Electrostatic effects in the heterolytic

ELECTROSTATIC EFFECTS IN THE HETEROLYTIC DISSOCIATION OF HYDROGEN AT MAGNESIUM OXIDE... 

Electrostatic effects in the heterolytic dissociation of hydrogen at magnesium oxide 247... 

The absence of any effect of deuterium on the rate of reaction and the small extent of deuterium incorporation in the products with CeX suggest that the mechanism is ionic rather than radical. The small amounts of exchange noted could result from the very strong electrostatic fields associated with the Ce " ion causing some heterolytic splitting of the deuterium molecule. In contrast, the enhanced isomerization rates exhibited in the presence of D2O provide added confirmation of the protonic activity of these catalysts, as also does the substantial amount of deuterium incorporation. As Table III indicates, the majority of exchange takes place with the products and is therefore assumed to result from the isomerization process. 

As we discussed in Section 3.4.2, measurements in the gas phase, which eliminate the effect of solvation, show structural trends that parallel measurements in solution but with larger absolute energy differences. Table 3.38 gives A// of gas phase proton dissociation data for some key hydrocarbons. These data show a correspondence with the hybridization and delocalization effects observed in solution. The very large heterolytic dissociation energies reflect both the inherent instability of the carbanions and also the electrostatic attraction between the oppositely charged carbanion and proton that separate. 

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