Fluorinated reactive intermediates energies

Systematics and Surprises in Bond Energies of Fluorinated Reactive Intermediates... 

These vdW states stand in contrast to the more conventional transition state resonances, such as for F + HDHF + which are localized near the reaction barrier and thus possess partially formed/broken bonds. The usual interpretation of the latter conventional reactive resonances is to associate them with states trapped in vibrationally adiabatic potential wells that occur in the vicinity of the transition state. Instead, the pre-reactive and post-reactive vdW resonances are only weakly perturbed from the reagent or product states. The Born-Oppenheimer potential energy surface (PES) for the vdW case is dominantly repulsive, exhibiting only shallow entrance or exit channel wells. This is also unlike other reactions such as 0( P) + OH- 02 + H for which the intermediate is an activated molecule (HO2) where the PES has a deep trapping well and the resonance states are very dense and overlapping. As an illustration of the influence of this sort of vdW reactive intermediate on the reaction observables, we consider the case of the reaction of HCl with ground state fluorine atoms. 

In order to obtain some insight concerning the effect of fluorine on metabolic activation of fluorinated PAHs, isodesmic reactions (Figure 12) were calculated as a measure of the relative ease of formation of the fluorinated epoxides. Almost no energy differences were observed, consequently formation of these intermediates could be assumed not to be as relevant as carbocation formation in determining the relative reactivity of the ultimate metabolites. 

In a molecule, fluorine atoms influence bond energies, electronic distribution, acidity, hydrogen bonds, steric interactions, and the stability of intermediate entities in a transformation. These factors, which have great influence on chemical reactivity, are examined. 

As the data accumulate, the low rates of addition compared to many of the atoms will be evident, and the relatively low sensitivity to structural variation in the olefin should be noted. The relative reactivities of the radicals increase with increasing fluorine substitution, by a factor of nearly 1000 between CH3 and CF3 radicals. Few data are available for the intermediate fluorinated radicals, CHjF and CHFj. The only available evidence is reported in Table 56, along with comparable values for the CH3, CF3 and CCI3 radicals. The A factors vary little, but the activation energies are extremely sensitive to fluorine content, and the latter is the principal reason for the substantial variations in the rate. The CCI3 radical, on the other hand, has almost exactly the same reactivity as the methyl radical. 

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