Theoretical investigation on the improper hydrogen bond in κ-carrabiose⋯Y (Y = HF, HCl, HBr, NH₃, H₂O, and H₂S) complexes

International audienceThe nature of H-bonds in κ-carrabiose⋯Y (Y = HF, HCl, HBr, NH3, H2O, and H2S) complexes was studied. For this aim, the structure of isolated κ-carrabiose was optimized using three global hybrids functional: B3LYP, PBE0, and M06-2X combined with 6-311G** basis set. Subsequently, the κ-carrabiose in the presence of HF, HCl, HBr, NH3, H2O, and H2S was optimized using the CBS-4 M method. NBO analyses were then carried out at the MP2/6-311G** level of theory. A particular interest was focused on C(18)―H(34)⋯Y bond. The results reveal that the C(18)―H(34)⋯Y bond is an improper H-bond since a significant contraction of C(18)―H(34) was observed during the complexation leading to a significant blueshifted stretching frequency. The NBO analyses have shown that the formation of the improper H-bonds C(18)―H(34)⋯Y (Y = F, Cl, Br, N, O, and S) is principally due to the increase of the s-character of the hybrid orbital in carbon atom (rehybridization) in κ-carrabiose⋯Y complexes. Regarding the polarization, it was proved that more the H-bond center (carbon in C(18)―H(34)⋯Y) becomes less positive, the hydrogen more positive, and Y more negative; more the contraction of the C(18)―H(34) bond is important. It was also confirmed for intramolecular H-bonds in κ-carrabiose⋯Y complexes that the rehybridization is responsible for H-bonds nature either proper or improper

Testing the CP-correction procedure with different DFT methods on H-bonding complexes of κ-carrabiose with water molecules

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Theoretical Study on Non-Linear Optics Properties of Polycyclic Aromatic Hydrocarbons and the Effect of Their Intercalation with Carbon Nanotubes

Results of a theoretical study devoted to comparing NLO (non-linear optics) responses of derivatives of tetracene, isochrysene, and pyrene are reported. The static hyperpolarizability β, the dipole moment μ, the HOMO and LUMO orbitals, and their energy gap were calculated using the CAM-B3LYP density functional combined with the cc-pVDZ basis set. The para-disubstituted NO2-tetracene-N(CH3)2 has the highest NLO response, which is related to a large intramolecular charge transfer. Adding vinyl groups to the para-disubstituted NO2-tetracene-N(CH3)2 results in an increase in the NLO responses. We further investigated the effect of the intercalation of various push–pull molecules inside an armchair single-walled carbon nanotube. The intercalation leads to increased NLO responses, something that depends critically on the position of the guest molecule and/or on functionalization of the nanotube by donor and attractor groups

Rationalizing aggregate structures with orbital contributions to the exchange-repulsion energy

It is shown that repulsive interactions have a crucial influence on the structure of prototypical non-covalently bonded systems. To explain this, we propose a molecular orbital based model for the exchange-repulsion contribution to the total interaction energy. As a central result, our model shows that energetically preferred aggregate structures exhibit reduced exchange repulsion, which can be deduced from the nodal structure of certain occupied orbitals. In this way, the directionality of halogen bonds and the preferred arrangements in pi-aggregates are explained using the Cl2-He, benzene-benzene, and benzene-hexafluorobenzene systems as examples, where commonly applied electrostatic models fail

Density functional conformational study of 2‐O‐sulfated 3,6 anhydro‐α‐D‐galactose and of neo‐κ‐ and ι‐carrabiose molecules in gas phase and water

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