3-Ethynyl-2,2,5,5-tetra-methyl-1-oxyl-3-pyrroline.

The five-membered ring of the title compound, C10H14NO, is almost planar [mean deviation from best plane = 0.006 (1) A]. The N—O bond is in the plane of the five-membered ring. The mol­ecule is positioned about a pseudo-mirror plane at y = 0.375. In the crystal, mol­ecules are connected by inter­molecular C—H⋯O contacts into layers parallel to (010).