碳氟键均裂解离能的密度泛函理论研究

运用6种密度泛函方法(B3LYP, B3P86, B3PW91, PBE1PBE, MPW1B95, MPW1K)对15个含氟有机化合物的碳氟键均裂解离能进行理论计算, 得到的理论值与实验值比较, 发现B3P86方法用于碳氟键均裂解离能的计算相对可靠. 使用验证后的理论方法对含氟杂环有机化合物和卤氟烃中的碳氟键均裂解离能进行了预测和分析, 并进一步讨论了α-取代基效应以及Hammett型取代基效应对碳氟键均裂解离能的影响.     

环境污染物中碳氯键离解能的理论研究

利用六种密度泛函理论方法（B3LYP, B3P86, MPW1K, TPSS1KCIS, X3LYP, BMK）对碳氯键离解能进行理论计算,结果发现几种新发展的密度泛函(DFT)方法用于碳氯键离解能的计算比传统的B3LYP有较大的改善,其中对能量估算相对准确的B3P86方法对碳氯键离解能的计算精度最高,对17个分子中碳氯键离解能计算的平均绝对偏差为6.58 kJ/mol。最后运用B3P86方法对一系列环境危害较大,但可通过光化学降解和生物降解的氯代有机物的碳氯键离解能值进行预测,并讨论了影响碳氯键离解能的结构性质关系。     

DFT Study on Homolytic Dissociation Enthalpies of C-I Bonds

The C-I bond dissociation enthalpies （BDE） of various organic iodides were calculated using high-level theoretical methods including MP2 and CCSD（T） with extrapolated basis set as well as a number of density functional theory methods. After systematic evaluation of the theoretical results against available experimental C-I BDEs, it was found that the MPW LYPIM method gave the lowest root mean square error. We, therefore, used this method to examine the substituent effects on different categories of C（sp3）-I and C（sp2）-I bonds. Fur thermore, the remote substituent effects on the C-I BDEs of substituted iodobenzenes and substituted （iodomethyl）benzenes were also investigated at the same level. The C-I BDEs of typical heteroaromatic iodides including five-membered and six-membered heterocyclic iodides were also examined.     

烃类化合物碳氢键解离焓的密度泛函理论研究

通过比较10种密度泛函方法对烃类化合物碳氢键解离焓的计算精度, 发现新型密度泛函BMK方法具有最高的计算精度. 利用该方法计算了包含饱和链烃,、不饱和链烃、脂环烃和芳香烃在内的172个烃类化合物的碳氢键解离焓,计算均方根误差仅为7.95 kJ•mol^－1, 线性拟合常数为0.985. 通过自然键轨道法分析发现, 烃类物质的碳氢键解离焓与母体的碳氢键杂化轨道成分p%, 自由基奇电子轨道杂化成分p%及自由基的自旋密度三个参数之间存在较好的定量关系. 此外, 饱和链烷烃及不饱和链烃的碳氢键解离焓与碳氢键键长之间也存在较好的线性关系.     

关于键解离能、键能、反应焓变的探讨

键解离能、键能、反应焓变是广泛应用的化学术语,也是中学化学教学中容易混淆的概念。通过探讨3者的联系及区别,以期让教师形成清晰认识,从而在教学实践中加以准确应用。     

卤代甲烷的键离解能与取代基效应

将芳环上取代基的电子效应参数引入卤代甲烷, 以卤代甲烷分子Y-CH_nX_{3－n (n＝0～3; Y＝H, F, Cl, Br, I; X＝F, Cl, Br, I)中Y-C键的标准键焓 与中心C原子相键连原子的场/诱导效应之和ΣFi、共轭效应之和ΣRi以及诱导偶极之和Σ(α×F)为参数, 建立了一个定量估算卤代甲烷分子中Y-C键离解能(BDE)的通用模型, BDE(Y-C)＝57.5460＋0.8855 －101.0780ΣRi－64.8390ΣFi－10.1034Σ(α×F). 对35个C-H, C-F, C-Cl, C-Br和C-I键回归分析结果表明, 估算Y-C键离解能的精度在实验误差范围内. 对外部数据集的预测结果表明, 该模型具有较高的预测精度, 可用于预测还没被实验测定的卤甲烷中Y-C键离解能. 还对卤代甲烷中104个C-Y键的键离解能进行了预测. 将芳环上取代基效应用于研究饱和体系化学键性能, 有利于深入理解取代基效应对化学键性能的影响.}     

