HNCS与Cl原子的反应机理及电子密度拓扑分析

在QCISD(T)/6-311++G(d,p)和B3LYP/6-311++G(d,p)级别上研究了HNCS与Cl原子的反应机理. 并应用经典过渡态理论和正则变分过渡态理论结合小曲率隧道效应, 计算了200-2500 K温度范围内各反应通道的速率常数. 结果表明, HNCS与Cl原子反应存在3个反应通道. 当温度低于294 K时, 生成HCl+NCS的夺氢反应(a)是优势通道, 温度高于294 K时, 生成HNC(Cl)S的加成反应(c)为主反应通道, Cl进攻N的反应通道(b)因能垒较高而难以进行.     

卤素离子与卤代苯气相SNAr反应理论研究

采用B3LYP/6-311+G**和MP2/6-311+G**方法,研究了卤素离子与卤代苯气相SNAr反应(Ar Y+X-=Ar X+Y-,X,Y=F,Cl,Br和I)。结果显示,气相里除了X=Y=F反应为分步路径外,其余反应通道都是协同SNAr机理;F离子进攻卤苯SNAr反应无论从动力学(总能垒ΔGb=9.0~17.3 k J/mol)还是热力学上来说都很容易进行,然而Cl、Br和I离子进攻的反应,其MP2吉布斯自由能垒(ΔGb)高达91.3~202.5 k J/mol,因此在气相里很难发生;另外,标题反应的反应性可以通过卤素离子质子亲和能(PA)、最高占据轨道能(EHOMO)、Mulliken电负性(χ)以及Wiberg键级(BO)与NPA电荷(Q)来分析,其中,过渡态里C─Y键的断裂是引起反应能垒升高的主要因素,亲核试剂的亲核能力主要由EHOMO控制,而卤素离子的离去能力由其PA或χ决定。     

CH2X(X=H,F,Cl)与臭氧反应机理的量子化学研究

用量子化学UMP2方法,在6-311++G**基组水平上研究了CH2X(X=H,F,Cl)与臭氧反应机理,全参数优化了反应过程中反应物、中间体、过渡态和产物的几何构型,在UQCISD(T)/6-311++G**水平上计算了它们的能量,并对它们进行了振动分析,以确定中间体和过渡态的真实性.从CH2X(X=H,F,Cl)与O3的反应机理的研究结果看,它们与O3反应的活性都比较强,相对而言,活性大小顺序为CH2F＞CH3＞CH2Cl,也就是说,CH2F自由基与臭氧间的反应活性最强,对大气臭氧的损耗将是最大的.同时研究还发现CH2X(X=H,F,Cl)系列自由基与O3的反应都是强放热反应.     

氮原子与卤代甲烷反应的直接氢抽提过程研究

利用B3LYP理论研究了N(~4S)+CH_3X(X = H, F, Cl)反应体系的直接氢抽提过 程,分别得到了各反应物、产物和过渡态的优化构型和谐振频率。同时应用了6- 31G(d), 6-311+G(d,p)和6-311+ + G(2d,2p)基组,考察其大小对反应体系中各物 种构型及能量的影响。理论计算表明,随着基组的增加,反应势垒逐渐降低,反应 吸热减少。对比取代甲烷的情形,结果表明反应过程中卤素原子具有典型的诱导效 应,降低了抽提势垒。     

真空下X2 (X=Cl、Br)与AgOCN气-固反应机理

在真空条件下完成了X2 (X=Cl、Br)与AgOCN间的气-固异相反应，利用紫外光电子能谱（PES）仪，探测与确定反应产物是XNCO (X=Cl、Br)，并推断其可能为一过渡态反应，生成中间络合物，新键产生与旧键断裂同时进行.     

