Assessing the Attractive/Repulsive Force Balance in Axial Cyclohexane C-H-ax center dot center dot center dot Y-ax Contacts: A Combined Computational Analysis in Monosubstituted Cyclohexanes

作者：Lopez Carlos Silva; Faza Olalla Nieto; De Proft Frank; Kolocouris Antonios^*

来源：Journal of Computational Chemistry, 2016, 37(30): 2647-2658.

DOI：10.1002/jcc.24496

• axial cyclohexane contacts
• NBO
• QTAIM
• Weizsacker kinetic energy
• Grimme's dispersion correction
• attractive forces
• non-covalent interactions

The interactions of axial substituents in monosubstituted cyclohexane rings are studied in this work using an array of different computational techniques. Additionally, the anomalous axial preference for some bulky substituents is related to stabilizing dispersion interactions. We find that the C-H-ax center dot center dot center dot Y-ax contacts for various substituents with distances ranging from 2 to similar to 5 angstrom may include attractive dispersion forces that can affect the conformational equilibrium; these forces co-exist with Pauli repulsive forces effected by Y-ax group due to van der Waals sphere penetration. At distances between 2 and 3 angstrom stabilizing electron transfer interactions were calculated and the combination of natural bond orbital and QTAIM analysis showed that, in certain cases, Y-ax=Bu-t, C-ax-O or C-ax=O or S-ax=O or C-ax=S this interaction can be characterized as an improper H-bond. DFT-D3 and non-covalent interactions calculations (NCIs) in cyclohexane derivatives with Y-ax=SiOR3 including H-Yax center dot center dot center dot H-cy surfaces at distances ranging between 4 and 6 angstrom suggest that dispersion has a clear effect on the experimentally observed stabilization of the axial conformer. NCIs computed from the reduced density gradient help to visually identify and analyze these interactions.

• 出版日期2016-11-15