氢键的量子化学研究(Ⅰ) 氢键类型和强度的量子化学指标

X和HY形成的氢键体系XHY,可能存在着共价形氢键X_…H-Y或离子型氢键[X-H]_…~+Y~-.区分这两种电荷的分布,量子化学计算尚有不确切之处,且对于分子内氢键的情况,无法划分XH和Y.此外,对于共价型氢键复合物还有一个稳定性问题也需要用适当的量子化学方法来衡量.     

原子间的另一种作用力——氢键

从氢键定义的延伸、键能大小及其共价性质的表现，认为氢键内容的发展已经可以将之称为"原子间的另一种作用力"。在此基础上，尝试推动氢键教学内容的改革，这样不但可以丰富基础无机化学中"氢键"的内容，而且可以有效增进学生从基础课教学提高科学研究的意识。     

多肽中氢键强度的理论研究

用B3LYP/6-31G^*法优化了多肽分子的几何构型,计算了各个构型的电荷分布和氢键酸度,进而对多肽分子中的氢键强度进行了研究.结果表明,多肽分子中氢键的强度同时取决于形成氢键的H…O原子间距R和N-H…O之间的键角β;多肽分子倾向于形成R值小、β值大的大环氢键.3₁₀螺旋结构的多肽分子中的氢键具有协同效应,分子越大,分子中氢键越多,氢键的协同效应越强.     

吡啶与HCl和CHCl3形成分子间红移氢键和蓝移氢键的理论研究

采用量子化学从头算的MP2方法, 分别在6-31G(d,p), 6-311+G(d,p)和AUG-cc-pVDZ基组下, 研究了复合物C5H5N…HCl(1), C5H5N…HCCl3(2)和C5H5N…HCCl3(3)的分子间氢键. 计算结果表明, 在复合物1中, HCl中Cl—H键伸长, 形成Cl—H…N红移氢键; 在复合物2中, HCCl3中C—H键伸长, 形成C—H…N 红移氢键; 在复合物3中, HCCl3中C—H键收缩, 形成C—H…π蓝移氢键. 自然键轨道(NBO)分析表明, 影响氢键红移和氢键蓝移主要有3个因素: n(Y)→σ*(X—H)超共轭作用、X—H键轨道再杂化和质子供体电子密度重排. 其中, 超共轭作用属于键伸长效应, 电子密度重排和轨道再杂化属于键收缩效应. 在复合物1和2中, 由于键伸长效应处于优势地位导致形成红移氢键; 在复合物3中, 由于键收缩效应处于优势地位导致形成蓝移氢键.     

关于CHF3能否形成分子间氢键的讨论

关于ＣＨＦ３能否形成分子间氢键的讨论杨秀清（新乡师范专科学校化学系河南４５３０００）由北京师范大学等三校主编的高等学校教材《无机化学》（上册）中有则习题［１］，问：ＣＨＦ３能否形成氢键？《无机及分析化学学习指导书》中的答案是ＣＨＦ３能形成分子间氢键［...     

锆元素概念的形成和发展

1789年,普鲁士分析化学家克拉普罗特提出黄锆石中含有一种新土质,并将其命名为“锆土”,锆元素假说正式形成。随后,锆的原子重量的测定以及锆元素在元素表中位置的确定,促进了锆元素假说的发展。1914年,荷兰工程师勒利和汉布格首次制得纯度较高的金属锆,这使得锆元素假说得以证实,锆元素概念正式形成。从1924年至2020年,锆同位素的发现使人们对锆元素有了新认识,促使了现代锆元素概念的形成。锆元素概念的形成和发展的过程既是元素的发现史,也是化学思想和化学方法的演进史。     

