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Pyrrolidine is a saturated five-membered heterocycle containing one nitrogen atom, with formula ${\mathrm{C}}_4{\mathrm{H}}_9\mathrm{N}$. As a secondary amine, it can accept a proton and participate as a nitrogen nucleophile.

Unlike pyrrole, its ring has no aromatic pi system tying up the nitrogen lone pair. Distinguishing the saturated and aromatic heterocycles is therefore important when predicting basicity and reactivity.

The anion formed by N–H deprotonation of pyrrole. It can bind through nitrogen as a two-electron ${\eta }^1$ donor, or through its aromatic ring as a six-electron ${\eta }^5$ donor. Specifying hapticity is essential for electron counting.