The Influence of Homoring Competition Effect of Substituents on the Nonclassical Hydrogen Bonding Properties in Diarylnitroketone

Abstract

Nonclassical hydrogen bond (NCHB) as a weak interaction force not only plays an important role in organic conversion and catalysis but also has significant implications for understanding and predicting the properties of compounds. At present, the influence of homoring competition effect of substituents on the intramolecular properties of NCHB has not been studied. In this work, 51 diphenylnitroketone XArCH=N(O)ArY (XPNY) compounds containing different substituents were chosen as model molecules, the bond energy (E_HB) in CH⋯O and aromaticity of quasi-aromatic ring (PDI_Q) were computed, and the chemical shifts δ_H(CH⋯O) of ¹H NMR in CH⋯O were collected or measured. This work focuses on analyzing the NCHB CH⋯O hydrogen bond in compounds XPNY and explored the influence of homoring competition effect of substituents on the energy E_HB of CH⋯O and chemical shift value δ_H(CH⋯O). The results show that (1) the chemical shift values δ_H(CH⋯O) of CH⋯O in XPNY are abnormally large, and the values of E_HB are 14.15–15.51 kJ/mol, lower than 16.74 kJ/mol, which is consistent with the characteristics of intramolecular NCHB. Therefore, it can be considered that the CH⋯O hydrogen bonds are NCHB in XPNY. (2) The substituent X in compound XPNY exhibits the homoring competition effect. (3) The aromaticity of quasi-aromatic ring Q is the main factor affecting the E_HB. The substituent X affects the E_HB and δ_H(CH⋯O) along different paths. This study can help understanding the impact of substituent effects on NCHB in depth.