prop2en1yl

Prop-2-en-1-yl, commonly known as the allyl group, is a three-carbon substituent derived from propene. In IUPAC terminology the substituent is named prop-2-en-1-yl, indicating attachment to the parent molecule at carbon 1 of a three-carbon chain and a carbon–carbon double bond between carbons 2 and 3. The neutral, uncharged substituent has the formula C3H5 and is best represented by the structure CH2-CH=CH2, where the CH2 at the left is the point of attachment to the parent compound.

The allyl group is a primary allylic substituent; its pi system is conjugated across the three-carbon fragment, stabilizing allylic cations and radicals. Because of its conjugation, it participates readily in allylic substitution and radical reactions. It is also widely used in organic synthesis as a protecting group for alcohols (allyl ethers) and as a leaving or reactive handle in allylation reactions such as the Tsuji–Trost reaction.

Common synonyms include allyl, 2-propenyl, and prop-2-en-1-yl. The term prop2en1yl is a condensed form used in some databases or notation for the same substituent. The E/Z designation does not apply to the substituent itself, as the double bond is terminal.

In summary, prop-2-en-1-yl (allyl) is a versatile allylic substituent essential in synthesis and polymer chemistry, offering both reactivity at the allylic position and compatibility with protective strategies.