取代基对N-H…O=C氢键三聚体中氢键强度的影响

使用MP2方法研究了氢键三聚体中N—H…O=C氢键强度, 探讨了氢键受体分子中不同取代基对N—H…O=C氢键强度的影响. 研究表明, 不同取代基对氢键三聚体中N—H…O=C氢键强度的影响是不同的: 取代基为供电子基团, 氢键键长r(H…O)缩短, 氢键强度增强; 取代基为吸电子基团, 氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明, N—H…O=C氢键强度越强, 氢键中氢原子的正电荷越多, 氧原子的负电荷越多, 质子供体和受体分子间的电荷转移越多. 供电子基团使N—H…O=C氢键中氧原子的孤对电子n(O)对N—H的反键轨道滓*(N—H)的二阶相互作用稳定化能增加, 吸电子基团使这种二阶相互作用稳定化能减小. 取代基对与其相近的N—H…O=C氢键影响更大.

Effect of Substituents on Hydrogen Bonding in Strength N-H…O=C Hydrogen Bond Trimers

Theoretical calculations on a series of N—H…O=C hydrogen bond trimers were carried out using the MP2 method. We investigated the effect of substituents in hydrogen bond donor molecules on their hydrogen bond strength. The calculated results show that electron donating groups shorten the H…O distance and strengthen the N—H…O=C hydrogen bond whereas electron withdrawing groups lengthen the H…O distance and weaken the N—H…O=C hydrogen bond. Natural bond orbital (NBO) analysis further indicates that a stronger hydrogen bond in N—H…O=C results in a larger positive charge for the H atomand a larger negative charge for the O atomin the N—H…O=C bond. Natural bond orbital analysis also indicates that a stronger hydrogen bond in N—H…O=C results in a more charge transfer between the hydrogen bond donor and acceptor molecules, and results in a stronger second-order interaction energy between the oxygen lone pair and the N—H antibonding orbital. Hydrogen bonds in the N—H…O=C molecules closer to the substituent will be affected more.