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In organic chemistry, a xylylene (sometimes quinone-dimethide) is any of the constitutional isomers having the formula C6H4(CH2)2. These compounds are related to the corresponding and 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. The meta form is a diradical. Certain substituted derivatives of xylylenes are however highly stable, such as tetracyanoquinodimethane and the xylylene dichlorides.
Further heating of the p-cyclophane gives Parylene.
α,α'- ortho Xylene dibromides have been well developed for generating o-xylyenes. For example, reaction of tetrabromo-o-xylene (C6H4(CHBr2)2) with sodium iodide affords α,α'-dibromo-o-xylylene, which can be trapped to give naphthylene derivatives. In the absence of trapping agents, the xylylene relaxes to α,α'-dibromobenzocyclobutane:
The diene unit formed by the two exocyclic alkene units of the ortho isomer can serve as a ligand in coordination complexes. For example, reaction of α,α'-dibromo- o-xylene with affords low yields of the xylylene complex Fe(CO)3η4-C6H4(CH2)2. This product is structurally analogous to Fe(CO)3η4-1,3-butadiene.
At high temperatures, 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.
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