传统氢键(X—H…Y)还是X—H…π相互作用？ ——无机苯与卤化氢相互作用本质的量子化学研究

在MP2/6-311＋＋G**水平对无机苯(B3N3H6)与卤化氢HX (X＝F, Cl, Br, I)相互作用体系进行了系统研究. 结果表明在B3N3H6-HX (X＝F, Cl, Br, I)体系的平衡几何结构中, HX的H原子倾向于指向B3N3H6环上的N原子, 且从HF到HI相互作用强度依次减弱. 与苯-卤化氢体系比较, 除与HF相互作用B3N3H6较C6H6强外, 其余体系B3N3H6均较C6H6弱(结合能数值相差4 kJ/mol左右). 对称匹配微扰理论(SAPT)能量分解结果说明静电、诱导和色散力对描述B3N3H6-卤化氢体系的相互作用都很重要, 从HF到HI静电能占总吸引作用能的百分比逐渐减少, 色散能占总吸引作用能的百分比逐渐增加, 这种变化趋势与苯-卤化氢体系比较类似, 表明B3N3H6与卤化氢的相互作用随着卤素原子序数的递增, 传统氢键作用趋势减弱, X—H…π相互作用趋势增强.     

HCCO自由基与LiX(X=F,Cl,Br)锂键复合物的从头算研究

在MP2/6-311++G**水平上优化乙烯酮自由基与LiX(X=F,Cl,Br)形成锂键复合物.当卤素的电负性很强(如F元素),使得Li原子处于缺电子状态,此时,电子给体会把电子偏移向锂,形成共价性较强的锂键.而当卤素的电负性减弱时,锂键中主要成分逐渐变为离子键,并且此时锂键性质还要受电子给体影响.另外,由于HCCO为缺电子结构,电负性较弱且体积较大的卤素中的孤对电子会与HCCO之间通过静电相互作用,使得HCCO…Li—X键夹角变小,接近120°.锂键性质对HCCO…LiX(X=F,Cl,Br)复合物中Li—X的伸缩振动频率有直接影响.当锂键表现为共价性时,该频率红移,而当锂键表现为离子性时,该频率蓝移.但是,由于Cl的电负性与O的接近,C的电负性与Br接近所以,在O…Li…Cl和C…Li…Br中容易形成共振结构,导致远大于在其他复合物中的红移.     

CH_2X(X=H,FCI)与臭氧反应机理的最子化学研究

用量化学UMP2方法，在6-311++G**基组水平上研究了CH_2X(X=H,FCI)与臭氧反 应机理，全参数优化了反应过程中反应物、中间体、过渡态和产物的内何构型，在 UQCISD（T）/6-311++G**水平上计算了它们的能量，并对它们进行了振动分析，以 确定中间体和过渡态的直实性。从CH_2X(X=H,FCI)与O_3的反应机理的研究结果看 ，它们与O_3反应的活性都比较强，相对而言，活性大小顺序为CH_2F＞CH_3＞ CH_2CI，也就是说，CH_2F自由基与臭氧间的反应活性最强，对大气臭氧的损耗将 是最大的。同时研究还发现CH_2X(X=H,FCI)系列自由基与O_3的反应都是强放热反 应。     

CH_2X(X=H,FCI)与臭氧反应机理的最子化学研究

用量化学UMP2方法，在6-311++G**基组水平上研究了CH_2X(X=H,FCI)与臭氧反 应机理，全参数优化了反应过程中反应物、中间体、过渡态和产物的内何构型，在 UQCISD（T）/6-311++G**水平上计算了它们的能量，并对它们进行了振动分析，以 确定中间体和过渡态的直实性。从CH_2X(X=H,FCI)与O_3的反应机理的研究结果看 ，它们与O_3反应的活性都比较强，相对而言，活性大小顺序为CH_2F＞CH_3＞ CH_2CI，也就是说，CH_2F自由基与臭氧间的反应活性最强，对大气臭氧的损耗将 是最大的。同时研究还发现CH_2X(X=H,FCI)系列自由基与O_3的反应都是强放热反 应。     

HNCO与CX（X=F，Cl，Br）自由基反应机理的密度泛函理论研究

用量子化学密度泛函理论的B3LYP方法,在6-31+G~*水平上按BERNY能量梯度解 析全参数优化了HNCO与CX（X=F,Cl,Br）反应势能面上各驻点的几何构型,通过 振动频率分析确认了中间体和过渡态,内禀反应坐标（IRC）对反应物、中间体、 过渡态和产物的相关性予以证实,对各驻点进行了零点能校正（ZPE）在此基础上 计算了反应能垒。研究结果表明,与HNCO和其它小分子自由基反应不同,HNCO与 CX自由基反应首先发生分子间H原子迁移,随后N与CX的C（1）原子相互靠近成键并 生成较稳定的中间体,再发生N-C（2）键的断裂,完成N向C（1）上的迁移并进一 步解离为产物。反应按反应物→TS1→IM→TS2→产物通道进行。反应为放热反应。     

