Origin of co-conformational selectivity in a [3]rotaxane.

Co-conformational selectivity and structure-energy relationships in a [3]rotaxane are investigated with a recently developed multiple-sampling and statistical analysis procedure for modeling interlocked molecules and mechanical molecular devices. The results presented confirm the experimentally observed co-conformational selectivity. The theoretical calculations reveal that ring-ring interactions are very small and ring-shaft inter-component interactions decide the co-conformational preference. In particular, it is found that stronger ring binding at the central binding station on the shaft than at either of the two terminal binding stations gives rise to the observed co-conformational preference. Analysis of radius of gyration data shows that co-conformational isomerism is not strongly correlated to coiling of the shaft.