describe cis-trans isomerism

Cis-trans isomerism, also known as geometric isomerism, is a type of stereoisomerism describing the orientation of functional groups within a molecule. Here's a step-by-step description:

1. Definition: Cis-trans isomers are a type of stereoisomers, which means they have the same molecular formula and sequence of bonded atoms, but a different spatial orientation.

2. Cis Isomer: In a cis isomer, the functional groups are on the same side of the molecule. This can cause the molecule to be polar, and can affect its physical and chemical properties.

3. Trans Isomer: In a trans isomer, the functional groups are on opposite sides of the molecule. This often results in a more symmetrical and nonpolar molecule.

4. Double Bonds: Cis-trans isomerism occurs in molecules with restricted rotation, most commonly around carbon-carbon double bonds. This is because the pi bond in a double bond prevents the atoms from rotating freely around the bond axis.

5. Importance: The different spatial arrangements of cis-trans isomers can result in different physical and chemical properties, such as boiling point, density, and reactivity. This makes cis-trans isomerism important in fields like biochemistry and pharmaceuticals.

6. Example: An example of cis-trans isomerism is but-2-ene. The cis isomer has the two methyl groups on the same side of the double bond, while the trans isomer has them on opposite sides. Despite being made of the same atoms, these two isomers have different properties.