Torsjonsbarriere

Torsjonsbarriere, also known as rotational barrier, refers to the energy required to rotate a chemical bond between two atoms. This energy is typically overcome by thermal motion at room temperature, allowing for rotation. However, in certain cases, the energy barrier can be significant, restricting or preventing rotation. This phenomenon is particularly important in the study of molecular conformations and their stability.

The height of the torsjonsbarriere is influenced by several factors, including steric hindrance between substituents on the bonded atoms, electronic interactions such as pi-electron delocalization, and dipole-dipole repulsions. For single bonds like C-C bonds, the torsjonsbarriere is generally low, allowing for free rotation. For double bonds, like C=C bonds, the torsjonsbarriere is very high, making rotation impossible without breaking the bond. This is why alkenes exhibit cis-trans isomerism.

In more complex molecules, specific functional groups or structural features can create significant torsjonsbarriere. For instance, the restricted rotation around amide bonds in peptides is crucial for protein folding. Spectroscopic techniques like Nuclear Magnetic Resonance (NMR) can be used to study and quantify torsjonsbarriere by observing the interconversion rates of different conformations. Understanding torsjonsbarriere is fundamental in organic chemistry, physical chemistry, and biochemistry for predicting molecular shapes, reactivity, and physical properties.