Tetralin bond homolysis

Available rate and thermochemical data allow estimates to be made for bond homolysis rate constants for virtually all covalent bonds presumed or found to be present in coal and model compound reactions. In Table III is compiled a list of coal-related homolysis rate constants, k, and bond homolysis half lives at 400°C, T1/2 (ti/2 = In 2/k is equal to the time required to break one-half of the bonds if homolysis were the only mode of reaction). Most of these values are estimated relative to measured rate constants for bibenzyl dissociation in tetralin, and relative values are expected to be only weakly dependent on solvent. It is evident from Table III, with few exceptions, that only bonds that yield two resonance stabilized radicals upon breaking are likely to undergo significant homolysis under coal liquefaction conditions. 

Formation of Free Radicals by Molecular Disproportionation. A significant conclusion that may be drawn from considerations of rate and equilibrium constants for molecular disproportionation is that this path can provide appreciable concentrations of free radicals in many systems long after most weak chemical bonds have ruptured and bond homolysis has ceased to be a major source of free radicals. In "pure tetralin, for instance, trace concentrations of 1,2-dihydronaphthalene are expected to equilibrate with tetralin and tetralyl radicals,... 

FVP of [5]metacyclophane (4a) (Structures 1) at 600 °C yielded methyl-tetralins 39b and 39c (Structures 10) as the major products via homolysis of the benzylic bond [33c]. On the other hand, FVP of the Dewar isomer 35 produced retralin 39a and methylindans 40a-b via [4]metacyclophane (5) (Scheme 11). Pyrolysis of neat 35 gave dimers 37a-b derived by [4 -t- 2]dimerization of intermediate 5 (Scheme 11) [33a]. 

---