高位阻烷烃的C-C和C-H键的键离解能

本文使用ONIOM-G3B3的方法计算了一系列高位阻烷烃的C-C和C-H键离解能。研究还测定了它们的几何参数,如键长,键角,分子体积等,它们中的绝大多数分子目前还没有被合成。这些几何参数表征了位阻效应对键离解能产生的影响。研究确定了键离解能的迅速减小和分子体积的增大之间的一些关系。这些关系可以帮助使用理论方法预测很多高位阻化合物的合成。     

N—O键解离焓的密度泛函理论研究

在高精度计算方法G3和G3B3的基础上,比较了密度泛函理论(DFT)十几种方法对N—O键解离焓(BDE)相对于实验值的计算精度,发现用B3P86方法计算15种化合物N—O键的BDE,均方根误差最小,仅为6.36kJ·mol-1,计算值与实验值的线性相关系数为0.991.在此基础上,用该方法分别计算了非芳香化合物及芳香化合物的N—O键BDE.通过自然键轨道分析,发现部分N—O键的BDE与N—O键的键长、原子电荷密度及键级之间存在定量关系.此外,在B3P86方法的基础上预测了几种典型的杂环芳香化合物N—O键BDE值.     

Surprising Homolytic Gas Phase Co−C Bond Dissociation Energies of Organometallic Aryl-Cobinamides Reveal Notable Non-Bonded Intramolecular Interactions

Aryl-cobalamins are a new class of organometallic structural mimics of vitamin B₁₂ designed as potential ‘antivitamins B₁₂’. Here, the first cationic aryl-cobinamides are described, which were synthesized using the newly developed diaryl-iodonium method. The aryl-cobinamides were obtained as pairs of organometallic coordination isomers, the stereo-structure of which was unambiguously assigned based on homo- and heteronuclear NMR spectra. The availability of isomers with axial attachment of the aryl group, either at the ‘beta’ or at the ‘alpha’ face of the cobalt-center allowed for an unprecedented comparison of the organometallic reactivity of such pairs. The homolytic gas-phase bond dissociation energies (BDEs) of the coordination-isomeric phenyl- and 4-ethylphenyl-cobinamides were determined by ESI-MS threshold CID experiments, furnishing (Co−C )-BDEs of 38.4 and 40.6 kcal mol⁻¹, respectively, for the two β-isomers, and the larger BDEs of 46.6 and 43.8 kcal mol⁻¹ for the corresponding α-isomers. Surprisingly, the observed (Co−C )-BDEs of the Co_β-aryl-cobinamides were smaller than the (Co−C )-BDE of Co_β-methyl-cobinamide. DFT studies and the magnitudes of the experimental (Co−C )-BDEs revealed relevant contributions of non-bonded interactions in aryl-cobinamides, notably steric strain between the aryl and the cobalt-corrin moieties and non-bonded interactions with and among the peripheral sidechains.     

取代基效应对褐煤模型化合物离解焓影响的理论研究

为了探究褐煤热解过程中氧桥键C-O均裂这一重要反应, 选取α-O-4和β-O-4类结构单元作为褐煤模型化合物, 运用不同密度泛函计算了部分模型化合物中C-O的离解焓, 并以CBS-QB3作为理论基准值进行比较, 最后选取M05-2X进行离解焓计算. 结果显示, 对于选定的α-O-4和β-O-4类模型化合物, 其平均离解焓分别为51.0 kcal/mol和66.1 kcal/mol. 周围取代环境能显著影响C-O离解焓, 芳环上存在给电子基团(OH, OCH₃和CH₃)能降低C-O离解焓, 而吸电子基团COOH则能增加其离解焓. 然后深层次分析了取代基效应对C-O离解焓的影响. 此外, 分子内氢键的形成对离解焓也有很大的影响. C-O的离解焓与其键长没有特定的相关性, 不能简单的通过C-O键长来预测其离解焓.     

