The possible effects of electron correlation on Hckel-type rules for cyclic -electron systems are considered. General exact results are developed for a wide variety of models, including a range of degrees of electron correlation, for homo- or heteroannulenes or various distorted cycles, either of Hckel or Mbius type. The theorematic results confirm some general qualitative points of the Hckel-type rules and provide checks on approximate solutions to these various models. 1984 American Chemical Society.
