Chemistry and structure of diterpenes of the Kaurane series: III. Molecular H complex of isosteviol with aniline

Individual molecular H complex of isosteviol with aniline (2 : 1) was isola ted. The aniline NH2 group plays the role of proton donor and the isostevio l carboxy group, acts as proton acceptor. Isosteviol molecules bound to ani line molecules form double helices about the 4(3) chiral axis. In their tur n, these helices are bound to each other by hydrogen bonds between isostevi ol molecules of neighboring helices, thus forming a supramolecular crystal structure of the complex. The enthalpies of formation of the hydrogen bonds in the complex were estimated. In CCl4 solutions the complexes are in equi librium with acid isosteviol dimers, their associates with aniline, as well as free isosteviol and aniline molecules.