五嗪含氮取代基衍生物结构和性质的理论研究

采用密度泛函理论(DFT)方法在B3LYP/aug-cc-pvDZ理论水平上研究了CN, NO₂, NH₂, N₃, N₂H, NHNH₂, N₄H和N₄H₃等含氮取代基取代五嗪环上的氢原子生成的衍生物, 预测了它们的分子构型、分解能及含能性质. 对衍生物分解能的研究结果表明, CN和NH₂取代的衍生物的分解能比未取代时更高, 而其余基团的取代使分解能降低; 取代基化合物的生成热越大, 取代五嗪中的氢原子后生成衍生物的生成热也越大. N₄H₃, NO₂, H, N₂H, N₄H, N₃和CN取代的五嗪衍生物的单位原子生成热为72.6～108.9 kJ, 比文献报道的三叠氮基-均三嗪的(70.2 kJ)更高. 对于CN, N₂H, N₄H₃, N₃和N₄H取代的衍生物, 其生成热为871.4～1159.3 kJ•mol^－1, 但N₄H和N₄H₃的分解能较小, 稳定性较差. 因此, N₃, N₂H和CN取代的衍生物可能成为高能量、低感度的含能材料.     

3-硝基-1,2,4-三唑-5-酮(NTO)热分解机理的对称破缺密度泛函理论研究

共价键均裂在含能分子的热分解过程中普遍存在,因此极为重要.然而,以往的理论研究通常用键能(ΔH,BDE)估算均裂能垒,因忽略了熵效应,必然造成较大误差.采用对称破缺密度泛函方法(BS-UB3LYP/6-311+G**),对含能分子3-硝基-1,2,4-三唑-5-酮(NTO)的热分解机理进行了系统研究和梳理,计算了共价键均裂的过渡态及能垒.结果表明,C—NO₂键均裂和随后的自由基复合是最优途径,能垒为216.9 k J?mol^-1 (523 K).随后产生的NO自由基通过多次“复合-均裂”过程促进三唑中间体开环,分解为HNCO,N₂O和CO等小分子,它们相互反应又生成NO₂,N₂和CO₂.这些分解产物与诸多实验观测结果一致.     

3-氨基-4-硝基氧化呋咱含能化合物的设计合成研究

在氧化呋咱环上引入氨基或硝基等功能基团,可提高含能化合物的能量密度和爆炸性能。为了获得更高能量密度的新型含能化合物,本文利用密度泛函理论（DFT）和单、双激发的耦合簇（CCSD）方法探索了以3-酰基叠氮基-4硝基氧化呋咱为起始材料,在二氧六环和水混合溶剂中合成3-氨基-4硝基氧化呋咱的反应机理,给出了反应的势能曲线。结果表明,该反应主要分为两个阶段：3-酰基叠氮基-4硝基氧化呋咱脱N₂后进行Curtious重排产生异氰酸酯;异氰酸酯经水解、羟基扭转、CO₂的脱离形成产物。反应的决速步为CO₂的脱离,能垒为44kcal/mol。因此,加热是实现该合成反应的必要条件。水既绿色环保,又参与反应,是该反应的最佳溶剂。这些结果为3-氨基-4-硝基氧化呋咱的实验合成提供了必要的理论依据。     

基于线性叠氮四核单元的系列二维化合物: 合成, 晶体结构及磁性

分子磁体的设计与合成一直是当今物理和化学的热门研究课题. 受分子磁体启发, 通过引入叠氮磁耦合基团以及长链棒状配体4,4'-二咪唑联苯(L), 我们构筑了三个磁性化合物[Co₂(N₃)₄(L)_2.5]_∞(1), [Ni₂(N₃)₃(NO₃)(L)_2.5]_∞(2)和[Mn₂(N₃)₄(L)_2.5]_∞(3). 结构分析显示, 这是三个同构化合物, 展现了一种基于线性叠氮四核单元的二维层网络. 有意义的是, 这种线性叠氮四核单元还未曾被人报道. 磁性研究表明, 三个化合物都是铁磁耦合, 这是由于EO-叠氮所导致的. 通过拟合实验数据, 我们得到了三个化合物的磁耦合常数, 进一步验证了上面磁构相关性的讨论.     

化学反应的内禀反应坐标法(Ⅷ)——甲基叠氮热解反应的反应路径解析

采用内禀反应坐标法完成了对甲基叠氮热解反应途径的微观动力学解析.结果表明甲基叠氮的热解是以伴随N₂消除后发生1,2-H迁移的协同方式完成的,属协同的非同步反应,此机制可解释(H₃C)nH_3-nC-N₃(n=0～2)烷基叠氮系列热解温度的光电子能谱结果.     

