Cyclopentyne

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]

Cyclopentyne

Names
Preferred IUPAC name Cyclopentyne
Identifiers
CAS Number	1120-58-7
3D model (JSmol)	Interactive image
PubChem CID	14093813
UNII	YW3RQN2WZY
CompTox Dashboard (EPA)	DTXSID10555814
InChI InChI=1S/C5H6/c1-2-4-5-3-1/h1-3H2 Key: CPGPQFYAGKHQTB-UHFFFAOYSA-N
SMILES C1CC#CC1
Properties
Chemical formula	C5H6
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). Infobox references