N-H…O红移氢键和蓝移氢键的理论研究

用理论方法研究了复合物HCHO…HNO, HCOOH…HNO, HCHO…NH₃, HCOOH…NH₃, HCHO…NH₂F和HCOOH…NH₂F分子间氢键. 在MP2/6-31+G(d,p), MP2/6-311++G(d,p), B3LYP/ 6-31+G(d,p)和B3LYP/6-311++G(d,p)水平上, 利用标准方法和均衡校正方法对6种复合物进行了几何优化和振动频率计算. 计算结果表明: 在复合物HCHO…HNO和HCOOH…HNO中, HNO中N—H键强烈收缩, 存在显著的N—H…O蓝移氢键. 在复合物HCHO…NH₃, HCOOH…NH₃, HCHO…NH₂F和HCOOH…NH₂F中, NH3和NH₂F中N—H键伸长, 存在N—H…O红移氢键. 利用自然键轨道(NBO)分析表明, 电子供体轨道和电子受体轨道之间相互作用的稳定化能、电子密度重排、轨道再杂化和结构重组是决定氢键红移和蓝移的主要因素. 其中, 轨道间稳定化能属于键伸长效应, 电子密度重排、轨道再杂化和结构重组属于键收缩效应. 在复合物HCHO…HNO和HCOOH…HNO中, 由于键收缩效应处于优势地位导致N—H…O蓝移氢键存在. 在复合物HCHO…NH₃, HCOOH…NH₃, HCHO…NH₂F和HCOOH…NH₂F中, 键伸长效应居于主导地位,N—H…O红移氢键出现.     

取代苯酚中共振增强的分子内氢键

根据晶体结构资料，计算了59个邻位取代苯酚中分子内氢键的几何．在STO－3G水平上计算了一些分子中原子部分电荷．结果表明，酚基氧与苯环上碳之间的键长，酚基上氢原子的部分电荷，酚基所在位置处的苯环环内角与取代苯酚的酸常数pKa均有近似线性关系，当邻位上存在硝基或羰基时，内氢键由于共振而得到显著的增强，据此可说明这一类酚的显著酸性     

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。     

On the Relationship between Hydrogen Bond Strength and the Formation Energy in Resonance-Assisted Hydrogen Bonds

Resonance-assisted hydrogen bonds (RAHB) are intramolecular contacts that are characterised by being particularly energetic. This fact is often attributed to the delocalisation of π electrons in the system. In the present article, we assess this thesis via the examination of the effect of electron-withdrawing and electron-donating groups, namely −F, −Cl, −Br, −CF₃, −N(CH₃)₂, −OCH₃, −NHCOCH₃ on the strength of the RAHB in malondialdehyde by using the Quantum Theory of Atoms in Molecules (QTAIM) and the Interacting Quantum Atoms (IQA) analyses. We show that the influence of the investigated substituents on the strength of the investigated RAHBs depends largely on its position within the π skeleton. We also examine the relationship between the formation energy of the RAHB and the hydrogen bond interaction energy as defined by the IQA method of wave function analysis. We demonstrate that these substituents can have different effects on the formation and interaction energies, casting doubts regarding the use of different parameters as indicators of the RAHB formation energies. Finally, we also demonstrate how the energy density can offer an estimation of the IQA interaction energy, and therefore of the HB strength, at a reduced computational cost for these important interactions. We expected that the results reported herein will provide a valuable understanding in the assessment of the energetics of RAHB and other intramolecular interactions.     

Mutual Weakening of Hydrogen Bonds Between Hydrogen Fluoride and Proton Donors

The mutual effect of hydrogen bonds in BHF(HHal) _n complexes (Hal = F, Cl, Br, I; B = –, CH₃CN, NH₃; n = 1-3) was examined using the self-consistent field ab initio approach (6-31++G(d,p) and ECP-HW). When two and three equivalent H bonds are formed from the lone electron pairs of the fluorine atom of the HF molecule, the mutual weakening effect is 17% and 28%, respectively. The coefficients of the mutual effects of hydrogen bonds in HF(HHal)₂ and H₂O(HHal)₂ bridges are close in magnitude.     

