1,4-苯并二氮杂-2-酮的电荷转移性质

本文用分光光度法测定了标题化合物分别与TCNE和对甲苯酚钾形成的电荷转移络合物的电子跃迁能hvcr并计算了它们的电子亲合力(E_A)和电离势(I_p),还测定了络合物的热力学常数(K,ΔH,ΔS)。结果表明,该化合物不但可以作为电荷受体,也可以作为电荷给体。处于分子7位取代基的Hammett常数σ与hv_cr(或ΔH)有线性关系。     

取代基效应对N-4-取代苯亚甲基苯胺与N-4-取代苯亚甲基环己胺NMR和UV光谱影响的差异性

合成了N-4-取代苯亚甲基苯胺(1)与N-4-取代苯亚甲基环己胺(2)两个系列化合物, 测定其¹³C和¹H 核磁共振(NMR)化学位移以及紫外(UV)吸收光谱. 定量对比了取代基效应对两个系列化合物CH=N键的¹³CNMR化学位移δ_C(C=N)和¹H NMR化学位移δ_H以及UV吸收光谱最大波长能量(v_max)的影响差异. 研究结果表明,对于分子骨架相似的化合物(1)和(2), 取代基效应的作用方式存在多样性: (i)化合物(1)的δ_C(C=N)、δ_H以及v_max受到基团的特殊交叉相互作用(Δσ²)的影响显著, 而Δσ²对化合物(2)相应性能的影响很小; (ii)无论化合物(1)还是化合物(2), 取代基场/诱导效应σ_F和共轭效应σ_R对δ_C(C=N)的影响为负相关, 而对δ_H的影响为正相关, 它们对δ_C(C=N)和δ_H的影响正好相反. 另一方面, 场/诱导效应σ_F对(1)和(2)的δ_C(C=N)影响重要, 而对它们的δ_H影响很小; (iii)化合物(1)和(2)的δ_C(C=N)、δ_H以及v_max的变化规律, 可分别建立通用方程表达, 其中与CH=N的N原子键连苯基的影响可由指示变量(I)表示, 该苯基对三种性能分别有固定的贡献.     

单金属锰、铁卟啉对空气氧化α-蒎烯的催化作用及取代基效应

以α-蒎烯为底物,空气作氧化剂,研究了苯环上带有不同取代基团的单锰卟啉和单铁卟啉对空气氧化α-蒎烯的催化作用及反应中的取代基效应.结果表明,单锰卟啉及单铁卟啉催化氧化α-蒎烯得到双键和烯丙位一、二级碳氢键的氧化产物,没有烯丙位三级碳氢键的氧化产物.环氧化合物是主要产物,而且氧化产物的产率随时间的变化呈较好的线性关系.随着苯环上meso位取代基Cl,CH3,OCH3和OH的供电子能力的增强,锰卟啉和铁卟啉对α-蒎烯的催化活性逐渐减弱,α-蒎烯的转化率逐渐降低.锰卟啉和铁卟啉的催化反应表观速率常数k与环外苯基上的取代基特性常数σ均呈良好的线性关系,Hammett关系式分别为lnk=1.2168σ-7.9968,lnk=0.6251σ-8.2426;线性相关系数分别为0.9507和0.9715.     

氧化腈与丙炔1,3-偶极环加成反应中区域选择性的理论研究

用密度泛函(DFT)B3LYP/6-311＋＋G**方法研究了氧化腈(RCNO, R＝F, NO₂, OCH₃, OH, COOCH₃, CHO, CONH₂, H, CH₃)与丙炔的1,3-偶极环加成反应, 并且计算了不同温度下的反应速率常数, 讨论了氧化腈上不同取代基R的取代效应和温度对反应区域选择性的影响. 结果显示, 氧化腈与富电子亲偶极体——炔烃反应, 5-取代反应占优势; 氧化腈上取代基R为强吸电子基团时或在较高温度下, 有利于4-取代反应的进行.     

NO2气相硝化金刚烷的计算研究

运用密度泛函理论(DFT)和半经验MO-PM3方法研究了NO₂气相硝化金刚烷反应机理. 计算结果表明, NO₂不能直接取代金刚烷H; 在B3LYP/6-311＋＋G(3df,2pd)//B3LYP/6-31G* 较高水平下, 对三个可能机理的反应势垒(E_a)的精确计算表明, 该反应的决速步骤为NO₂中O和N进攻1-H的竞争过程, 且1-硝基金刚烷为主要产物. NO₂中O进攻1-H决速反应过程中, 分子几何、原子自然电荷及IR光谱变化表明, C—H键的断裂和N—H键的形成是一个协同过程; 参与新键形成和旧键断裂原子C(1), H(11), O(28), O(29)和N(27)的原子自然电荷及与其相关的键长、键角有明显的变化. 反应过程中体系偶极矩的变化表明, 极性溶剂能降低反应势垒, 有利于反应的进行.     

