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使用MP2方法研究了N-H…O=C氢键二聚体的氢键强度,探讨了不同取代基对N-H…O=C氢键强度的影响.研究发现,可以通过改变取代基的供电性或吸电性来调控氢键强度:乙基等供电子基团对N-H…=C氢键强度的调节作用不大;-NO_2等强吸电子基团可极大地改变N-H…=C氢键强度;质子受体分子中的强吸电子基团如-NO_2可使N-H…O=C氢键强度减弱多达2.6 kcal/mol.自然键轨道(NBO)分析表明,N-H…O=C氢键强度越强,参与形成氢键的氢原子电荷越正,氧原子电荷越负,单体分子间电荷转移越多,N-H…O=C氢键中氧原子孤对电子n(O)对N-H反键轨道σ*(N-H)的二阶稳定化能越大.
The hydrogen bond strength of NH ... O = C hydrogen bond dimers was studied by using the MP2 method and the effect of different substituents on the hydrogen bond strength of NH ... O = C was discussed. It was found that by changing the chargeability or absorption Electricity to regulate the hydrogen bond strength: Ethyl and other electron-donating groups on NH ... = C hydrogen bond strength of the regulatory effect is not; -NO2 and other strong electron-withdrawing group can greatly change the NH ... = C hydrogen bond strength; Proton Strong electron-withdrawing groups such as -NO 2 in the acceptor molecule weaken the hydrogen bond strength of NH ... O = C up to 2.6 kcal / mol. The analysis of NBO shows that the stronger the NH ... O = C hydrogen bond strength , The hydrogen atoms involved in the formation of hydrogen-bonding charge more positive, the more the oxygen atom charge, the more charge transfer between the monomer molecules, NH ... O = C hydrogen bond oxygen atom lone pair of electrons n (O) to NH antibonding orbitals * (NH) second-order stabilization can be greater.