Solvent effect on the volume of activation and volume of the Diels-Alder reaction

Volumes of activation, DeltaV(not equal), and reaction, DeltaV, partial mol ar volumes, (V) over bar, and enthalpies of solution, Delta H-sol, were det ermined for tetracyanoethylene, cyclopentadiene, 1,3-butadiene, trans, tran s-1,4-diphenyl-1,3-butadiene and their Diels-Alder adducts at 25 degreesC i n some solvents of pi- and n-donor type. The values of the activation and r eaction volumes were exceptionally small in the former type of solvents. La rge solvent effects on Delta H-sol(TCNE) (up to 26 kJ mol(-1)), (V) over ba r (TCNE), DeltaV and DeltaV(not equal) (up to 11 cm(3)mol(-1)) were observe d in aromatic solvents and these values are linearly correlated with each o ther. Poor correlations were found for n-donor solvents, but a linear depen dence between AV and delta Hr-n (enthalpy of reaction) was obtained for all solvents. Copyright (C) 2001 John Wiley & Sons, Ltd.