AM1 CALCULATIONS OF SUBSTITUENT EFFECTS IN RETRO-DIELS-ALDER REACTIONS

The AM1 method has been used for investigating the effects of substituents on retro-Diels-Alder reactions, and the results have been compared with experimental data. Transition structures for butadiene reacting with ethylene and acrolein are quite close to those obtained with ab initio methods. The calculated asynchonicity of the retro-Diels-Alder reaction of substituted bicyclo[2.2.2]octa-2,5-dienes and ethanoanthracenes depends on substituents, with electron-donating groups making the TS more asymmetrically. The calculated activation energies for these reactions are too high compared to experimental data, but trends in relative activation energies for different substituents are reproduced reasonably well, although there are exceptions. Calculated activation entropies for unsubstituted systems are in good agreement with ab initio values and experimental data, but the variation of activation entropy with substituents is not reproduced. © 1990, American Chemical Society. All rights reserved.