Xylylene comprises two isomeric organic compounds with the formula C6H4(CH2)2. These compounds are related to the corresponding quinones by replacement of the oxygen atoms by CH2 groups. ortho- and para-xylylene are best known, although neither is stable in solid or liquid form. Certain substituted derivatives of xylylenes are however highly stable, an example being tetracyanoquinodimethane.
Synthesis and reactivity
Further heating of the p-cyclophane gives poly(para-xylylene).
At high temperatures, benzocyclobutenes can undergo electrocyclic ring-opening to form o-xylylenes. This and other syntheses of o-xylylenes, and their subsequent dimerization by [4+4] cycloaddition to form cycloctyl structures, were used repeatedly in the synthesis of superphane.
Despite the observed chemistry of para-xylylene (i.e. its rapid polymerization to poly-p-xylylene), which suggests the compound exists as a diradical, physical evidence unanimously concludes that the lowest electronic state of p-xylylene is a closed shell singlet. Additionally, several computational methods confirm this assignment.
- H. E. Winberg, F. S. Fawcett "[2.2]Paracyclophane" Organic Syntheses, Coll. Vol. 5, p.883 (1973); Vol. 42, p.83 (1962) Link.
- R. C. Kerber, E. C. Ribakove "Formation of iron carbonyl complexes of reactive polyenes from dihalides involving the free polyene" Organometallics, 1991, volume 10, pp 2848–2853.doi:10.1021/om00054a059
- Sekine, Y.; Brown, M.; Boekelheide, V. (1979). "[220.127.116.11.2.2](1,2,3,4,5,6)Cyclophane: superphane". Journal of the American Chemical Society. 101 (11): 3126–3127. doi:10.1021/ja00505a053.
- Montgomery, L. K., Huffman, J. C., Jurczak, E. A. & Grendze, M. P. The molecular structures of Thiele’s and Chichibabin’s hydrocarbons. J. Am. Chem. Soc. 108, 6004–6011 (1986) DOI:10.1021/ja00279a056