INTRA-MOLECULAR HYDROGEN TUNNELING IN MALONALDEHYDE

Ab initio SCF calculations using an extended basis set were performed in order to determine the tunneling frequency of the interconversion between the two asymmetric forms of β-hydroxyacrolein. Along the reaction coordinate, a double minimum profile with a barrier of 11.6 kcal/mol is found. Due to the value of the effective mass involved in the exchange along the reaction coordinate, the tunneling frequency that results is one order of magnitude less than the experimental value. The double minimum profile obtained when all the atoms but the intervening hydrogen are kept in the average position gives a tunneling frequency which is of the same order as the experimental value. This proton exchange mechanism also explains the change in tunneling frequency when an isotopic species is used. © 1978, American Chemical Society. All rights reserved.