全氟烷基磺酸酯C—O键断裂的同面SN2反应

用密度泛函理论研究了CF₃SO₃CF₂CF₃＋F^－的碳氧键断裂反应的机理. 首先, 用DFT方法优化了反应物、中间体、过渡态、产物的平衡构型, 分析了碳氧键断裂反应的势能面变化. 发现在S_N2反应机理中, 除了S—O断裂S_N2反应外, 引起C—O键断裂的同面进攻也是一个可能的反应途径. 理论计算表明, 最终反应的产物是受热力学控制的, S—O键的断裂绝对地优于C—O的断裂. 因此, C—O断裂的同面机理虽然是可能的, 但却难以被实验观察到. 本文还讨论了端基 —F₃在同面S_N2反应中的邻位效应, 以及基组对这个效应的影响.     

HNCO ¾®HN+CO势能面研究

用从头算方法, 在UHF/6-311G**和CIS/6-311G**水平上,分别考察了异氰酸光解反应HNCO ¾®HN+CO在基态(S₀)、第一激发三态(T₁)和第一激发单态(S₁)势能面上的解离曲线.并找到了S₁/T₁, T₁/S₀, S₁/S₀势能面的交叉点, 给出了极小能量交叉点的特征,在此基础上根据梯度最速下降原理确定了态-态跃迁后交叉点构型在低能态势能面的变化及归宿.计算结果表明光解反应HNCO ¾®HN+CO存在三条竞争反应途径,从动力学观点看,途径A对反应最为有利.     

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.     

非血红素铁超氧化物活化丙烯分子多态反应机理的理论研究

采用密度泛函DFT-B3LYP理论对非血红素铁超氧化物活化丙烯分子多态反应机理进行了探讨. 研究结果表明氢原子抽取过程遵守单态反应机制,主要在基态高自旋七重态势能面进行,且具有较低活化能（ΔG^≠=65.6 kJ·mol^-1）,非血红素铁超氧化物可以作为有效氧化剂抽取氢原子。单态反应机制可能归因于近来建议的交换-加强反应原则（EER,铁中心具有较大交换稳定作用）。对于O-O键的活化,在CASSCF（10,8）/6-31+G（d）//TZVP水平下,势能面交叉区内,高自旋七重态（S₁）和五重态（Q₀）的自旋-轨道耦合（SOC）常数分别为2.26和2.19 cm^-1。轨道分析表明两条发生翻转自旋轨道具有相同空间组成（π_sub^*）,SOC禁阻,因此通过SOC作用反应体系不可能有效地从七重态（S=3）势能面系间穿越到五重态（S=2）势能面,系间穿越可能发生在反应最后的退出阶段。     

非血红素铁超氧化物活化丙烯分子多态反应机理的理论研究

采用密度泛函DFT-B3LYP理论对非血红素铁超氧化物活化丙烯分子多态反应机理进行了探讨.研究结果表明氢原子抽取过程遵守单态反应机制,主要在基态高自旋七重态势能面进行,且具有较低活化能（ΔG^≠=65.6 kJ·mol^-1）,非血红素铁超氧化物可以作为有效氧化剂抽取氢原子。单态反应机制可能归因于近来建议的交换-加强反应原则（EER,铁中心具有较大交换稳定作用）。对于O-O键的活化,在CASSCF（10,8）/6-31+G（d）//TZVP水平下,势能面交叉区内,高自旋七重态（S₁）和五重态（Q₀）的自旋-轨道耦合（SOC）常数分别为2.26和2.19 cm^-1。轨道分析表明两条发生翻转自旋轨道具有相同空间组成（π_sub^*）,SOC禁阻,因此通过SOC作用反应体系不可能有效地从七重态（S=3）势能面系间穿越到五重态（S=2）势能面,系间穿越可能发生在反应最后的退出阶段。     

气相中CrO2+和H2反应的理论研究

用密度泛函UB3LYP/6-311++G(3df, 3pdpd)//6-311G(2dd, p)方法计算研究了在二重态和四重态两个势能面上的气相反应：CrO₂⁺ + H₂→CrO⁺+ H₂O. 对影响反应机理和反应速率的势能面交叉进行了讨论, 并运用Hammond 假设和Yoshizawa 等的内禀反应坐标(IRC)单点垂直激发计算的方法找出了势能面交叉点(crossing point (CP)). 运用碎片分子轨道(fragment molecular orbital(FMO))理论, 对初始复合物2IM1和4IM1的轨道相关进行了分析, 解释了CrO₂⁺活化H—H σ键及H₂迁移的机理.     

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.     