Accurate Prediction of IrH Bond Dissociation Enthalpies by Density Functional Theory Methods

The iridium hydride complexes have been extensively used in organic reactions, such as oxidation and hydrogenation reactions. In many of these reactions, the dissociation or formation of Ir? H bond plays an important role in determining the overall reaction rates and yields. In the present study, the accuracy of different theoretical methods for prediction of Ir? H bond strengths has been examined on the basis of the previously reported Ir? H BDEs of 17 different complexes. Comparing the performance of different DFT functionals (e.g. B3LYP, TPSS, M06), different basis sets (including the different effective core potentials (ECP) on Ir and I atoms, and the total electron basis sets on the other atoms), and different solvation models (SMD, CPCM, and IEFPCM) in solution phase single point calculations, we found that the gas‐phase calculation with TPSS/(LanL2DZ: 6‐31G(d)) method is relatively more accurate than the other gas‐phase calculation methods, and can well simulate the Ir? H BDEs in low‐polarity solvents (such as chlorobenzene and dichloroethane). Finally, efforts were put in analyzing the structure‐activity relationships between the ligand structure (around Ir center) and the Ir? H BDEs. We wish the present study could benefit future studies on the Ir‐H complexes involved organic reactions.     

密度泛函法计算C1-C14正构烃生成焓及C-C键裂解能

采用密度泛函理论(DFT)方法研究了费托石脑油裂解反应中涉及到C₁-C₁₄正构烃和自由基中间体的生成焓及其C-C键解离能(BDE)。 结果表明,在所有评价的密度泛函理论方法（B97-1、BB1K、B1B95、MPWB1K和MPW1B95）中,MPW1B95/6-311G(d,p)方法计算最精确。 以此方法为基准,进一步对高碳烃及其裂解产物的标准生成焓和C-C键解离能进行了预测。 与可得到的实验数据相比,MPW1B95/6-311G(d,p)方法预测的烃和自由基的平均生成焓分别为0.8和2.7 kJ/mol,C-C键解离能的平均绝对误差只有3.1 kJ/mol,表明此方法不仅可准确计算正构烃标准生成焓和C-C键解离能,而且还能正确预测C-C键解离能变化趋势。     

乙腈介质中S-NO键异裂能和均裂能的测定

近年来, 大量研究表明, 一氧化氮在许多生命过程(如免疫、神经传导和血管扩张等)中发挥着十分重要的作用[1～4]. 然而, 文献[5]的研究表明, NO在生命体内很少以游离形式存在, 绝大部分都是与生命体内活线性分子结合着, 其中NO与有机硫以S-NO键方式结合形成的NO蕴合物(Nitric oxide-generating agent)被认为是NO在生命体内贮存、 转移和释放最主要的分子源[5]. 因此, 系统研究各种类型硫键NO蕴合物中S-NO键的断裂能, 可以诠释和预测NO在生命体内的转移方向和转移机制. 由于这一原因, S-NO键断裂能的研究是当今许多键能化学家正致力于解决的最热门课题之一. 10多年来, 我们从事的化学键键能研究, 已为这一领域的深入研究奠定了基础. 前文[6～8]根据热力学循环利用滴定量热法成功地测得了多个系列的N-NO键的异裂能和均裂能. 最近, 我们在此工作的基础上, 通过改变热力学循环方式又成功地利用滴定量热法测得了12个S-亚硝基化合物中的S-NO键的异裂能和均裂能, 其中9个为芳香体系, 3个为脂肪体系, 分别模拟生命体系内芳香体系和脂肪体系中的S-NO键. 本文首次报道其实验结果, 并进行一些讨论.     

Substituent Effect on the C–NO2 and N–NO2 Bond Dissociation Energies of Nitroaromatic Molecules

Six density function theory methods (B3LYP, B3P86, MPWB1K1, MPWPW91, PBEPBE, TPSS1KCIS3) were used to calculate bond dissociation enthalpies of nitro compounds, where the B3P86 method was found to give the most accurate predictions. Using the B3P86 method meta‐ and para‐substituted nitroaromatics were systematically studied for the first time. The remote substituent effects, Hammett relationships, and the origin of the substituent effects were discussed on the basis of the calculated results. Both meta‐ and para‐substituted nitromethyl‐benzenes showed significant substituent effects and a fair correlation against substituent constants σ_p⁺ The ground state effects were found to play the major role in determining the overall substituent effects. Meanwhile, nitroamino‐ benzenes showed irregular substituent effects and a poorer Hammett correlation, where both ground and radical state effects contributed to the overall substituent effects.     

Organometallic‐Mediated Radical Polymerization of Vinylidene Fluoride

An unprecedented level of control for the radical polymerization of vinylidene fluoride (VDF), yielding well‐defined PVDF (at least up to 14 500 g mol^?1) with low dispersity (≤1.32), was achieved using organometallic‐mediated radical polymerization (OMRP) with an organocobalt compound as initiator. The high chain‐end fidelity was demonstrated by the synthesis of PVDF‐ and PVAc‐containing di‐and triblock copolymers. DFT calculations rationalize the efficient reactivation of both head and tail chain end dormant species.     