CL-20热分解反应机理的ReaxFF分子动力学模拟

为探究固相CL-20热分解反应机理,本文采用反应分子动力学ReaxFF MD模拟研究了含有128个CL-20分子的超胞模型在800–3000 K温度下的热分解过程。借助作者所在课题组研发的反应分析及可视化工具VARxMD得到了热分解过程中多种反应中间物和较为全面的反应路径。氮氧化物是CL-20初始分解的主要中间产物,其中NO₂是数量最多的初始分解产物,观察到的中间物NO₃的生成量仅次于NO₂。统计CL-20初始分解的所有反应后发现,在所有考察温度下CL-20初始分解路径主要是N―NO₂断裂反应和C―N键断裂引起开环的单分子反应路径。N―NO₂断裂反应数量在高温下显著增多,而C―N键断裂引起的开环反应数量随温度升高变化不大。在低温热分解模拟中还观察到CL-20初始分解阶段生成的NO₂会发生双分子反应—从CL-20分子中夺氧生成NO₃。对CL-20热分解过程中环结构演化进行分析后发现,CL-20分解的早期反应中间物主要为具有3元或2元稠环结构的吡嗪衍生物,随后它们会分解形成单环吡嗪。吡嗪六元环结构在热分解过程中非常稳定,这一模拟结果支持Py-GC/MS实验中提出吡嗪存在的结论。CL-20中的咪唑五元环结构相对不稳定,在热分解过程中会发生开环分解而较早消失。由ReaxFF MD模拟得到的3000 K高温热分解产物N₂,H₂O,CO₂和H₂的数量与爆轰实验的测量结果定量吻合。本文获得的对CL-20热分解机理的认识表明ReaxFF MD结合VARxMD有可能为深入了解热刺激下含能材料复杂化学过程提供一种有前景的方法。     

中心为氨基、末端为硝基的苯乙炔树枝状分子的合成

将固定相合成与“收敛/发散”方法相结合,合成了第一、二代苯乙炔树枝状分子.通过Heck-Cassar-Sonogashira-Hagihara偶联反应,将其中心和末端分别修饰上供电子的氨基和拉电子的硝基,得到第一、二代中心为氨基、末端为硝基的苯乙炔树枝状分子NH₂-G1-(NO₂)₂和NH₂-G2-(NO₂)₄.用傅里叶变换红外光谱跟踪了整个固定相合成过程.苯乙炔树枝状分子的紫外-可见吸收光谱呈现出规律性变化.     

苯并氧化呋咱稳定性和异构化的DFT和ab initio研究

运用B3LYP/6-31G(d)密度泛函理论（DFT）方法对苯并氧化呋咱、邻二亚硝基苯及其间的异构化反应进行了计算研究。结果表明,苯并氧化呋咱的分子总能量比邻二亚硝基苯的低;由苯并氧化呋咱异构为邻二亚硝基苯的正向反应活化能（Ea+=51.0kJ/mol）,与文献实测值（58.6kJ/mol）较接近,而其逆向反应活化能（Ea-=4.6kJ/mol）很小,从而揭示了苯并氧化呋咱比邻二亚硝基苯更稳定·此外,进行了HF/3-21G、HF/6-31G(d)和MP2/6-31G(d)//6-31G(d)水平下相应的计算,发现B3LYP-DFT的结果较abinitio为优。谐振动频率的B3LYP/6-31G(d)计算还支持了邻二亚硝基苯为苯并氧化呋咱“自-自”互变重排反应的中间体。     

对流层大气NO3与N2O5的实地测量

大气硝基(NO₃)自由基和五氧化二氮(N₂O₅)是对流层大气化学反应的核心物种,对于理解大气氧化性、二次有机气溶胶生成、活性卤素化学和全球硫素循环等对流层大气化学研究的关键问题具有重要意义。大气NO₃自由基和N₂O反应活性高、大气寿命短、浓度低,其定量分析非常具有挑战性。本文总结了大气NO₃自由基与N₂O₅的实地测量方法,并对差分光学吸收光谱(DOAS)、腔衰荡光谱(CRDS)、腔增强光谱(CEAS)、激光诱导荧光光谱(LIF)、电子顺磁共振谱(MIESR)和化学离子化质谱(CIMS)等六类技术方法的准确度、精确度、时间分辨率、测量干扰、标定方法和系统稳定性等方面进行了系统比较。综合分析认为吸收光谱法是对流层NO₃自由基与N₂O₅测量技术的发展方向,其中近期发展起来的腔技术(CRDS和CEAS)显示出较好的应用潜力。但是我国实际大气环境中普遍存在高浓度的颗粒物污染,如何在高颗粒物条件下实现NO₃自由基与N₂O₅的精密准确测量具有挑战性。本文进一步归纳了NO₃自由基与N₂O₅在城市、森林、自由大气和海洋海岸等典型大气环境条件下的浓度水平和主要科学发现,探讨了一些亟待解决的问题和可能的重点研究方向。     

N2O在焦炭表面异相生成和分解机理的密度泛函理论研究

选用合理简化的焦炭模型,对煤焦燃烧过程中N₂O的异相生成和分解机理进行了分子水平上的研究。采用UB3LYP/6-31G(d)密度泛函理论方法优化得到了反应路径上反应物、产物、中间体和过渡态的几何构型和各中间反应的活化能和反应焓变。NO与其预先吸附在焦炭表面解离生成的表面氮组分反应生成N₂O的路径有两个,需要克服的势垒分别为69.3kJ/mol和200.0kJ/mol;NO亦可直接与焦炭中的吡啶氮结合释放出N₂O,该反应路径所需克服的最大势垒为418.0kJ/mol。N₂O可在焦炭表面分解释放出N₂,异相分解反应为一步反应,计算所得活化能为100.8kJ/mol。N₂O的异相生成和异相分解反应均为放热反应。采用经典过渡态理论计算得到了各路径中速率控制步骤的反应速率常数。低温条件下,N₂O的异相分解反应速率略低于其异相生成速率,随着温度的升高,两者逐渐接近,说明高温条件有利于N₂O的异相分解。     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.