以镁铝水滑石为前驱体制备复合氧化物催化丙酮气相缩合反应

采用共沉淀-恒温晶化法制备了系列镁铝水滑石(Mg-Al-LDH)样品,对镁铝水滑石在500 ℃焙烧得到镁铝复合氧化物(Mg-Al-LDO),采用IR、XRD、CO₂-TPD、SEM及N₂吸附-脱附等方法对Mg-Al-LDH和Mg-Al-LDO进行了表征。在温度250 ℃、液时空速1 h^-1条件下,采用固定床对镁铝复合氧化物催化剂对丙酮缩合反应的性能进行微反活性评价。研究结果表明,晶化时间与镁铝复合氧化物的弱碱性位和强碱性位的密度相关。丙酮缩聚反应的主要产物为异佛尔酮(IP)和异丙叉丙酮(MO),以及少量的异丙烯基丙酮、双丙酮醇,均三甲苯等。丙酮缩聚制备异佛尔酮的反应需要催化剂表面弱碱性位(S_w)与强碱性位(S_s)的协同作用,S_w与S_s需要匹配。晶化12 h得到的镁铝复合氧化物催化剂(LDO-12)的S_w/S_s=1.3,异佛尔酮(IP)选择性为65.3%,单程有效收率(IP+MO)为14.8%。     

叠氮化氰的光解离机理

采用多参考态方法,在MRCI+Q//CAS(10,9)/6-311+G(2df)水平上对叠氮化氰(N3CN)的光解离机理进行理论研究.优化得到基态(S0)和低激发态(S1、S2、T1)势能面上的极小点、过渡态、内转换交叉点(IC-S1/S0)和隙间窜跃交叉点(ISC-S1/T1)的结构和能量,构建反应势能面.在MRCI+Q//CAS(10,9)水平上计算N3CN的垂直激发能,并和实验值进行对比.结果表明,在S0、S1、S2和T1态势能面上,N—N键断裂生成N2+NCN是主要解离途径,而C—N键断裂通道是次要通道.实验观测到220 nm处的吸收峰对应分子由S0态到S1态的激发,对应主要光解离产物为NCN[a1△g];而在275 nm处的吸收峰则对应分子被激发到T1态,然后直接生成基态产物NCN[X3Σg-].我们的理论结果与实验测量符合得很好.     

CH2CO＋CH2的多通道反应的理论研究

利用密度泛函(DFT)和自然键轨道理论(NBO)及高级电子耦合簇[CCSD(T)]和电子密度拓扑(AIM)方法, 对单重态和三重态CH₂与CH₂CO反应的微观机理进行了研究. 在B3LYP/6-311＋G(d,p)水平上优化了反应通道各驻点的几何构型. 在CCSD(T)/6-311＋G(d,p)水平上计算了各物种的单点能量, 并对总能量进行了校正. 计算表明, 单重态CH₂与CH₂CO的C—H键可发生插入反应, 与C＝C、C＝O可发生加成反应, 存在三条反应通道, 产物为CO和C₂H₄, 从能量变化和反应速控步骤能垒两方面考虑, 反应II更容易发生. 对反应通道中的关键点进行了自然键轨道及电子密度拓扑分析. 三重态CH₂与CH₂CO的反应存在三条反应通道, 一条是与C-H键的插入反应, 另一条是三重态CH₂与C＝C发生加成反应, 产物为CO和三重态C₂H₄, 通道II势垒较低, 更容易发生. 最后一条涉及双自由基的反应活化能最大, 最难发生.     

A Theoretical Investigation of the Decomposition Reactions of Ethyl Formate in the S1 and T1 States

This study investigates the decomposition reactions of ethyl formate in the S₁ and T₁ states. The dissociation channels leading to HCOOH + C₂H₄, CH₃CH₂O + HCO, CH₃CH₂OCO + H, and CH₃CH₂ + HCO₂ were studied. The major reactions of ethyl formate in the S₁ and T₁ states are isomerization to the biradical CH₂CH₂OC(OH)H and dissociation to CH₃CH₂O + HCO. All the stationary and intersection points were optimized at the CAS(10,8) level of theory with the 6‐31G(d,p) and 6‐311G(2df,2pd) basis sets. Single‐point CASPT3 energy was calculated for each of the stationary and intersection points. Microcanonical rate constants were also calculated for each of the reactions by using the RRKM theory.     

Photodissociation of acryloyl chloride in the gas phase

The 193 nm photodissociation dynamics of CH2 CHCOCl in the gas phase has been examined with the technique of time-resolved Fourier transform infrared emission (TR-FTIR) spectroscopy.Vibrationally excited photofragments of CO (≤ 5),HCl (≤ 6),and C2H2 were observed and two photodissociation channels,the C-Cl fission channel and the HCl elimination channel have been identified.The vibrational and rotational state distributions of the photofragments CO and HCl have been acquired by analyzing their fully rotationally resolved v→v-1 rovibrational progressions in the emission spectra,from which it has been firmly established that the mechanism involves production of HCl via the four-center molecular elimination of CH2 CHCOCl after its internal conversion from the S1 state to the S0 state.In addition to the dominant C-Cl bond fission along the excited S1 state,the S1→S0 internal conversion has also been found to play an important role in the gas phase photolysis of CH2 CHCOCl as manifested by the considerable yield of HCl.     

