Ab initio study of the reactivity and plausible polymerization process of a labdatriene monomer

The feasibility of the different initial reaction pathways in the gas-phase polymerization of labdatriene monomers, important constituents in amber re sins, has been analyzed through ab initio electronic structure calculations . Based on the computed values of density functional theory local Fukui fun ctions and softnesses, tendencies towards free radical additions were quant itatively derived. Results indicate those unsaturated carbons at the diene group 12 and 15 positions possess higher reactivity towards addition reacti ons. This implies that, in the gas phase, 1,4-addition is the most favored in the ground state. A simple model to account for intermolecular forces an d their possible effects to modify the predicted reactivity does not sugges t that these forces may be significant to indeed modify it. However, our fr ontier orbitals calculations suggest the initial formation of a triplet exc ited state in order to prepare the rr-conjugated labdane monomer to undergo the experimentally observed 3,4-addition. (C) 2000 Elsevier Science Ltd. A ll rights reserved.