The Effect of Pressure on Retro Diels–Alder Reactions

✍ Scribed by Frank-Gerrit Klärner; Volker Breitkopf

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 333 KB
• Volume: 1999
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/(sici)1099-0690(199911)1999:11<2757::aid-ejoc2757>3.0.co;2-j

✦ Synopsis

The activation and reaction volumes (∆V /∆V) were showing negative volumes of activation (∆V Ͻ 0) whereas the others are slightly retarded (∆V Ͼ 0). From the analysis determined for the retro Diels-Alder reactions of the parent dihydrobarrelene 1a, its 2-cyano derivative 1b, the exo and of the volume data including the van der Waals volumes (V w ) one can conclude that the packing coefficients of the endo Diels-Alder adducts of maleic anhydride to naphthalene exo-, endo-4, and the exo and endo Diels-Alder pericyclic transition states are equal to or even larger than those of the corresponding Diels-Alder adducts. This finding adducts of N-phenylmaleic imide to 6,6-dimethylfulvene exo-, endo-8 from the pressure dependence of the rate may be explained with the restriction of the degrees of freedom in the transition states leading to a contraction of constants and the partial molar volumes (V) of reactants and products at various temperatures. The cleavage of exo-4, the expansion volume. endo-4, and exo-8 are slightly accelerated by pressure [a]