Theoretical Study of the Interplay between Lithium Bond and Hydrogen Bond in Complexes Involved with HLi and HCN

The lithium‐ and hydrogen‐bonded complex of HLi? NCH? NCH is studied with ab initio calculations. The optimized structure, vibrational frequencies, and binding energy are calculated at the MP2 level with 6‐311++G(2d,2p) basis set. The interplay between lithium bonding and hydrogen bonding in the complex is investigated with these properties. The effect of lithium bonding on the properties of hydrogen bonding is larger than that of hydrogen bonding on the properties of lithium bonding. In the trimer, the binding energies are increased by about 19 % and 61 % for the lithium and hydrogen bonds, respectively. A big cooperative energy (?5.50 kcal mol^?1) is observed in the complex. Both the charge transfer and induction effect due to the electrostatic interaction are responsible for the cooperativity in the trimer. The effect of HCN chain length on the lithium bonding has been considered. The natural bond orbital and atoms in molecules analyses indicate that the electrostatic force plays a main role in the lithium bonding. A many‐body interaction analysis has also been performed for HLi? (NCH)_N (N=2–5) systems.     

氢元素概念发展史与化学思想的演进

18世纪,发现氢气的卡文迪什认为该气体是水与燃素的化合物;但发现水的组成的拉瓦锡认为氢气是一种元素物质.到19世纪,原子分子论形成后,氢气被认为是由双原子分子构成的单质.20世纪30年代,氢同位素的发现使人们对氢元素概念有了新认识,并逐渐形成现代氢元素概念.氢元素概念的发展史不仅是元素概念的发展史,也是科学思想的演进史...     

纯水溶液中的氢键交换反应路径

利用分子动力学模拟方法对纯水溶液的氢键转化动力学性质进行了深入的微观探讨,溶液中非氢键构型为寿命较短(0.1～0.2 ps)的过渡态构型,我们发现氢键交换通过两种过渡构型完成,氢键角度扭曲激发后与氢键第一壳层水分子沿路径1交换,氢键径向拉伸激发后与氢键第二壳层水分子沿路径2交换,过渡态路径的选择具有温度依赖性.氢键转化需在旧氢键受体氢键过量和新氢键受体氢键不足,同时满足交换反应空间结构要求下才能完成.氢键交换反应对水分子平动和转动行为起着决定作用.     

Analysis of Proton NMR in Hydrogen Bonds in Terms of Lone‐Pair and Bond Orbital Contributions

NMR spectroscopic parameters of the proton involved in hydrogen bonding are studied theoretically. The set of molecules includes systems with internal resonance‐assisted hydrogen bonds, internal hydrogen bonds but no resonance stabilization, the acetic acid dimer (AAD), a DNA base pair, and the hydrogen succinate anion (HSA). Ethanol and guanine represent reference molecules without hydrogen bonding. The calculations are based on zero‐point vibrationally averaged molecular structures in order to include anharmonicity effects in the NMR parameters. An analysis of the calculated NMR shielding and J‐coupling is performed in terms of “chemist’s orbitals”, that is, localized molecular orbitals (LMOs) representing lone‐pairs, atomic cores, and bonds. The LMO analysis associates some of the strong de‐shielding of the protons in resonance‐assisted hydrogen bonds with delocalization involving the π‐backbone. Resonance is also shown to be an important factor causing de‐shielding of the OH protons for AAD and HSA, but not for the DNA base pair. Nitromalonamide (NMA) and HSA have particularly strong hydrogen bonds exhibiting signs of covalency in the associated J‐couplings. The analysis results show how NMR spectroscopic parameters that are characteristic for hydrogen bonded protons are influenced by the geometry and degree of covalency of the hydrogen bond as well as intra‐ and intermolecular resonance.     

