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Preferred IUPAC name
3D model (JSmol)
  • InChI=1S/C5H6/c1-2-4-5-3-1/h1-3H2
  • C1CC#CC1
Molar mass 66.103 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Cyclopentyne is a cycloalkyne containing five carbon atoms in the ring. Due to the ideal bond angle of 180° at each atom of the alkyne but the structural requirement that the bonds form a ring, this chemical is a highly strained structure, and the triple bond is highly reactive. The triple bond easily undergoes both [2+2] and [4+2] cycloaddition reactions.[1] Unlike benzyne, which undergoes a [2+2] addition with loss of stereochemistry at the alkene partner, cyclopentyne reacts with alkenes with retention of geometry of the partner,[2] an example of the relevance of orbital symmetry even for highly reactive structures.[3] The structure can also form a π complex with lithium cations, which affects the cycloaddition reactivity.[1] It can even interact strongly enough with copper species to form a novel type of metallacycle.[4]


  1. ^ a b Gilbert, John C.; Hou, Duen-Ren (2003). "Competitive Intermolecular Pericyclic Reactions of Free and Complexed Cyclopentyne". J. Org. Chem. 68: 10067–10072. doi:10.1021/jo0352880.
  2. ^ Ozkan, Ilker; Kinal, Armagan (2004). "Competing Pathways in the [2+2] Cycloadditions of Cyclopentyne and Benzyne. A DFT and ab Initio Study". J. Org. Chem. 69 (16): 5390–5394. doi:10.1021/jo049542f.
  3. ^ Gilbert, John C.; Hou, Duen-Ren (2004). "Stereochemistry of the [2+4] cycloaddition of cyclopentyne". Tetrahedron. 60 (2): 469–474. doi:10.1016/j.tet.2003.11.003.
  4. ^ Arslancan, Serra; Lamsabhi, Al Mokhtar; Mó, Otilia; Yáñez, Manuel (2017). "Complexes between cyclopentene and cyclopentyne derivatives with HCu and FCu. The importance of cyclization effects". International Journal of Quantum Chemistry. doi:10.1002/qua.25489.