unimolekylær

Unimolekylär refers to a process or reaction that involves a single molecule. In chemistry, a unimolecular reaction is a reaction in which, on the molecular scale, only a single molecule is involved in the rate-determining step. This means that the reaction rate depends only on the concentration of that single reactant molecule. For example, the decomposition of a molecule into two or more fragments is a common type of unimolecular reaction. Another example is the rearrangement of atoms within a single molecule to form an isomer.

The concept of unimolecularity is fundamental in chemical kinetics, the study of reaction rates. While reactions may involve multiple steps, the slowest step, known as the rate-determining step, dictates the overall speed of the reaction. If this slowest step involves only one molecule, the reaction is classified as unimolecular. This contrasts with bimolecular reactions, where two molecules collide and interact in the rate-determining step, and termolecular reactions, where three molecules are involved.

In biological contexts, unimolecular processes can also occur. For instance, the conformational change of a protein or the isomerization of a substrate within an enzyme active site can be considered unimolecular events if only one molecule is directly participating in the transformation. The term unimolecular emphasizes the singular involvement of a single molecular entity in a specific chemical or physical transformation.