常见三氟甲基源释放三氟甲基自由基能力的理论计算研究

三氟甲基自由基源（·CF₃）是发展自由基三氟甲基化反应的基础.采用密度泛函理论（M06-2X）,系统研究35个常见三氟甲基源释放CF₃自由基的能力（TR^·DA：trifluoromethyl radical donor ability）及可能的途径.计算结果表明,35个三氟甲基源通过化学键均裂释放三氟甲基自由基所需能量跨度为-21.5至95.2 kcal·mol^-1.单电子转移、卤键和硫键给体（halogen/chalcogen-bond donor）可促进CF₃自由基释放.相关研究结果将有助于理解和设计新自由基三氟甲基化试剂和反应.     

聚偏氟乙烯的氯化改性

研究了聚偏氟乙烯 (PVDF)自由基引发的氯化反应。考察了各种因素 ,如氯化剂、引发剂的种类及浓度 ,反应介质、反应温度和反应时间的影响 ,确定了合成氯化PVDF的最佳反应条件。采用碱熔法测定氯含量 ,用HNMR进行了结构表征 ,并用溶度参数法、接触角法、DTA TG等方法对PVDF氯化前后的溶解性、附着力、熔点等性能进行了测试。结果表明 ,氯原子成功地引入到了PVDF上 ,当氯含量增加到 8 3 %时 ,氯化PVDF的熔点由 1 63℃降至 1 3 0℃左右 ,附着力也有了明显的改善 ,与水的接触角由 90°降至 5 4°,由不溶于丙酮变为溶于丙酮 ,对甲醇和四氯化碳的溶度参数的变化也说明了氯化PVDF的溶解性能变好 ,由TG曲线可知 ,氯化PVDF的热稳定性比改性前虽有一定的降低 ,但其分解温度仍在 3 0 0℃以上     

Why Static O-H Bond Parameters Cannot Characterize the Free Radical Scavenging Activity of Phenolic Antioxidants: ab initio Study

Recently, selecting high efficient phenolic antioxidants with low toxicity was paid much attention1-4. Moreover, quantitative structure-activity relationships (QSAR) for phenolic antioxidants have been investigated to accelerate the selection process5-7. Hence, how to theoretically characterize the free radical scavenging activity of phenolic antioxidants is important and significant. Although the parameters characterizing O-H bond dissociation energy or enthalpy (BDE) correlate well with …     

Novel Source of Trifluoromethyl Radical As Efficient Initiator for the Polymerization of Vinylidene Fluoride

A persistent perfluoroalkyl radical (PPFR), perfluoro‐3‐ethyl‐2,4‐dimethyl‐3‐pentyl, is shown to be a good source of •CF₃ radicals and a useful radical capable of initiating the polymerization of vinylidene fluoride (VDF). NMR characterizations of the resulting PVDF homopolymers showed that polymerization of VDF was exclusively initiated by •CF₃ radicals. The addition of •CF₃ radical onto VDF was regioselective leading to CF₃‐CH₂‐CF₂‐PVDF and the CF₃ end‐group acted as an efficient label to assess the molecular weights by ¹⁹F NMR spectroscopy. Various [PPFR]₀/[VDF]₀ initial molar ratios lead to CF₃–PVDF–CF₃ of different molecular weights. When that ratio decreased, both the molecular weights and the thermostability of these PVDFs increased, showing less defects of chaining and higher crystallinity.     

Si-H, P-H 和 S-H 键离解能Alfa取代基效应研究

CBS-Q and G3 methods were used to generate a large number of reliable Si--H, P---H and S--H bond dissociation energies （BDEs） for the first time. It was found that the Si--H BDE displayed dramatically different substituent effects compared with the C--H BDE. On the other hand, the P---H and S--H BDE exhibited patterns of substituent effects similar to those of the N--H and O--H BDE. Further analysis indicated that increasing the positive charge on Si of XSiH3 would strengthen the Si--H bond whereas increasing the positive charge on P and S of XPH2 and XSH would weaken the P---H and S--H bonds. Meanwhile, increasing the positive charge on Si of XSiH2^＋ stabilized the silyl radical whereas increasing the positive charge on P and S in XPH＂ and XS＊ destabilized P- and S-centered radicals. These behaviors could be reasonalized by the fact that Si is less electronegative than H while P and S are not. Finally, it was demonstrated that the spin-delocalization effect was valid for the Si-, P- and S-centered radicals.