MODEL-CALCULATIONS OF BASE-CATALYZED 1,3-PROTON TRANSFER-REACTIONS IN INDENE-LIKE SYSTEMS

The geometries and heats of formation for stationary points on the potential energy surface (PES) for the prototropic rearrangement reactions of 1-methylcyclopentadiene and 1-methylindene, respectively, catalysed by ammonia, have been calculated by the PM3 method. The model used includes eight water molecules to simulate specific interactions of a polar solvent with the reactant molecules. After the initial transfer of the proton from the carbon acid to ammonia, the PES is found to be very flat, with almost free mobility of the ammonium ion above the 1-, 2- and 3-positions of the anions.