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AB Initio Study Of Bond Breaking In Olefins. GVB Computations On Propene  Methyl + Vinyl And Propene  H+Propen-2-Yl

Y.Moussaoui, O.Ouamerali, George R.De Mare

The Generalized-Valence-Bond-Perfect-Pairing (GVB-PP) method is used to investigate the structural behaviour, energy, and dipole moment along the reaction coordinates for (1) propenemethyl+vinyl and for(2) propeneH+propen-2-yl. Geometry optimisations are carried out at the GVB(9)/STO-3G level (complete valence shell) for the minimum energy propene structure and for numerous structures up to r(C2-C3) and r(H3-C2)=10A(only the elongated C2-C3 and C3-H2 distances are kept fixed, respectively). Both dissociation curves are smooth, without a maximum, and yield predicted dissociation energies for reaction(1) and (2) of 499.1 and 543.6 kJ.mol-1, respectively. (The latter value is about 10 kJ.mol-1 lower than those predicted for the primary (C-H) bond ruptures in propene, using the same method and basis set) GVB(7)/ 6-31G//GVB(9)/STO-3G computations lower the predicted dissociation energies for reactions(1) and (2) to 392.6 kJ.mol-1 and 435.7 kJ.mol-1, respectively. CCSD/cc-pVDZ calculations yield intermediate dissociation energies of 427.6 and 460.5 kJ.mol-1 for reactions(1) and (2), respectively. Linear behaviour is observed at long bond distances when the reduced energy concept, ER=(Er - E8)/De, is applied to the reaction coordinates.