The Influences Of Hydrogen Bonds On The Amido Bond And Pnicogen Bond Or Chalcogen Bond In H₂XP…SHY Complexes

In this paper, the related calculation methods and analysis means by quantum chemistry are employed to investigate the characteristics of pnicogen bonds and chalcogen bonds formed in H2XP-SHY(X, Y=H, F, Cl, Br) complexes, and the influences of substituents X and Y on the bonds. Analyzed the influences of N…H-X and O…H-X (X= F, Cl, Br, CN, OH, OCH3) intermolecular hydrogen bonds on the amido bond in acetamide. We discussed the effects of N…H-X (X=F, Cl, Br, COOH) hydrogen bonds on the 3c-4e delocalized Ï€(N-C=O) bond in formamide and FCONH2. So there are three parts in the following:1. Ab initio quantum chemistry methods MP2 and CCSD(T) are applied to study the essential properties of pnicogen bonds X-P…S and chalcogen bonds Y-S…P formed in PH2X-SHY(X, Y=H, F, Cl, Br)complexes, and focused on the change of pnicogen bonds and chalcogen bonds with substituents X and Y. Calculated results show that the chalcogen bonds are stronger than the pnicogen bonds, the substituents with larger electronegativity connected with the Lewis acid will strengthen the bonds and make large effects on the structures and properties of the monomers, but the substituents linked to the Lewis bases produce opposite effects. The energies of chalcogen bonds are 2.0-5.6 kcal/mol, and the strongest chalcogen bond is found in the strcuture HFS…PH3 with bonding energy 3.83 kcal/mol by CCSD(T) method. The energies of pnicogen bonds are 1.8-3.5 kcal/mol. and the strongest pnicogen bond is found in H2FP…SH2 with CCSD(T) bonding energy 2.99 kcal/mol.2. Ab initio quantum chemistry methods are applied to study the hydrogen bonds between acetamide and the proton donors HX(X= F, Cl, Br, CN, OH, OCH3) and observe their effects on the amido bond -CO-NH-. We found that there are two types of hydrogen bonds N…H-X and O…H-X, but they have completely opposite effects on the amido bond. The N…H-X H-bonds weakens the 3c-4e delocalized Ï€(N-C=O) bond and elongates the C-N bonds, but shortens the C=O bond. While the O…H-X H-bonds produce opposite effects. These different effects of the two types of H-bonds are caused by their different mechanisms, which involve the competition and coupling between intermolecular hyperconjugations Lp(N) or Lp(O) to σ*(HX) and intramolecular hyperconjugations Lp(N) to Ï€*(C=O) and Lp(O)â†'σ*(CN). The interaction energies of the two types of H-bonds are larger, and the energies of the O-H-X H-bonds are twice as large as the corresponding N-H-X H-bonds. All those H-bonds are red-shifted.3. The intermolecular hydrogen bonds N…H-X(X-F, Cl, Br, COOH) between formamide. FCONH2 and HX have been theoretically studied by the M(?)ller-Plesset method MP2, and discussed the effects of N…H-X hydrogen bonds on the 3c-4e delocalized Ï€(N-C=O) bond in formamide and FCONH2. In the FCONH2 monomer, the formation of 3c-4e delocalized Ï€(F-C=O) bond causes the electron density of C-N, C=O and 3c-4e(N-C=O)Ï€ bond increase, so the energies of those bonds enhanced. What is more, the other 3c-4e delocalized Ï€(F-C=O) bond decreased the strengths of N…H-X hydrogen bonds, and protect the 3c-4e delocalized Ï€(N-C=O) bonds are not destroyed by the N…H-X hydrogen bonds.