Cyclopentyne

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

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]

References

^ ^a ^b Gilbert, John C.; Hou, Duen-Ren (2003). "Competitive Intermolecular Pericyclic Reactions of Free and Complexed Cyclopentyne". J. Org. Chem. 68 (26): 10067–10072. doi:10.1021/jo0352880. PMID 14682701.
^ 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. PMID 15287786.
^ 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.
^ 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. 118 (9). doi:10.1002/qua.25489.

[GilbertJOC2003-1] Gilbert, John C.; Hou, Duen-Ren (2003). "Competitive Intermolecular Pericyclic Reactions of Free and Complexed Cyclopentyne". J. Org. Chem. 68 (26): 10067–10072. doi:10.1021/jo0352880. PMID 14682701.

[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. PMID 15287786.

[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. 118 (9). doi:10.1002/qua.25489.

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