| Autor: |
An NT; Laboratory of Computational Chemistry and Modelling (LCCM), Department of Chemistry, Faculty of Natural Sciences, Quy Nhon University, 170 An Duong Vuong Street, Quy Nhon City 590000, Vietnam. nguyentientrung@qnu.edu.vn.; Department of Computational Chemistry, J. Heyrovsky Institute of Physical Chemistry, Czech Academy of Sciences, Dolejskova 2155/3, 18223 Prague 8, Czech Republic., Vu Thi N; Laboratory of Computational Chemistry and Modelling (LCCM), Department of Chemistry, Faculty of Natural Sciences, Quy Nhon University, 170 An Duong Vuong Street, Quy Nhon City 590000, Vietnam. nguyentientrung@qnu.edu.vn., Trung NT; Laboratory of Computational Chemistry and Modelling (LCCM), Department of Chemistry, Faculty of Natural Sciences, Quy Nhon University, 170 An Duong Vuong Street, Quy Nhon City 590000, Vietnam. nguyentientrung@qnu.edu.vn. |
| Abstrakt: |
Using quantum chemical approaches, we investigated the conventional O-H⋯O and nonconventional C sp 2 -H⋯O hydrogen bonds between carboxylic acids and aldehydes in 21 stable complexes. The strength of complexes is determined by the conventional O-H⋯O bond together with the nonconventional C sp 2 -H⋯O hydrogen bond, in which the former one is 4-5 times as strong as the latter one. Proportional linear correlations of the interaction energy with both individual energies of the O-H⋯O and C sp 2 -H⋯O hydrogen bonds are proposed. Different impacts of electron-donating and electron-withdrawing groups in substituted formaldehyde and formic acid on characteristics of conventional and nonconventional hydrogen bonds, as well as the strength of both hydrogen bond types and complexes, are also evaluated. Following complexation, it is noteworthy that the largest blue shift of the C sp 2 -H stretching frequency in the C sp 2 -H⋯O bond up to 105.3 cm -1 in CH 3 CHO⋯FCOOH is due to a decisive role of the O-H⋯O hydrogen bond, which has been rarely reported in the literature. The obtained results show that the conventional O-H⋯O hydrogen bond plays a pivotal role in the significant blue shift of the C sp 2 -H stretching frequency in the nonconventional C sp 2 -H⋯O hydrogen bond. Remarkably, the considerable blue shift of the C sp 2 -H stretching frequency is found to be one H of C-H in formic acid substituted by the electron-withdrawing group and one H in formaldehyde substituted by the electron-donating group. In addition, the change in the C sp 2 -H stretching frequency following complexation is proportional to both changes of electron density in σ*(C sp 2 -H) and σ*(O-H) orbitals, in which a dominant role of σ*(O-H) versus σ*(C sp 2 -H) is observed. |
