kiertämisakselit

Kiertämisakselit, also known as chiral axes or axial chirality, describe a type of stereoisomerism where a molecule possesses chirality due to the arrangement of substituents around an axis rather than a traditional chiral center. This means that the molecule cannot be superimposed on its mirror image, even though it may lack a carbon atom bonded to four different groups.

The concept of axial chirality is particularly relevant in organic chemistry and is observed in various molecular structures. Common examples include allenes, where the cumulative double bonds create a situation where the groups on the terminal carbon atoms are arranged perpendicularly, leading to axial chirality. Biphenyls substituted in such a way that rotation around the single bond connecting the two phenyl rings is restricted can also exhibit axial chirality. This restriction often arises from bulky substituents at the ortho positions of both rings, preventing free rotation. Other examples include certain substituted paracyclophanes and helical molecules.

Determining the chirality of a molecule with an axial chirality requires considering the spatial arrangement of the substituents around the axis. The designation of stereochemistry, often using notations like R and S, is based on specific rules that take into account the priority of groups and the direction of their arrangement around the chiral axis. Molecules with axial chirality are optically active, meaning they rotate the plane of polarized light. This property is crucial in various fields, including pharmacology and materials science, where the specific three-dimensional structure of a molecule can profoundly influence its biological activity or physical properties. Understanding axial chirality is essential for a complete understanding of molecular stereochemistry and isomerism.