Molecular orbital study on the mechanism of radical polymerization of spiro-orthocarbonates bearing exo-methylene groups
✍ Scribed by Fumio Sanda; Toshikazu Takata; Takeshi Endo
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 433 KB
- Volume
- 4
- Category
- Article
- ISSN
- 1022-1344
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✦ Synopsis
Molecular orbital studies were carried out to compare the easiness of ring-opening in the radical polymerization of spiro-orthocarbonates bearing exo-methylene groups at a-position of the ether oxygen, spiro[2,4-benzodioxepine-4'-methylene-3,2'-[1,3]-dioxolane] (l), and at /%position of the ether oxygen, spiro[2,4-benzodioxepine-5'-methylene-3,2'-[1,3]-dioxane] (2). The formation energy suggests that 1 would show a degree of ring-opening larger than 2, contrary to the experimental result. Therefore, a reverse relation in activation energy was suggested, i. e., the kinetic factor surpasses the thermodynamic factor in the ring-opening reaction of 1 and 2. Although the calulation of the activation energy of the radical ring-opening reaction was not successful, the result extracted from the perturbation energy calculations of vinyl polymerizations of 1 and 2 agree well with their radical vinyl polymerizability. Namely, 1 was confirmed to have a larger vinyl polymerizability than 2, which agrees well with the smaller ring-opening polymerizability of 1 compared with 2. The real HOMO and LUMO (highest occupied and lowest unoccupied molecular orbitals) of 1,2 and their intermediates for the radical addition were confirmed not to correspond to the apparent HOMO and LUMO from the detailed analysis of their coefficients of atomic orbitals (AOs). The frontier electron density of 1 and 2 agrees well with the fact that the B-carbon of their exo-methylene group has a higher reactivity toward radical species than the a-carbon.