The site of radical attack at the furan ring from MNDO calculations

The semi-empirical SCF MNDO method has been used to calculate the radical reactivities for each reaction site in some neutral furan molecules as the average of the HOMO and LUMO probabilities both in 2p_z atomic orbitals 1

1 SCF: Self-consistent field; MNDO: modified neglect of differential overlap; HOMO: highest occupied molecular orbital; LUMO: lowest unoccupied molecular orbital.

. The carbon atoms C⁵ and C² of of the furan ring are the most favoured sites except for the furan derivatives holding a double bond in the substituent group. Also the SOMO 2

2 SOMO: Single occupied molecular orbital.

probabilities of the radicals formed by addition of a hydrogen atom or a vinyl acetate model radical were calculated. Thus, once a radical is added to the C⁵ position the resulting radical can be partially localized on the carbon C². Furthermore, the enthalpy of reaction for several radicals was estimated by using the calculated heats of formation of the neutral furan molecules and their radicals. The radical addition to the carbon C ⁵ resulted in the most exothermic reaction in comparison with other reaction sites of the molecule. However, no correlation was found between the calculated enthalpies and the degradative-transfer kinetic constants experimentally determined for the radical polymerization of vinyl acetate in the presence of the furan compounds under study.