2-(5-取代苯氧甲基-1,3,4-噻二唑-2-亚胺基)-5-(取代苯基亚甲基)-4- 噻唑啉酮的合成

以2-氨基-5-取代苯氧甲基-1,3,4-噻二唑(1)为起始原料, 合成了中间体2-氯乙酰氨基-5-取代苯氧甲基-1,3,4-噻二唑)-2-乙酰亚胺(2)和2-(5-取代苯氧甲基-1,3,4-噻二唑-2-亚胺基)-4-噻唑啉酮(3), 化合物3进一步与取代苯甲醛发生类Knoevenagle缩合反应, 得到了一系列2-(5-取代苯氧甲基-1,3,4-噻二唑-2-亚胺基)-5-(取代苯基亚甲基)-4-噻唑啉酮类化合物4a～4p. 目标化合物4a～4p的结构经IR, ¹H NMR和元素分析确证.     

1,4-二氢-5H-(二硝基亚甲基)-四唑(DNMT)的合成、晶体结构和热行为研究

利用1-氨基-1-肼基-2,2-二硝基乙烯(AHDNE)和亚硝酸钾在酸性水溶液中合成出了高能富氮化合物1,4-二氢- 5H-(二硝基亚甲基)-四唑(DNMT), 并在水溶液中培养出DNMT•2H2O单晶. 该晶体属正交晶系, 空间群为Pnma, 晶胞参数为: a＝10.392(2) Å, b＝15.809(4) Å, c＝5.0640(11) Å, V＝832.0(3) Å3, Dc＝1.629 g•cm－3, μ＝0.163 mm－1, F(000)＝432, Z＝4, R1＝0.0311, wR2＝0.0885. 运用Gaussian 03程序, 在6-311＋＋G**基组水平上, 用HF和B3LYP两种方法对DNMT分子进行了几何全优化和相应的电荷、轨道能量分析. 理论计算和热分析结果表明DNMT呈现较差的热稳定性.     

Meso-2,3-二氰基-2,3-二苯基丁二酸二乙酯熔融相热异构化反应动力学及中间体EPR测定

测定了2,3-二氰基-2,β-二苯基丁二酸二乙酯meso-异构体熔融相的热异构化反应动力学及苯环对位为X(X=OCH₃,CH₃,H,Cl,NO₂)的相应二乙酯反应中间体自由基的EPR谱,自由基的结构由计算机模拟确定.结果表明,在实验温度范围内,平衡常数随温度的升高而降低.热力学数据为:ΔH_dl-meao= - 18.02 kJ/mol, ΔS_dl-meao= - 26.51 J/mol·K, ΔH^≠ = 151.78 kJ/mol, ΔS^≠ = 71.64 J/mol·K.反应机理是内消旋体的中心碳-碳键发生均裂,生成α-氰基-α-乙氧甲酰基-P-X取代苄基自由基,再重新结合时发生异构化,生成dl-异构体.     

四Schiff碱(二苯并-18-冠-6)及其钾(Ⅰ)/钴(Ⅱ)配合物的合成和性质

由二苯并-18-冠-6出发,合成了4′,4″,5′,5"-四(2-羟基苯亚甲基亚氨基)二苯并-18-冠-6(L1H4)及其5位取代衍生物(取代基R=CH3,OH,OCH3,Cl,NO2)L2H4～L6H4.它们依次与硝酸钾和醋酸钴反应,制得1:1:2的钾(Ⅰ)/双钴(Ⅱ)配合物LCo2·2H2O·KNO3(L=L5,L6)或其某些二氧加合物LCo2(2O2)·2H2O·KNO3(L=L1～L4).考察了取代基R和冠醚环配合的钾离子对二氧加合物形成及稳定性的影响.结果表明,含吸电子基(R=Cl,NO2)的钾(Ⅰ)/双钴(Ⅱ)配合物不能形成二氧加合物;冠环中的钾离子会导致二氧加合物中两个Co-O2键热稳定性的差异.     

