Pentan2yl

Pentan-2-yl, often written as pentan-2-yl, is an alkyl substituent derived from pentane by removing one hydrogen from the second carbon. It has the chemical formula C5H11 and attaches to a parent molecule through that second carbon, making it a secondary alkyl substituent.

In structure, pentan-2-yl corresponds to a chain where the attachment point is at C-2 of pentane: CH3-CH(-)-CH2-CH2-CH3. The substituent is typically treated as a neutral group in naming, and is one of several common pentyl substituents, alongside pentan-1-yl (n-pentyl) and other isomeric forms such as pentan-3-yl. The pentan-2-yl group is often described as sec-pentyl in older literature, though the IUPAC preferred form is pentan-2-yl.

Stereochemistry can arise with pentan-2-yl-containing compounds. The carbon at the point of attachment bears four different substituents (the hydrogen, the CH3 group, the remaining pentyl chain, and the parent molecule), so in many contexts this center is stereogenic. Consequently, compounds bearing a pentan-2-yl substituent can exist as enantiomers if the surrounding molecular framework is chiral or lacks symmetry; the substituent itself is usually not specified with a fixed configuration unless required.

Applications and usage are in the realm of organic synthesis and naming, where pentan-2-yl serves as a standard secondary alkyl substituent in the construction of more complex molecules.

See also: alkyl substituents, IUPAC nomenclature, stereochemistry.