Rotationsbarriere

Rotationsbarriere refers to the energy required to overcome the rotational barrier in a molecule. This barrier arises from the resistance to rotation around a bond, often due to steric hindrance or electronic repulsion between substituents. When considering rotation around a single bond, the energy profile typically shows minima corresponding to more stable conformations, such as staggered arrangements, and maxima corresponding to less stable conformations, such as eclipsed arrangements. The height of these energy maxima represents the rotational barrier.

Understanding rotational barriers is crucial in chemistry for predicting molecular shapes, reactivity, and physical properties. For example, a high rotational barrier around a bond can lead to the existence of stable rotamers, which are distinct stereoisomers that can be isolated. The magnitude of the rotational barrier is influenced by factors such as the size and electronic nature of the atoms or groups attached to the bond, the presence of pi systems, and even solvent effects. Techniques like spectroscopy, particularly Nuclear Magnetic Resonance (NMR), can be used to experimentally determine rotational barriers by observing the interconversion rates between different rotamers at various temperatures. Computational chemistry methods are also widely employed to predict and analyze these energy barriers.