Theoretical Study on the Rearrangement between the Isomers of C60X (X = O and S)

Abstract

The rearrangements between the closed [6,6] and open [5,6] isomers of C 6 0 O, as well as the closed [6,6], closed [5,6], and open [5,6] isomers of C 6 0 S have been studied using semiempirical AM I and MNDO methods. The results show that the interconversion of the two isomers of C 6 0 O follows a two-step pathway involving an intermediate and two transition states. The calculated activation barriers for the migration of oxygen from [6,6]-bond to [5,6]-bond through an intermediate are 189.1 and 54.6 kJ mol - 1 , respectively. In the opposite way, the calculated activation barriers for the migration of oxygen from [5,6]-bond to [6,6]-bond through an intermediate are 293.2 and 2.7 kJ mol - 1 , respectively. The interconversion of the closed [6,6] and the open [5,6] isomers of C 6 0 S also follows a stepwise pathway via a local energy minimum corresponding to the closed [5,6] isomer. The calculated activation barriers for the migration of sulfur from [6,6]-bond to [5,6]-bond (in open [5,6] isomer) through the closed [5,6] isomer are 233.2 and 1.2 kJ mol - 1 , respectively. In the opposite way, the calculated activation barriers for the migration of sulfur from [5,6]-bond (in open [5,6] isomer) to [6,6]-bond via the closed [5,6] isomer are 82.0 and 150.5 kJ mol - 1 , respectively. The large barriers suggested that it should be possible to isolate the closed [6,6] and open [5,6] isomers of C 6 0 O at room temperature. This is consistent with experimental results. In addition, it can be inferred from our results that rearrangement between the two isomers of C 6 0 O can take place under heating or lighting conditions. Meanwhile, it can be deduced from our results that it should be possible to isolate both the closed [6,6] and the open [5,6] isomers of C 6 0 S at room temperature and to convert one into the other when certain energy is offered. It seems that the closed [5,6] isomer of C 6 0 S may not be observed experimentally at room temperature.