HYDROGEN-BONDING .59. NMR-STUDY OF N,N,N-TRIMETHYL-1-ADAMANTYLAMMONIUM, TRIMETHYL-I-PENTYLAMMONIUM, AND TETRA-I-PENTYLAMMONIUM IONS - AN EXPLANATION FOR THE ANOMALOUS HYDRATION BEHAVIOR OF N,N,N-TRIMETHYL-1-ADAMANTYLAMMONIUM ION SALTS

The halide and hydroxide salts of the N,N,N-trimethyl-l-adamantylammonium ion have hydration behaviors which are different from the common patterns shown by all other quaternary ammonium ion halide and hydroxide salts we have studied. These differences include formation of higher iodide and bromide hydrates, failure to form halide monohydrates, and the existence of unusual molecular ions with three-center covalent hydrogen bonding in the lower fluoride and hydroxide hydrates. The H-1 NMR spectrum of N,N,N-trimethyl-l-adamantylammonium ion is not consistent with that expected from application of conventional chemical shift rules. Comparison with the model compounds trimethyl-i-pentylammonium and tetra-i-pentylammonium ions, which have similar C-H arrangements but lack the tricyclic cage, demonstrate that through-cage interactions spread positive charge over the whole structure of the N,N,N-trimethyl-l-adamantylammonium ion. The diffusely charged nature of the ion is correlated with the observed anomalous hydration behavior of its salts.