| Abstract
| - The experimental kinetic data for several Diels−Alder reactions show why a 5 M LiClO4−diethylether (LPDE) solution offers maximum enhancement of reaction rates, endo/exo ratios, and yields.These reactions, if carried out in LPDE solutions of concentrations higher than 5 M, show asubstantial decrease in these kinetic parameters. This decrease is attributed to the very highviscosity of LPDE solutions near saturation, though this interpretation is not consistent whenconsidered in terms of sizes of the diene and dienophile. The monoetherates, dietherates, and higherother clusters in LPDE solutions and their relationship with the Lewis acid catalysis by Li+ offera more plausible explanation of both the enhancement and the decrease of the rate of Diels−Alderreactions in this medium.
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