Ground-state modeling

Reich and Cram 8 > studied the patterns of electrophilic substitution of the monosubstituted [2.2]paracyclophanes. It was at once clear that the directive influences of the substituents X (see below) could not be correlated with transannular resonance effects in the ground state 84>. The product pattern predicted on the basis of electrostatic ground-state models, such as the canonical structures 65 for electron-releasing and 66... 

The ground state geometries of the TT steps in the three hairpins Stl, St3 and St5 play important roles in the formation of the TT steps as evidenced by the order of magnitude agreement between predictions from our model and experimental values. The subtle differences between the TT dimer quantum yields of Stl, St3 and St5 seen in experiment are not reproduced with our model. This implies our model is not capturing some of the subtle and yet important behavior of these systems. This could be due to anything from a lack of a refined ground state model to the need to incorporate an electronic effect. 

So far we have seen two sets of systems in which our ground state model for predicting photoinduced TT dimer yields works well (Sects. 13.3 and 13.5). The model failed to predict the subtle trend in TT dimer yields of hairpins Stl, St3 and St5 in Sect. 13.4 and yet was able to predict quantum yields for each species that were within an order of magnitude of experimental results. In this section we further test the limits of our ground state model by investigating sequence specificity in TT dimer yields more closely. 

Let us define the projector on to the ground-state model eigenfunction as... 

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