CH2＝CClF hν >•CH＝CClF＋H光解反应的理论研究

采用UHF, CIS和CASSCF方法, 在aug-cc-pvdz基组水平上对CH₂＝CClF ^hν >•CH＝CClF＋H的光解反应通道及其后续反应作了研究. 计算表明: 分子吸收一个光子后, 在第一电子激发态(S₁)经过一个过渡态解离与Cl原子同侧的C—H键, 这与用CIS方法计算垂直激发得到的π→σ^*_C—H跃迁及其对Frank-Condon点的计算中分子的单占轨道和键电荷密度变化所预测的结果是一致的. 光解产物•CH＝CClF(基态)还可再发生反应, 经过渡态解离C—Cl键或是C—F键.     

Anomeric effect in "high energy" phosphate bonds. Selective destabilization of the scissile bond and modulation of the exothermicity of hydrolysis

A natural bonding orbital (NBO) analysis of phosphate bonding and connection to experimental phosphotransfer potential is presented. Density functional calculations with the 6-311++G(d,p) basis set carried out on 10 model phosphoryl compounds verify that the wide variability of experimental standard free energies of hydrolysis (a phosphotransfer potential benchmark) is correlated with the instability of the scissile O-P bond through computed bond lengths. NBO analysis is used to analyze all delocalization interactions contributing to O-P bond weakening. Phosphoryl bond lengths are found to correlate strongest (R = 0.90) with the magnitude of the ground-state n(O) --> sigma*(O-P) anomeric effect. Electron-withdrawing interactions of the substituent upon the sigma(O-P) bonding orbital also correlate strongly with O-P bond lengths (R = 0.88). However, an analysis of sigma*(O-P) and sigma(O-P) populations show that the increase in sigma*(O-P) density is up to 6.5 times greater than the decrease in sigma(O-P) density. Consequently, the anomeric effect is more important than other delocalization interactions in impacting O-P bond lengths. Factors reducing anomeric power by diminishing either lone pair donor ability (solvent) or antibonding acceptor ability (substituent) are shown to result in shorter O-P bond lengths. The trends shown in this work suggest that the generalized anomeric effect provides a simple explanation for relating the sensitivity of the O-P bond to diverse environmental and substituent factors. The anomeric n(O) --> sigma*(O-P) interaction is also shown to correlate strongly with experimentally determined standard free energies of hydrolysis (R = -0.93). A causal mechanism cannot be inferred from correlation. Equally, a P-value of 1.2 x 10(-4) from an F-test indicates that it is unlikely that the ground-state anomeric effect and standard free energies of hydrolysis are coincidentally related. It is found that as the exothermicity of hydrolysis increases, the energy stabilization of the ground-state anomeric effect increases with selective destabilization of the high-energy O-P bond to be broken in hydrolysis. The anomeric effect therefore partially counteracts a larger resonance stabilization of products that makes hydrolysis exothermic and needs to be considered in achieving improved agreement between calculated and empirical energies of hydrolysis. The avenues relating the thermodynamic behavior of phosphates to underlying structural factors via the anomeric effect are discussed.     

Comparison of the electronic structures of imine and hydrazone side-chain functionalities with the aid of 13C and 15N NMR chemical shifts and PM3 calculations. The influence of C=N-substitution on the sensitivity to aromatic substitution

Benzaldehyde derivatives possessing a C=N double bond in the side-chain of the aromatic ring exhibit a reverse dependence of the (13)C NMR chemical shifts of the C=N carbon on the benzylidenic substituents X. Thus, electron-withdrawing substituents cause shielding (shift is reduced), while electron-donating ones cause deshielding. The origin of this phenomenon, which is in contrast with the idea of the generalized electronic effect, is extensively studied here by comparing the behavior of sets of benzaldehyde derivatives bearing various substitutents Y on the C=N nitrogen (Y-N=CH-C(6)H(4)-X). The effects of substituents X on the C=N unit change when Y is varied. Combination of the influences of the substituents X and Y gives a sensitive balance between the different resonance structures of the compounds. Our graphical treatment, where the rho(I) and rho(R) values observed for substituent X are plotted against the sigma(p)(+) value of substituent Y, is a novel use of Hammett-type substituent parameters. The justification of this method and our conclusions could be verified, for instance, by the fair correlation between the rho(I) or rho(R) values and the atomic charges of the imine carbon of the unsubstitued phenyl derivatives as well as by the correlations of the relevant bond orders and/or bond lengths both with the substituent parameters and with the atomic charges.     

