AM1, MNDO and MINDO/3 treatments of Huckel type cyclacenes

Huckel type cyclacenes having R = 3-10 have been subjected to quantum chemical analyses at the level of AM1, MNDO and MINDO/3 (UHF and RHF) type semi-empirical treatments. The structures have been found to be stable but endothermic in nature. No cryptoannulenic effect has been observed when AM1 (UHF) and MNDO (UHF) treatments are used. Whereas MINDO/3 (UHF) and all the RHF type calculations indicated certain degree of cryptoannulenic effect R = 4 through 8 for the heat of formation values. Frontier molecular orbital energies of the systems have also been reported