Fluorinated cyclacenes - AM1 treatment

The peripherally fluorinated Huckel type cyclacenes having 3-7 benzenoid rings (R) were considered for AM1 (restricted Hartree-Fock) type semiempirical quantum chemical treatment. The cyclacenes having one or two of the peripheries completely fluorinated constitute type-I and type-H structures, respectively. All of them were found to be stable. Type-I systems are endogenic but type-II structures, R:5 onwards are exogenic. The cryptoannulenic effect was found to be operative partly on the heats of formations of type-I systems. Whereas in both systems, the HOMO, LUMO and the frontier molecular orbital energy gaps are strongly influenced by the cryptoannulenic effect