Atropisomérie

Atropisomérie is a type of stereoisomerism in which isomers are due to restricted rotation about a single bond. Unlike other forms of stereoisomerism that arise from chiral centers or double bonds, atropisomers are stable compounds that do not interconvert at room temperature because of bulky substituents that hinder free rotation. This restricted rotation creates distinct spatial arrangements, making the molecules non-superimposable mirror images or simply non-superimposable, similar to enantiomers or diastereomers, respectively.

The key requirement for atropisomérie is the presence of bulky groups positioned such that they sterically prevent rotation around a single bond. This often occurs in molecules with biaryl linkages, such as biphenyls, or in certain cyclic structures. The presence of these bulky groups effectively creates an energy barrier to rotation that is high enough to allow for the isolation of individual stereoisomers.

The nomenclature for atropisomers often uses prefixes like R and S, analogous to chiral centers, or designates them based on their relative positions of substituents, such as axial chirality. Understanding atropisomérie is important in fields like organic chemistry, medicinal chemistry, and materials science, as the different spatial arrangements can lead to significant differences in chemical reactivity, biological activity, and physical properties. For example, in drug design, atropisomeric forms might exhibit vastly different pharmacological effects.