trans- versus cis-1,3,5,7-Tetraoxadecalin:  A Structural, Thermochemical, and Computational Study¹a

In a multidisciplinary study (low-temperature X-ray diffraction, heats of combustion, and high-level (MP2/6-31+G*) ab initio calculations), the structure and relative stability of trans -1,3,5,7-tetraoxadecalin ( 1 ) versus its cis -diastereomer ( 2 ) were established. We also calculated the atomic charges and proton affinities of the oxygen sites to predict the probable coordination sites in each isomer. Excellent agreement was found between the experimental and theoretical structural parameters, which were well reproduced by force field calculations using MM3-GE (MM3 reparametrized for the gauche effect). Also, 1 and 2 are largely equienergetic within experimental errors and the computational methods used.