A Theoretical Investigation of the Decomposition Reactions of Ethyl Formate in the S0 State

This study revisits the stability of the possible conformations and the decomposition reactions of ethyl formate in the S₀ state using the (U)MP2, MP4SDTQ, CCSD(T), and (U)B3LYP methods with various basis sets. The transition states of the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, CH₂O + CH₃CHO, HCOH + CH₃CHO, C₂H₆ + CO₂, and H₂ + CH₂CHOCHO are determined. The microcanonical rate constants derived from the RRKM theory are calculated for each of the decomposition reactions. The high‐pressure limit rate constants are calculated for the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, and CH₂O + CH₃CHO.     

硫杂杯[4]芳烃氧化膦衍生物的合成与晶体结构

合成了部分取代的硫杂杯[4]芳烃氧化膦衍生物, 二(亚甲基二苯基氧化膦)对叔丁基硫杂杯[4]芳烃(化合物1), 培养了化合物的单晶, 用Smart 1000 CCD衍射仪测定了其晶体结构. 结果表明, 1的组成为: C₆₆H₇₀O₆P₂S₄•2CH₃OH, 属三斜晶系, P1空间群, 晶胞参数a＝1.3453(6) nm, b＝1.5289(7) nm, c＝1.7893(9) nm; α＝75.707(9)°, β＝69.131(8)°, γ＝79.734(9)°, Z＝2; V＝3.316(3) nm³, d＝1.215 g/cm³, F(000)＝1288, μ (Mo Kα)＝0.244 mm^－1, R₁＝0.0625, wR₂＝0.1372. 杯芳烃分子采取了锥式构象.     

Mechanistic Photodissociation of Glycolaldehyde: Insights from Ab Initio and RRKM Calculations

Herein we report a theoretical study on mechanistic photodissociation of glycolaldehyde, HOCH₂CHO. Equilibrium structures, transition states, and intersection structures for the α‐C? C and ‐C? H bond fissions and the β‐C? O bond fission in the excited states are determined by the complete active space self‐consistent field (CASSCF) method. Based on the CASSCF optimized structures, the potential energy profiles for the dissociations are refined by performing single‐point calculations using the multi‐state multi‐reference CASSCF second order perturbation (MS‐MR‐CASPT2) method. With a low excitation energy of 280–340 nm, the T₁ α‐C? C and β‐C? O bond fissions following intersystem crossing from the S₁ state are the predominant and comparable channels, whereas the α‐C? H bond fissions both in the S₁ and in the T₁ states are nearly prohibited due to the relevant high barriers. The rate constants for the T₁ α‐C? C and β‐C? O bond fissions are also calculated by RRKM theory. Furthermore, the S₀ reactions can occur as a consequence of intersystem crossing via T₁/S₀ intersection points resulting from the T₁ C? C and C? O bond cleavages. This photodissociation mechanism is consistent with recent experimental studies.     

Understanding of Photo-Induced Reversible Rearrangement from Borepin to Borirane

The first reversible photoisomerization between a borepin and a borirane was reported in the photo-induced reactions of B(npy)Ar₂ (npy=2-(naphthalen-1-yl) pyridine, Ar=phenyl or electron rich aryl; S. Wang, et al. Angew. Chem. Int. Ed. 2019 , 58, 6683–6687). In this work, the detailed mechanisms of the unprecedented reversible photoisomerization between the borepin (compound a ) and the borirane (compound b ) of B(npy)Ph₂ in the first excited singlet (S₁) state and the ground (S₀) state were studied by carrying out calculations with the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT). The calculation results show that photoexcitation of a -S₀ at 365 nm and b -S₀ at 450 nm populate their S₁ state with evident charge transfer characteristics. The photoisomerization is triggered in the S₁ state and ends in the S₀ state, at which the intersection points in a (S₁/S₀)_x intersection seam participate in and promote phenyl migration and ring-closure processes. Furthermore, we reveal that the not large energy difference (less than 0.6 eV) and similar conjugation properties of π electrons between a -S₀ and b -S₀ are responsible for their unique photo-reversible reactivity, compared with those of the isomers of the thermally reversible compound B(ppy)Mes₂. Our results contribute to an understanding of the excited-state reactivity of organoboron compounds and will be useful to support the design of new boron-based photo-responsive materials.     

