Potential energy surface describing spindle rotation in a molecular turnstile

The shape of the potential energy surface which describes the spindle rotation in the phenylacetylene macrocycle 1 and the nature of the transition state through which the "turnstile" passes was studied for a series of substituents (X = H, F, Cl, CN, CH3, OCH3, CH2OCH3). Semiempirical molecular orbital calculations were carried out employing the PM3 method of program package Mopac. The shape of the macrocycle and the barrier to spindle rotation are also reported. (C) 1999 Elsevier Science B.V. All rights reserved.