Synthesis and structure of, and bonding in some derivatives of 2,6,9,10-tetraoxatricyclo[3.3.1.13,8]-decane.

Five derivatives of 2,6,9,10-tetraoxatricyclo[3.3.1.1^3,8]decane were synthesized and their molecular structures in the solid state were determined by means of X-ray diffraction analysis. In addition, the structure of all the molecules were optimized at different levels of computational quantum chemistry (HF/6-31G*, B3LYP/6-31G*). Experimentally determined bond lengths were compared with their calculated counterparts, and striking differences between the Hartree-Fock (HF) results and the experimental data could be traced back to the lack of correlation energy in the geometry optimizations. Two of the compounds under consideration are diastereomers and their relative stability was not only calculated with a conventional ab inito method (ZPE+MP2/6-31G*//HF/6-31G*), but also within the framework of density functional theory (B3LYP/6-31G*). In some of the calculations the influence of the solvent was included in single point calculations by means of an electrostatic model. Moreover, combining experimental as well as computational results, the exclusive axial orientation of a Cl atom in one of the compounds could be explained by an interplay of kinetic and energetic effects.