Allyyliryhmän

Allyyliryhmään, commonly referred to as the allyl group in English, is an organic functional group composed of a three-carbon chain with a terminal double bond (CH2=CH–CH2–). It is represented by the shorthand -CH2CH=CH2. The group is planar at the double bond, and the carbon atoms adjacent to the double bond are sp2 hybridized, while the terminal CH2 is sp3. Because of the conjugated π system, the allyl group can delocalize electron density, which influences its chemical behavior.

The allyl group is a common building block in organic synthesis, particularly in reactions that involve radical, cationic, or nucleophilic substitution. Its ability to stabilize adjacent positive charges via resonance makes it popular in allylic alkylation, Claisen condensation, and various transition‑metal catalyzed processes. Allyl derivatives such as allyl alcohol, allyl chloride, and allyl bromide are frequently employed as starting materials.

In organic chemistry, the presence of an allyl group alters the acidity of adjacent hydrogens and can participate in cycloaddition reactions like the Diels‑Alder reaction, where it can serve as a 1,3-diene fragment. The group’s stereochemistry is typically unimportant because the alkene is planar, but in certain reactions it can be controlled to produce chiral centers.

Because of its resonance stabilization, allyl compounds are relatively resistant to oxidation compared to other unsaturated systems, yet they are reactive enough to participate in nucleophilic additions. This balance of stability and reactivity makes the allyl group an indispensable motif in medicinal chemistry, material science, and the synthesis of natural products.

Overall, allyyliryhmään or the allyl group plays a vital role as a versatile and reactive scaffold in modern organic chemistry.