Topological characteristics of electron density distribution in SSXY --> XSSY (X or Y = F, Cl, Br, I) isomerization reactions

The reactions of SSXY to XSSY (X or Y = F, Cl, Br, I) have been studied at B3LYP/6-311++G(2df) and MP2/6-311++G(2df) levels based on B3LYP/6-311++G(2df) optimized geometries. There are two pathways (X or Y atom transferring) for each reaction of SSXY to XSSY(X or Y = F, Cl, Br, I). The "Atoms in Molecules" theory has been applied to analyze the topological characteristics of electron density distribution along the reaction path. (a) The S-S-X or S-S-Y ring structure transition region (STR) is contributed to S(1)-X or S(1)-Y bond formation and S(2)-X or S(2)-Y bond annihilation. The STR and structure transition state (STS) are defined. (b) Comparing the two pathways of each SSXY --> XSSY (X, Y = F, Cl, Br, I) reaction, X or Y atom transferring, the broader the STR is, the later the STS appears, and the pathway is easier. (c) When X linked to the same S site of a three-member ring (S-S-F, S-S-Cl, S-S-Br, or S-S-I), the ring STR becomes broader and the STS appears later according to the sequence of X = F, Cl, Br, and I. And in these cases, for exothermic reactions, the higher the DeltaE(P-->TS1) is, the broader the STR is and the later the STS appears. (d) When the same Y atom linked to different three-member-ring S-S-X, the STR becomes broader and the STS appears later according to the sequence of X = F, Cl, Br, and I in the ring. And in these cases, for exothermic reactions, the lower the DeltaE(P-->TS2) is, the broader the STR is and the later the STS appears.     

Communication: probing the entrance channels of the X+CH4→HX+CH3 (X = F, Cl, Br, I) reactions via photodetachment of X(-)-CH4

The entrance channel potentials of the prototypical polyatomic reaction family X + CH(4) → HX + CH(3) (X = F, Cl, Br, I) are investigated using anion photoelectron spectroscopy and high-level ab initio electronic structure computations. The pre-reactive van der Waals (vdW) wells of these reactions are probed for X = Cl, Br, I by photodetachment spectra of the corresponding X(-)-CH(4) anion complex. For F-CH(4), a spin-orbit splitting (～1310 cm(-1)) much larger than that of the F atom (404 cm(-1)) was observed, in good agreement with theory. This showed that in the case of the F-CH(4) system the vertical transition from the anion ground state to the neutral potentials accesses a region between the vdW valley and transition state of the early-barrier F + CH(4) reaction. The doublet splittings observed in the other halogen complexes are close to the isolated atomic spin-orbit splittings, also in agreement with theory.     

Structures and electronic properties of Al7x0,- and Al13 X1,2,12- clusters with X=F, Cl, and Br

The structures, binding energies, and electronic properties for Al7X, Al7X-, Al13X-, Al13X2-, and Al13X12- (X = F, Cl, Br) were studied at the B3LYP/6-311+G(2d,p) level. Among the systems studied, Al7 and Al13 clusters in Al7X and Al13X- reveal alkali-like and halogen-like superatom characters, respectively. Al7 can bind with one halogen atom to form a salt-like compound as Al7+delta-X-delta. Al13- can combine with one halogen atom to form a diatomic halogen anion Al13X-. However, when adding more halogens, the superatom structure would be destroyed, resulting in low-symmetry compounds with the center Al atom moving toward the cluster surface. The structures of Al13X1,2,12- (X = F, Cl, Br) are similar to those of X = I; however, their binding energies and electron structures are much different. In addition, the analyses of the calculated NBO charges show that Cl and Br have similar properties, but much different from F, when interacting with the Al clusters. The Al-Cl and Al-Br bonds have more covalent character in Al7X and Al13X2,12-, in contrast to the corresponding Al-F bond, which has prominent ionic character.     

