Carbon compound protonation proton affinity

These species, for oxygen-containing compounds, have a large stability (in excess of 20 kcal mol - ) and require a very loose association. This stability allows for partial proton transfer to the alcohol, even when the ester has a larger proton affinity than the alcohol. The scheme is also consistent with the picture that reactions will take place only at centres prone to form a carbenium ion, namely secondary or tertiary carbon centres. 

The influence of cyclopropyl on the gas phase stability of carbocations as measured by ion cyclotron resonance is shown in Table 14, along with data for some reference compounds. The results are given as gas phase basicities, GB, and proton affinities, PA, defined as AG° and AH°, respectively, for dissociation of the protonated molecule, as in equation 11. In addition hydride affinities D(BH H ) for some cations defined as — AH° for equation 18 are included. For the gas phase basicities and proton affinities the products B are alkenes, amines, nitriles or carbonyl compounds, and thus for these values the stability of the cation is compared to a derivative where the substituent is conjugated with a carbon-carbon or carbon-oxygen double bond, or a nitrogen lone pair, whereas for hydride affinities the products are saturated. 

It is interesting to point out that the lowest proton affinity in polyfluorinated naphthalenes is found for ipso protonation (viz. systems 33, 35 and 36). It is a consequence of the out-of-plane shift of fluorine and the accompanying ring puckering. However, this is at the same time a manifestation of the rr-electron fluoro effect put forward by Liebman et al. [45]. It is very well known that multiply fluorinated compounds possess considerably stabilized a-MOs if the systems are planar, the 7r-manifold being almost unaffected [46]. However, in nonplanar systems all MOs at the carbon skeleton are significantly stabilized [45,46] which is exactly the ceise for the ipso protonation. Now, it can be easily shown... 

Table 4.1 First and second proton affinities (MP2/def2-TZVPP//BP86/SVP in kcalmoh ) and NBO partial charges (BP86/def2-TZVPP//BP86/SVP) at the central carbon q C) for dico-ordinated carbon compounds [18].

The low proton affinities of the solvent molecules allows the development of basic properties for a number of proton acceptors. i, 42 Carbon-halogen compounds, in which the carbon-halogen bond is easily broken with the formation of a stable carbonium ion, act as bases, 43 to give ionized solutions of high conductivities ... 

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