A simple method of estimating homolytic bond dissociation energies (BDEs) in Me^O solution for H-A type substrates has been devised by combination of their equilibrium acidities, p£HA, and the oxidation potentials of their conjugate bases, £0X(A~), by using an equation derived from a thermodynamic cycle. For 9-methylanthracene, diphenylmethane, triphenylmethane, cyclopentadiene, indene, fluorene, acetone, thiophenol, phenol, and aniline reasonable agreement with gas-phase BDEs was obtained. The method has been extended to the benzylic C-H bonds in phenylacetonitrile, ethyl phenylacetate, and benzyl phenyl sulfone for which gas-phase BDEs do not appear to be available. The effects of CN, C02Et, and S02Ph groups on the C-H BDEs, relative to that in toluene in these three compounds, were found to correspond closely to the effects of CN, CQ2Me, and S02Ph groups on the 9-C-H BDEs in 9-substituted fluorenes, relative to that in fluorene.

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angular 4mr conjugated polycycles, exemplified by phenanthrene dianion 32~, sustain larger antiaromatic contributions than are exhibited by the linear systems. This theoretical-based assumption is now clearly demonstrated experimentally by the anions derived from dibenzotetracene (1) and 9-(9'-phenanthryl)anthracene (4). Experimental SectionDibenzotetracene (1) was prepared by a bis-Wittig reaction between phenanthrenequinone and the bis(triphenylphosphine) dibromide salt derived from 2,3-dimethylnaphthalene. The reaction was conducted under phase-transfer catalysis conditions using LiOH as a base.16 9-(9'-Phenanthryl)anthracene (4) was prepared by a Grignard reaction between 9-phenanthrylmagnesium bromide and anthrone in a mixture of dry benzene and THF. The reaction was conducted at room temperature for 24 h while strict anhydrous conditions and nitrogen atmo-6762 J.

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