纳米结晶体Ni0.5Zn0.5Fe2O4对高氯酸铵热行为及分解反应动力学的影响

采用差示扫描量热法(DSC)、热重和微分热重(TG-DTG)及固相原位反应池/快速扫描傅立叶变换红外联用技术(hyphenated in situ thermolysis/RSFTIR)研究了纳米结晶体Ni_0.5Zn_0.5Fe₂O₄与高氯酸铵(AP)组成的混合物的热行为和分解反应动力学。结果表明：Ni_0.5Zn_0.5Fe₂O₄使得AP的低、高温分解放热峰温分别提前17.44 K和27.74 K,并使得对应的分解热分别增加3.7 J·g^-1和193.7 J·g^-1。Ni_0.5Zn_0.5Fe₂O₄并不影响AP的晶转温度和晶转热。Ni_0.5Zn_0.5Fe₂O₄使得AP的TG曲线出现3个阶段,并使得后2个失重阶段的初始和终止温度都有所提前。凝聚相分解产物分析表明Ni_0.5Zn_0.5Fe₂O₄加速了凝聚相AP的分解及氨气的释放。含Ni_0.5Zn_0.5Fe₂O₄的AP的高温分解反应的动力学参数E_a=238.88 kJ·mol^-1,A=1018.59 s^-1,动力学方程可表示为dα/dt=10^18.99(1-α)[-ln(1-α)]^3/5e^-2.87×104T。始点温度(T_e)和峰顶温度(T_p)计算得出AP的热爆炸临界温度值分别为:574.83 K和595.41 K。分解反应的活化熵(ΔS^≠)、活化焓(ΔH^≠)和活化能(ΔG^≠)分别为:109.61 J·mol^-1·K^-1、236.49 kJ·mol^-1及172.58 kJ·mol^-1。     

Theoretical study of the decomposition reactions in substituted nitrobenzenes

The influence of substituent nature and position on the unimolecular decomposition of nitroaromatic compounds was investigated using the density functional theory at a PBE0/6-31+G(d,p) level. As the starting point, the two main reaction paths for the decomposition of nitrobenzene were analyzed: the direct carbon nitrogen dissociation (C6H5 + NO2) and a two step mechanism leading to the formation of phenoxyl and nitro radicals (C6H5O + NO). The dissociation energy of the former reaction was calculated to be 7.5 kcal/mol lower than the activation energy of the second reaction. Then the Gibbs free energies were computed for 15 nitrobenzene derivatives characterized by different substituents (nitro, methyl, amino, carboxylic acid, and hydroxyl) in the ortho, meta, and para positions. In meta position, no significant changes appeared in the reaction energy profiles whereas ortho and para substitutions led to significant deviations in energies on the decomposition mechanisms due to the resonance effect of the nitro group without changing the competition between these mechanisms. In the case of para and meta substitutions, the carbon-nitro bond dissociation energy has been directly related to the Hammett constant as an indicator of the electron donor-acceptor effect of substituents.     

Theoretical and Structural Analysis of Long CC Bonds in the Adducts of Polycyanoethylene and Anthracene Derivatives and Their Connection to the Reversibility of Diels–Alder Reactions

X‐ray structure determinations on four Diels–Alder adducts derived from the reactions of cyano‐ and ester‐substituted alkenes with anthracene and 9,10‐dimethylanthracene have shown the bonds formed in the adduction to be particularly long. Their lengths range from 1.58 to 1.62 Å, some of the longest known for Diels–Alder adducts. Formation of the four adducts is detectably reversible at ambient temperature and is associated with free energies of reaction ranging from ?2.5 to ?40.6 kJ mol^?1. The solution equilibria have been experimentally characterised by NMR spectroscopy. Density‐functional‐theory calculations at the MPW1K/6‐31+G(d,p) level with PCM solvation agree with experiment with average errors of 6 kJ mol^?1 in free energies of reaction and structural agreement in adduct bond lengths of 0.013 Å. To understand more fully the cause of the reversibility and its relationship to the long adduct bond lengths, natural‐bond‐orbital (NBO) analysis was applied to quantify donor–acceptor interactions within the molecules. Both electron donation into the σ*‐anti‐bonding orbital of the adduct bond and electron withdrawal from the σ‐bonding orbital are found to be responsible for this bond elongation.     

Conformational preference and cis-trans isomerization of 4(R)-substituted proline residues

