The Static and Dynamic Conformational Properties of Some (1,5)-Naphthalenophanes

The Molecular Mechanics (MM) method has been applied to several dioxa-(1,5)-naphthalenophanes (1: n=14, 15, and 16, referred to as C14, C15, and C16 respectively). A systematic search, which considered many low-lying conformations, lead to the conclusion that there is no significant statistical contribution to the large negative activation entropies observed for the enantiomerization reactions of C14 and C15. Simple rules from the conformational analysis of large-ring alkanes indicated relatively few possible low energy conformations. Evaluation of the structures by MM lead to predictions about the ground state conformations of C14-C16. For C16, the [9373] conformation is predicted to be the preferred conformation, with the [8383] conformation near in energy. For C15, a class of ring expanded or contracted structures, related to higher and lower homologues, are found to be lowest in energy. Two structures, [83163] and [83712], were predicted to be the lowest in energy. For C14, the [8363] conformation is predicted to be the ground state. X-ray diffraction shows the conformation of C16 in the solid state to be [9363]. Fully refined structures were not obtained for C14 and C15 because of disorder. Therefore, a method based on 13C chemical shifts in the solid state was applied. Solid state CP-MAS 13C NMR correctly identifies the conformation of C16 as [9373]. In addition, the 13C shifts indicate the conformation of C14 to be [8363], as predicted. For C15, only the ring expanded or contracted class of conformations is consistent with the 13C NMR data. The kinetics for the jump-rope reaction of an N,N,N',N'-tetramethyldiamino-(1,5)-naphthalenophane (2) have been obtained by DNMR in D2O, CD3CN, and CD3OD. The solvent has little or no effect on the derived activation parameters. However, large differences between 2 and C14 were noted. The differences were rationalized as being due to a change in the ground state from the [8363] conformation in C14 to the [5555] conformation in 2. Finally, the kinetics of the jump-rope reaction of a gem-dimethyl substituted dioxa-(1,5)-naphthalenophane (3) were investigated. Comparison with C15 indicates no changes were induced in the activation parameters for the process.