CH3SS与XO (X＝F,Cl, Br)反应过程的电子密度拓扑研究

利用MP2/6-311＋＋G(d,p)//B3LYP/6-311＋＋G(d,p)对CH3SS与XO (X＝F, Cl, Br)的反应机理进行了研究. 着重从电子密度拓扑分析角度讨论了化学键的生成和断裂. 计算结果表明单线态反应为主要反应通道, 且由于该通道的反应能垒低、放热明显, 说明CH3SS与XO在大气中比较容易进行. 电子密度拓扑分析表明, 在单线态抽氢反应通道中存在着四元环状过渡结构, 随着反应进行, 此四元环状过渡结构通过一个T-型结构变为三元环状过渡结构, 最后环状结构消失得到产物.     

OXO(X=Cl,Br)与H(2S)反应机理的量子化学研究

卤素二氧化物自由基(OXO)是重要的同温层物种，在极地的夜间含量尤其丰富，由于其光解产生的卤素原子会造成臭氧的严重损耗，因此愈来愈受到人们的广泛关注嘲．OXO自由基可以通过自由基之间的反应或微波放电等方式获得，有关它与其它大气物种的反应已经进行了许多研究，Bemand等在实验上研究了Cl，H，O与OClO的反应动力学，对于OBrO与H之间的反应目前尚未见实验研究的报道，只有Guhua等在理论上对部分XBrO2(X=H，Cl，Br)同分异构体进行了研究．     

硫原子上亲核取代反应的密度泛函理论研究

在B3LYP/6-311 G(2df,p)的水平上,对反应X- CH3SCl(X=F,Cl,Br,I)进行了理论研究.计算结果表明:X-(X=Cl,Br,I)与CH3SCl作用时,实际发生的是在硫原子上而不是在碳原子上的亲核取代反应,而且属于加成-消去机理.但是F-与CH3SCl作用则容易发生脱质子反应.     

An electron localization function and catastrophe theory analysis on the molecular mechanism of gas-phase identity SN2 reactions

A set of four reactions, XCH₃+X^? (X=F, Cl, Br) and ClSiH₃+Cl^?, is investigated by means of the joint use of the electron localization function (ELF) and catastrophe theory (CT) analysis in order to obtain new insights into the bond breaking/forming processes for identity S_N2 gas-phase reactions. Using DFT calculations at the OLYP/6-311++G(d,p) level, the effect of nucleophile (F, Cl, and Br anions) and the role of reacting centers (C or Si) on the reaction mechanisms are investigated. The charge-shift character of carbon–halogen bonds is studied by determination of the weights of the Lewis resonance structures. In all S_N2 reactions at the carbon atom, there is a progressive reduction on the covalent character of the C–X bond from the reactant complex (0.41, 0.57, 0.58 for F, Cl, and Br, respectively) until the bond-breaking process, occurring before the transition structure is reached. On the other hand, the Si–Cl bond maintains its degree of covalent character (0.51) from the isolated fragments to the formation of a stable transition complex, presenting two silicon–chlorine charge-shifted bonds. The analysis of the ELF topology along the reaction path reveals that all reactions proceed via the same turning points of fold-type but the order is inverted for reactions taking place at C or Si atoms.     

N(4S)+CH3X(X=Cl、Br)反应机理的理论研究

The reaction of N(4S)+CH3X(X=Cl、Br) was studied by the ab initio method. The geometries of the reactants, transition states and products were optimized at the MP2/6-311+G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single-point calculations for all the stationary points were carried out at the MP2/6-311++G(3df,2p) and the QCISD(T)/6-311+G(d,p) levels using the MP2/6-311+G(d,p) optimized geometries. The energies of all the stationary points were calculated by the G2MP2 method. The results of this theoretical study indicate that the reaction has three reaction channels: H abstraction reaction channel a, Cl or Br abstraction reaction channel b and substitution reaction channel c. For the N(4S)+CH3Cl reaction, reaction channel a is the main reaction channel. Reaction channels b and c may have a slight contribution in the reaction. For the N(4S)+CH3Br reaction, reaction channel a is the main reaction channel. Reaction channels b and c may have some contribution in the reaction.