Журнал структурной химии №4 2013 (33,55 руб.)

n. Natural bond orbital (NBO) analysis is also performed to analyze the atomic charge distribution and charge transfer in the [BMIM]+ cation and [BMIM][Ala] ionic liqui <...> s. The results show that there are the electrostatic interaction and multiple hydrogen bond interactions between the cation and the anion of the ionic liquids, and the stability of the ground state of the ion pairs mostly results from the hydrogen bonding between the lone pairs of O atoms in the anion and H in the imidazole cycle of the cati <...> s. K e y w o r d s: amino acid ionic liquids (AAILs), density functional theory (DFT), natural bond orbital (NBO), second order interaction ener <...> ]. The interaction energy ('Eint) could be used to estimate the intensity of the interaction between the cation and the anion in ion pairs, which was defined as a difference between the energy of the ion pairs and the energies of their free fragments, and it can be evaluated in Eq.(1): 'Eint = Ecation + Eanion – – Eionpair where Eionpair is the energy of the ion pairs of [BMIM][Ala], Ecation is the energy of [BMIM]+, and Eanion is the energy of [Ala <...> s. The structure of the second conformer B, which was 2.2 kJ˜mol–1 less stable than A, was very similar to that of A. The difference between these two conformers was the hydrogen bo <...> 191 Å). Compared with that of A, these hydrogen bonds of the configuration D were weak and as a result it was 33.2 kJ˜mol–1 less stable than the most stable conformer A. The other isomers of [BMIM][Ala] IL, such as E, F, and G given in Fig. 1, were 38.1 kJ˜mol–1, 46.5 kJ˜mol–1, and 50.4 kJ˜mol–1 less stable r <...> spectively. Because the acidity of C5—H in the imidazolium ring was stronger than other H of the cation unit, the hydrogen bond between the C5—H and oxygen of the anion unit must be stronger than other hydrogen bonds and contributed mostly to the stabilities of these structures of th <...> ion pairs. Therefore, the absence of the type of the hydrogen bond formed between C5—H and the oxygen atom in the isomers D, E, F, and G would reduce their stabilities relative to A, B, and C. From the above analysis, it could be concluded that in all configurations the hydr <...>