It is interesting that we find the PIC, of V to be 11.5 while that of VI is greater than 13. Thus the order of stability of these systems is reversed when the carbethoxyl group is missing. This may reflect a changed hybridization at carbon when the substituent no longer demands sp2-p hybridization, and we are further investigating systems of this type. However, it is clear from our results that a large extra conjugation effect, such as was predicted from the Koch ...
