“Xylylene”的意思、由来-开放百科全书

词条

Xylylene

释义

Synthesis and reactivity
Electronic structure
References

{{double image|right|o-xylylene.png|93|p-xylylene.png|152|ortho-Xylylene|para-Xylylene}}

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

p-Xylylene forms upon pyrolysis of p-xylene or, more readily, the α-substituted derivatives (see equation). Upon condensation, p-xylylene dimerizes with moderate efficiency to give p-cyclophane:^[1]

Further heating of the p-cyclophane gives poly(para-xylylene).

The reaction of α,α'-dibromo-o-xylene with iron carbonyls affords low yields of the xylylene complex Fe(CO)₃[η⁴-C₆H₄(CH₂)₂]. This complex is similar to Fe(CO)₃[η⁴-1,3-butadiene].^[2]

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.^[3]

Electronic structure

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.^[4]

References

1. ^H. E. Winberg, F. S. Fawcett "[2.2]Paracyclophane" Organic Syntheses, Coll. Vol. 5, p.883 (1973); Vol. 42, p.83 (1962) Link.
2. ^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}}
3. ^{{cite journal|last1=Sekine|first1=Y.|last2=Brown|first2=M.|last3=Boekelheide|first3=V.|title=[2.2.2.2.2.2](1,2,3,4,5,6)Cyclophane: superphane|journal=Journal of the American Chemical Society|volume=101|issue=11|pages=3126–3127|year=1979|doi=10.1021/ja00505a053}}
4. ^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

1 : Cyclohexadienes

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