Pericyklischer

Pericyklischer is a German term that translates to “pericyclic” in English. It pertains to a class of organic chemical reactions characterized by a concerted cyclic redistribution of bonding electrons among participating molecules or intermediates. These reactions typically involve the simultaneous making and breaking of bonds within a cyclic transition state, leading to the formation of new chemical structures.

Pericyclic reactions encompass several well-known types, including cycloadditions, electrocyclizations, sigmatropic rearrangements, and double bond shifts. They are notable for their stereospecificity and often proceed via thermally allowed pathways that are governed by orbital symmetry rules, such as the Woodward-Hoffmann rules. These rules predict whether a particular pericyclic reaction will occur under thermal or photochemical conditions based on the symmetry properties of the frontier molecular orbitals involved.

The concept of pericyclic reactions was significantly developed in the 1960s through the work of Robert B. Woodward and Roald Hoffmann, who received the Nobel Prize in Chemistry in 1981 for their contributions. Understanding pericyclic reactions is crucial in organic synthesis, as their predictable stereochemical outcomes facilitate the construction of complex natural products and pharmaceuticals.

In summary, pericyklischer reactions are a fundamental class of organic transformations distinguished by their cyclic electron redistribution mechanisms and strict stereochemical control. They continue to be a central concept in mechanistic organic chemistry and synthetic strategy development.