Hydrogen Bonds Seal Single-Molecule Capsules

In the presence of methanol the tetrakis(benzoxazines) complex tetramethylammonium cation within the cavity, and the cavity is completely sealed by two intramolecular hydrogen bonds between amide groups. The Cl- anion is found external to the cavity. In CHCl3, Me4N+ is complexed within the cavity, but the Cl- anion acts as a stopper in the upper rim of the cavity, hydrogen-bonded to the amide groups. The solution results are supported by single-crystal X-ray structural studies of both the single-molecule molecular capsules, and those stoppered by Cl-.