DFT和热力学研究氢键协同效应及对关联1H NMR的影响

用DFT方法在B3LYP／6—311 G(d，p)水平下研究了甲醇线性和环状分子簇．对于不同大小的分子簇之间定义了协同因子，计算得到的协同因子可以验证氢键的强协同效应，环状分子簇之间的协同效应远远大于线性分子簇，做为理论验证和比较，热力学模型分别采用含氢键缔合的格子流体状态方程(LFHB)，以及含氢键协同效应的LFHB，关联醇一惰性体系的^1H核磁共振化学位移．考虑协同效应的关联结果优于原始的LFHB，比较量子化学计算的和热力学模型中采用的协同因子，认为甲醇和乙醇在溶液中更可能大部分以线性缔合形式存在。

DFT and Thermodynamic Studies on Hydrogen Bond Cooperativity and Its Effects on the 1H NMR Correlation

In this paper systematic DFT calculations were carried out to study hydrogen bond cooperativity of linear and cyclic clusters consisting of up to 5 molecules of methanol at B3LYP/6-311++G (d,p) level. A definition has been proposed for cooperative factor for clusters of different size. Calculated cooperative factors are far greater for cyclic clusters than for linear ones. For comparison, LFHB model (the lattice-fluid hydrogen-bonding equation of state model) with or without cooperative effects was used to fit the 1H NMR chemical shift data of (methanol or ethanol+inert solvent) mixtures. More satisfactory results were obtained by including the cooperative effects in the thermodynamic model. Comparing the calculated cooperative factors with those used in cooperative LFHB, liquid methanol could be considered to exist mostly as linear clusters.