Non covalent interactions in the monohydrated complexes of 1,2,3,4 –tetrahydroisoquinoline in S 0

Abstract

Abstract The eleven monohydrates of 1, 2, 3, 4-tetrahydroisoquinoline (THIQ) are analysed through Natural Bond Orbital (NBO) analysis and QTAIM methods employing M06-2X functional in DFT and MP2 methods. Here, the role of OH bonds as an acceptor and donor are critically analyzed. The role of O lone pairs is critically monitored in two of the complexes, where N-H···O hydrogen bonds are present. The relative contributions of rehybridisation and hyperconjugation are compared in detail. Popellier criteria are satisfied in all the complexes involving strong hydrogen bonds. Strong hydrogen bonding is observed among four complexes. These are confirmed through the negative values of total electron energy density (HC), while Laplacian \({(\nabla }^{2}{{\rho }}_{\text{C}} )\)remains positive at the bond critical points (BCP). All these are O-H⋅⋅⋅N type bonds. Remaining h-bonds are weaker in nature. These are also confirmed by the smaller values of electron density ρC at the BCP. The variation of potential energy density (VC) among the complexes seems to be the most important factor in determining the nature of non-covalent interactions.