Methane stability/destabilization

Substitution of either electron donating or withdrawing groups in para or meta position in phenyl azotriphenyl methanes lead to small changes in decomposition rates . Two interpretations have been put forward. According to one, the phenyl radical is stabilized by electron accesssion and destabilized by electron depletion and according to the other, desolvation in the transition state plays a role in the rate controlling step . 

All perfluoroalkyl carbanions are stabilized by the negative inductive effect —If) of their fluoro substituents. At the same time, a-fluoro carbanions are destabilized by electronic p-tr repulsion of the lone electron pairs of the fluorine and at the anionic center (+f effect). This is reflected in the relatively weak acidity of CHF, in comparison with the other haloforms - the pfQ values of the various trihalo-methanes are CHF, 30.5, Cl ICI, 22.4, CHBr, 22.7, and Cl I, 68-70 [34]. 

Heats of formation are calculated as a sum of the bond energies and other stabilizing and destabilizing (e.g., strain) increments for the structure. MM4 calculations include terms for contributions of higher-energy conformations. For a set of hydrocarbons ranging from methane and ethane to adamantane and bicyclo[2.2.2]octane, the heats of formation are calculated with a standard deviation of 0.353 kcal/mol. The MM4 system has also been applied to alkenes, ° aldehydes, and ketones. ... 

RSE of 51 compared to 2-propyl radical was measured as 16 kcaFmol, and flie BDE of diphenyl-methane (81.8 kcal/mol) was essentially the same as that of fluorene. It has been noted radicals centered on 5-membered rings gain little additional stability by conjugation with extended aromatic networks . Considering the doubts raised about antiaromaticity in the fluorenyl cation, it is perhaps surprising there is evidence of significant destabilization in the radical 51. 

Figure9.l I shows a Walsh diagram for opening two H—C—H angles in methane from the tetrahedral geometry 6 = 109.47°) to the square plane 6 = 180.0°). During the Td D4h distortion, two members of the It2 set are stabilized, e <0, since overlap between the p orbital on A and the two hydrogen s orbitals is increased and these are bonding MOs. But the third member is destabilized, > 0, since all bonding...

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