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Catenanes are playing an increasingly important role in supramolecular chemistry. In attempting to identify the minimum number of carbon atoms in a viable catenane, the B3LYP, BP86, M06-2X, MM3, and MM4 methods were applied to study representative [2]catenane models, which consist of two mechanically interlocked saturated n-cycloalkanes ([CnH2n]2). The structures, energy variations, and electron density differences vary nearly monotonically from n = 18 to 11. For example, the B3LYP/DZP++ dissociation energies [CnH2n]2 ??? 2CnH2n are 101, 121, 159, 191, 222, 252, 290, and 323 kcal/mol from n = 18 to 11, respectively. However, there is much variation among the energetic predictions with the B3LYP, BP86, M06-2X, MM3, and MM4 methods. The distances of the longest C-C single bond in each catenane are 1.593 (n = 18), 1.604 (n = 17), 1.631 (n = 16), 1.640 (n = 15), 1.667 (n = 14), 1.669 (n = 13), 1.680 (n = 12), and 1.689 ?? (n = 11). These results display something of a shoulder in the vicinity of n = 14. This may suggest that [C15H30]2 is the smallest catenane that will resist fragmentation under specified laboratory conditions.

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Feng, X.; Gu, J.; Chen, Q.; Lii, J.-H.; Allinger, N. L.; Xie, Y.; Schaefer, H. F. J. Chem. Theor. Comput. 2014, 10, 1511-1517Contributed by Steven Bachrach.Reposted from Computational Organic Chemistry with permissionHow small can a catenane be? This question...
How small can a catenane be? This question is asked by Schaefer, Allinger and colleagues and answered (well, almost answered) using computations.1 Catenanes are linked rings. The catenanes examined here are two linked saturated hydrocarbon rings, each of the...