Pushing and pulling electrons: the effect on the heat of formation of trifluoromethyl compounds

The effect on heats of formation, of conjoined or proximate functional groups which can interact via polar or resonance effects, is examined using the –CF 3 group as a standard. Two metrics are applied: the difference in heat of formation of G–CF 3 and G–CH 3 , where –G is a wide range of functional groups, and also the deviation of the heat of formation of G–CF 3 from the average of the heats of formation of G–G and CF 3 –CF 3 . This latter metric reveals both stabilizing and destabilizing effects on the heat of formation, of up to 60 kcal/mol, depending on the polar and resonance nature of the –G structure. The possibility of using such metrics as a correction the group additivity values is examined.