Solvent Effects on Isopolar Transition State Reactions

3 Solvent Effects on Isopolar Transition State Reactions 

Some concerted [m + n] cycloaddition reactions , however, have been well examined [90-93], e.g. Diels-Alder reactions [114-116] and 1,3-dipolar cycloaddition reactions [117-120, 541-543]. Both of these reactions have been established as concerted [4 + 2] cycloaddition reactions. 

The solvent effect on the bimolecular rate constant of a Diels-Alder reaction is usually quite small. As a rule, in going from nonpolar to polar solvents, the rate constant increases only by a factor of about 3... 20 [34, 35, 121-130, 531-537]. 

Typical examples are the cycloaddition of isoprene and maleic anhydride as shown in Eq. (5-42) [127], and the dimerization of cyclopentadiene icf. Table 5-1 in Section 5.2) [33, 34]. 

Solvent ( -C3Hv)20 CeHe CeHsCl CH3NO2 CfiHjNOz o-Dichlorobenzene 

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