Protonation Switching to the Least‐Basic Heteroatom of Carbamate through Cationic Hydrogen Bonding Promotes the Formation of Isocyanate Cations

We found that phenethylcarbamates that bear ortho‐salicylate as an ether group (carbamoyl salicylates) dramatically accelerate O?C bond dissociation in strong acid to facilitate generation of isocyanate cation (N‐protonated isocyanates), which undergo subsequent intramolecular aromatic electrophilic cyclization to give dihydroisoquinolones. To generate isocyanate cations from carbamates in acidic media as electrophiles for aromatic substitution, protonation at the ether oxygen, the least basic heteroatom, is essential to promote C?O bond cleavage. However, the carbonyl oxygen of carbamates, the most basic site, is protonated exclusively in strong acids. We found that the protonation site can be shifted to an alternative basic atom by linking methyl salicylate to the ether oxygen of carbamate. The methyl ester oxygen ortho to the phenolic (ether) oxygen of salicylate is as basic as the carbamate carbonyl oxygen, and we found that monoprotonation at the methyl ester oxygen in strong acid resulted in the formation of an intramolecular cationic hydrogen bond (>C?O⁺?H???O<) with the phenolic ether oxygen. This facilitates O?C bond dissociation of phenethylcarbamates, thereby promoting isocyanate cation formation. In contrast, superacid‐mediated diprotonation at the methyl ester oxygen of the salicylate and the carbonyl oxygen of the carbamate afforded a rather stable dication, which did not readily undergo C?O bond dissociation. This is an unprecedented and unknown case in which the monocation has greater reactivity than the dication.     

CH3SH与HOCl分子间氢键和卤键的结构与性质

在DFT-B3LYP及MP2/6-311＋＋G**水平上分别求得CH3SH…HOCl氢键复合物和CH3SH…ClOH卤键复合物势能面上的稳定构型. 频率分析表明, 与单体HOCl相比, 在两种复合物中, Cl(9)—O(7)和H(8)—O(7)键伸缩振动频率发生显著的红移. 经MP2/6-311＋＋G**水平计算的含基组重叠误差(BSSE)校正的气相中相互作用能分别为－19.23和－6.85 kJ&#8226;mol－1. 自然键轨道理论(NBO)分析表明, 在CH3SH…ClOH卤键复合物中, 引起Cl(9)—O(7)键变长的因素包括2种电荷转移: (i)孤对电子LP[S(1)]1→σ*[Cl(9)—O(7)]; (ii)孤对电子LP[S(1)]2→σ*[Cl(9)—O(7)], 其中孤对电子LP[S(1)]2→σ*[Cl(9)—O(7)]转移占主要作用, 总的结果是使σ*[Cl(10)—O(11)]的自然布居数增加, 同时O(7)和Cl(9)原子s成分均增加的杂化重优具有与电荷转移作用相同的“拉长效应”; 在CH3SH…HOCl氢键复合物中也存在类似的电荷转移, 但是O(7)原子的再杂化效应不同于前者. 自然键共振理论(NRT)进行键序分析表明, 在氢键复合物和卤键复合物中, H(8)—O(7)和Cl(9)—O(7)键的键序都减小. 通过分子中原子理论(AIM)分析了复合物中氢键和卤键的电子密度拓扑性质.     

Molecular Tailoring Approach for the Estimation of Intramolecular Hydrogen Bond Energy

Hydrogen bonds (HBs) play a crucial role in many physicochemical and biological processes. Theoretical methods can reliably estimate the intermolecular HB energies. However, the methods for the quantification of intramolecular HB (IHB) energy available in the literature are mostly empirical or indirect and limited only to evaluating the energy of a single HB. During the past decade, the authors have developed a direct procedure for the IHB energy estimation based on the molecular tailoring approach (MTA), a fragmentation method. This MTA-based method can yield a reliable estimate of individual IHB energy in a system containing multiple H-bonds. After explaining and illustrating the methodology of MTA, we present its use for the IHB energy estimation in molecules and clusters. We also discuss the use of this method by other researchers as a standard, state-of-the-art method for estimating IHB energy as well as those of other noncovalent interactions.