刺乌头碱氢溴酸盐的合成及晶体结构

报道了以双溴代烷烃和刺乌头碱合成刺乌头碱氢溴酸盐的方法. 用元素分析、红外光谱、高分辨质谱和核磁共振进行了表征. 并用X射线单晶衍射确定了标题化合物的绝对构型. 晶体结构表明, 该化合物通过分子间氢键形成了网状类似超分子结构. 晶体属于单斜晶系, P2₁空间群, 晶胞参数: a＝1.0619(2) nm, b＝1.2196(3) nm, c＝1.2282(2) nm, β＝90.87(1)°, V＝1.59037(54) nm³, Z＝2, D_m＝1.428 g/cm^－3, F(000)＝720.0, µ＝1.349 mm^－1. 环 A, B, C, D, E和F分别呈船式、椅式、信封式、船式、船式和信封式. 其绝对构型被确定为1S,4S,5S,7S,8S,9S,10S,11S,13R,14S,16S,17R.     

Photochemical reaction mechanism of cyclobutanone: CASSCF study

The photochemical reaction channels of cyclobutanone have been studied at the CASSCF level with a 6‐31G* basis set. Starting from the n‐π* excited‐state (S₁) cyclobutanone, the three reactions can take place: decarbonylation (produce CO and cyclopropane or propylene), cycloelimination (produce ketene and ethylene), and ring expansion (produce oxacarbene). Our computation indicates that decarbonylation products CO and triplet trimethylene are formed on the triplet n‐π* excited state (T₁) in a stepwise way via a biradical intermediate after intersystem crossing (ISC) to T₁ from S₁. And, then, the triplet trimethylene undergoes a second ISC to the ground state (S₀) to produce the singlet trimethylene from which cyclopropane can be produced rapidly only overcoming a 1 to 2‐kcal/mol barrier while propylene can be formed as a secondary product. The cycloelimination products ketene and ethylene are formed on the S₀ in a concerted mechanism after internal conversion (IC) to S₀ from S₁ via a biradical conical intersection. The reaction channels corresponding to ring expansion on the S₀, T₁, and S₁ states have also been discussed, and the likeliest reaction path is that oxacarbene is formed on the ground state following S₁/S₀ internal conversion. The surface topology of cyclobutanone on the S₁ surface is characterized by a transition state separating the minimum from the S₁/S₀ conical intersection, which is consistent with the previous computations and can explain the wavelength dependence of the fluorescence emission yield. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Mechanistic Insights into the Photophysics of Ortho-hydroxyl GFP Core Chromophores

Herein we have employed the MS-CASPT2//CASSCF method to study the S₁ excited-state intramolecular proton transfers (ESIPTs) of recently synthesized ortho-hydroxyl GFP core chromophores, i.e. OHIM, CHBDI, and MHBID, and their excited-state relaxation pathways. We have found that in OHIM and CHBDI, the ESIPT process is associated with small barriers of 3.4 and 4.2 kcal/mol; while, in MHBDI, it becomes essentially barrierless. Moreover, we have found two main S₁ excited-state radiationless channels. In the first one, the enol S₁ species decays to the S₀ state via the enol S₁/S₀ conical intersection after overcoming considerable barriers of 7.0 and 7.7 kcal/mol in OHIM and CHBDI (however, in MHBDI, it is nearly barrierless). In the second one, the keto S₁ species is first generated through the ESIPT event; then, it is de-excited into the S₀ state in the vicinity of the keto S₁/S₀ conical intersection. These energetically allowed excited-state decay channels rationalize experimentally observed ultralow fluorescence quantum yields. The insights gained from the present work may help to guide the design of new ortho-hydroxyl GFP core chromophores with improved fluorescence emission and brightness.     

Spectroscopic Properties of Morin in Various CH3OH–H2O and CH3CN–H2O Mixed Solvents

The specific fluorescence properties of morin (3,2′,4′,5,7‐pentahydroxyflavone) were studied in various CH₃OH–H₂O and CH₃CN–H₂O mixed solvents. Although the dihedral angle is large in the S₀ state, morin has an almost planar molecular structure in the S₁ state owing to the very low rotational energy barrier around the interring bond between B and the A, C ring. The excited state intramolecular proton transfer (ESIPT) at the S₁ state cannot occur immediately after excitation, S₁ → S₀ fluorescence can be observed. Two conformers, Morin A and B have been known. At the CH₃OH–H₂O, Morin B will be the principal species but at the CH₃CN–H₂O, Morin A is the principal species. At the CH₃OH–H₂O, owing to the large Franck–Condon (FC) factor for S₂ → S₁ internal convernal (IC) and flexible molecular structure, only S₁ → S₀ fluorescence was exhibited. At the CH₃CN–H₂O, as the FC factor for S₂ → S₁ IC is small and molecular structure is rigid, S₂ → S₀ and S₁ → S₀ dual fluorescence was observed. This abnormal fluorescence property was further supported by the small pK₁ value, effective delocalization of the lone pair electrons of C(2′)–OH to the A, C ring, and a theoretical calculation.