1-(2-Pyrimidinyl)piperazine (1-PP, 1-PmP) is a chemical compound and piperazine derivative. It is known to act as an antagonist of the α2-adrenergic receptor (Ki = 7.3–40 nM) and, to a much lesser extent, as a partial agonist of the 5-HT1A receptor (Ki = 414 nM; Emax = 54%). It has negligible affinity for the dopamine D2, D3, and D4 receptors (Ki > 10,000 nM) and does not appear to have significant affinity for the α1-adrenergic receptors. Its crystal structure has been determined.