Transisoisomerism

Transisoisomerism is a type of stereoisomerism where two atoms or groups of atoms attached to a double bond have the same substituents on opposite sides of the double bond. This geometric arrangement arises due to the restricted rotation around the double bond. The term "trans" refers to the positions of these identical substituents, indicating they are on opposite sides.

For example, in the case of but-2-ene, one isomer has the two methyl groups on the same side of the double bond (cis-but-2-ene), while the other isomer has them on opposite sides (trans-but-2-ene). Transisoisomers are generally more stable than their cis counterparts due to reduced steric hindrance between the larger groups. This difference in stability can lead to different physical properties, such as melting points and boiling points, and can also affect chemical reactivity.

Transisoisomerism is a crucial concept in organic chemistry and is observed in various molecules, including alkenes, cyclic compounds, and oximes. Understanding transisoisomerism is essential for predicting molecular properties and designing chemical reactions. The nomenclature for indicating transisomers often involves prefixes like "trans-" or the E/Z system, which provides a more systematic way to describe the configuration of substituents around a double bond.