Behavior of Multi-HBs in Acetic Acid Dimer and Related Species: QTAIM Dual Functional Analysis Employing Perturbed Structures Generated Using Coordinates from Compliance Force Constants

The dynamic and static nature of each hydrogen bond (HB) in acetic acid dimer (1), acetamide dimer (2a), thio- and seleno-derivatives of 2a (2b and 2c, respectively), and acetic acid–acetamide mixed dimer (3) was elucidated with QTAIM dual functional analysis (QTAIM-DFA). Such multi-HBs will form in 1–3, in close proximity in space, and interact mutually and strongly with each other. Perturbed structures generated using coordinates derived from the compliance force constants (Cij: the method being called CIV) are employed in QTAIM-DFA, for the establishment of the methodology to elucidate the nature of each HB in the multi-HBs. The dynamic nature of interactions with CIV is described as the “intrinsic dynamic nature of interactions”, since the coordinates corresponding to Cij are invariant to the choice of the coordinate system. Each HB in the multi-HBs of 1–3 are predicted to have the nature of CT-MC (molecular complex formation through charge transfer) appear at the regular closed shell region, which are stronger than each HB of the isomers of 1–3. The methodology to elucidate the nature of multi-HBs is well established, which employs the perturbed structures generated with CIV for QTAIM-DFA.