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-adamantylammon ium ion have hydration behaviors which are different from the common p atterns shown by all other quaternary ammonium ion halide and hydroxid e 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 hy drogen bonding in the lower fluoride and hydroxide hydrates. The H-1 N MR spectrum of N,N,N-trimethyl-l-adamantylammonium ion is not consiste nt 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 b ut lack the tricyclic cage, demonstrate that through-cage interactions spread positive charge over the whole structure of the N,N,N-trimethy l-l-adamantylammonium ion. The diffusely charged nature of the ion is correlated with the observed anomalous hydration behavior of its salts .