Cyclopentanone
= Cyclopentanone
<Cyclopentanone> is a five-membered cyclic <ketone> with formula $\mathrm{C_5H_8O}$. Its carbonyl carbon is part of the ring, rather than attached to a separate cyclic substituent.
The neighboring carbons can form enolates, so the molecule is a useful substrate for carbonyl addition, reduction, and alpha-carbon functionalization. Ring geometry constrains the conformations available to those reacting groups.