Xylylene


Xylylene comprises two isomeric organic compounds with the formula C6H42. 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

p-Xylylene forms upon pyrolysis of p-xylene or, more readily, the α-substituted derivatives. Upon condensation, p-xylylene dimerizes with moderate efficiency to give p-cyclophane:
Further heating of the p-cyclophane gives poly.
The reaction of α,α'-dibromo-o-xylene with iron carbonyls affords low yields of the xylylene complex Fe3. This complex is similar to Fe3.
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 cycloaddition to form cycloctyl structures, were used repeatedly in the synthesis of superphane.

Electronic structure

Despite the observed chemistry of para-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.