positioned on the same side of the double bond. This configuration is also referred to as (Z)-2-butene, where Z stands for the German word zusammen, meaning "together".12
Trans-2-butene: The two methyl groups are positioned on opposite sides of the double bond. This configuration is also known as (E)-2-butene, from the German word entgegen, meaning "apart".12

While these isomers could theoretically interconvert through rotation around the central bond, this process is not possible under normal conditions because it would require a significant amount of energy—approximately 66 kcal/mol—to overcome the barrier.12