Prototypical cyclohexane dimers: spectroscopic evidence for sigma stacking at low temperatures

摘要

Owing to the fact that sigma stacking is as important as pi stacking in determining the structural motifs of aliphatic saturated cyclic hydrocarbons, in this work we have provided the first unambiguous spectroscopic evidence for the existence of sigma stacking interactions in cyclohexane dimers at low temperatures. Molecular beam experiments performed using effusive nozzle and supersonic jet sources on cyclohexane in an N-2 matrix generated cyclohexane dimers stabilized through sigma stacking and the dimers were characterized by infrared spectroscopy. The ab initio computations carried out on cyclohexane dimers identified eclipsed (face-to-face), parallel displaced and T-shaped structures, which are predominantly stabilized by sigma stacking interactions. While natural bond orbital analysis substantiated a significant amount of sigma -> sigma* interactions involved in the stabilization, the Atoms in Molecules analysis indicated that the stacking is induced by a plausible 'dihydrogen bonding' interaction. Energy decomposition analysis disclosed that a large measure of dispersion interactions effectively contributes for the overall stability of cyclohexane dimers.