We report here the conformational preference and prolyl cis-trans isomerization of 4(R)-substituted proline dipeptides, N-acetyl-N'-methylamides of 4(R)-hydroxy-L-proline and 4(R)-fluoro-L-proline (Ac-Hyp-NHMe and Ac-Flp-NHMe, respectively), studied at the HF/6-31+G(d), B3LYP/6-31+G(d), and B3LYP/6-311++G(d,p) levels of theory. The 4(R)-substitution by electron-withdrawing groups did not result in significant changes in backbone torsion angles as well as endocyclic torsion angles of the prolyl ring. However, the small changes in backbone torsion angles phi and psi and the decrease of bond lengths r(Cbeta-Cgamma) or r(Cgamma-Cdelta) appear to induce the increase of the relative stability of the trans up-puckered conformation and to alter the relative stabilities of transition states for prolyl cis-trans isomerization. Solvation free energies of local minima and transition states in chloroform and water were calculated using the conductor-like polarizable continuum model at the HF/6-31+G(d) level of theory. The population of trans up-puckered conformations increases in the order Ac-Pro-NHMe < Ac-Hyp-NHMe < Ac-Flp-NHMe in chloroform and water. The increase in population for trans up-puckered conformations in solution is attributed to the increase in population for the polyproline-II-like conformations with up puckering. The barriers DeltaGct++ to prolyl cis-to-trans isomerization for Ac-Hyp-NHMe and Ac-Flp-NHMe increase as the solvent polarity increases, as seen for Ac-Pro-NHMe. In particular, it was identified that the cis-trans isomerization proceeds through the clockwise rotation about the prolyl peptide bond for Ac-Hyp-NHMe and Ac-Flp-NHMe in chloroform and water, as seen for Ac-Pro-NHMe.     

细菌生长的热动力学性质的研究

前文报导了大肠杆菌在不同培养基中生长的速率及热力学函数.本文在此基础上又测定了不同细菌在相同培养基中生长的规律.细菌生长是一系列非常复杂的过程,为便于研究,使复杂问题简单化,我们采取与过渡状态理论类似的模式进行处理,得出了一些热动力学函数,这些数据为进一步探讨这一复杂过程提供了有用的信息.     

1-乙胺基-3-甲基咪唑四氟硼酸盐吸收CO_2的理论研究

采用密度泛函理论(DFT)对离子液体1-乙胺基-3-甲基咪唑四氟硼酸盐([NH2e-mim][BF4])吸收CO_2的反应机理进行了研究.在B3LYP/6-311++G(d,p)计算水平下,对离子液体[NH2e-mim][BF4]的结构及与CO_2反应的中间体、过渡态和产物进行了全优化,获得了优化结构的构型参数、振动频率和热力学数据.利用自然键轨道(NBO)分析了离子液体[NH2e-mim][BF4]和CO_2的自然电荷布居.计算结果表明,通过阳离子[NH2e-mim]+自偶解离产生的阳离子[NH3e-mim]2+能与阴离子[BF4]-结合形成更强的离子键.根据反应吉布斯自由能变(ΔG0—)和焓变(ΔH0—)的计算结果,判断离子液体[NH2e-mim][BF4]吸收CO_2按理论摩尔比2∶1分步进行反应,吸收过程中质子的转移需克服52.51 k J/mol的能垒.     

Theoretical study on the electrochemical behavior of norepinephrine at Nafion multi-walled carbon nanotubes modified pyrolytic graphite electrode

DFT-B3LYP/6-31G (d, p) and HF/6-31G (d, p) calculations are performed for deoxidized norepinephrineat (NP(R)) and its oxidized form (NP(O)). The electrochemistry of norepinephrineat (NP) was studied by cyclic voltammetry (CV) at a pyrolytic graphite electrode modified by Nafion multi-walled carbon nanotubes (MWNTs) in phosphate buffers at pH 6.0, showing that the standard electrode potential of half reaction for NP(O), H+/NP(R) is 0.75l V. This experimental standard electrode potential of half reaction is consistent with that calculated using the energies of solvation and sum of electronic and thermal free energies of NP(R) and NP(O). The frontier orbital theory and Mülliken charges of molecular explain the electrochemical behavior of CV at modified electrode well. The singlet vertical excited states for NP(R) and NP(O) are also discussed.     

Characterization of pentacarbonyl(4-methylpyridine)chromium(0) complex using density functional theory (DFT) and Hartree-Fock (HF) computational methods

The optimized molecular structure, atomic charges, vibrational frequencies, thermodynamic properties, nuclear magnetic resonance (NMR) and ultraviolet-visible (UV-Vis) spectral data of pentacarbonyl(4-methylpyridine)chromium(0) complex have been investigated by performing ab initio Hartree-Fock (HF) and density functional theory, B3LYP, B3PW91 and BE1PBE methods with 6-311G, 6-311+G(3d,3p) and 6-31G(d,p) basis set. The calculated NMR data at 6-311G basis set, vibrational frequencies at 6-311+G(3d,3p) basis set and the optimized geometric bond lengths and bond angles at 6-31G(d,p) basis set are in good agreement with the corresponding experimental values. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have been simulated. In addition, the transition state and energy band gap and infrared intensities have also been reported.