Density functional theory study on the reactions of X− with CH3SY (X,Y = F,Cl, Br,I)

Gas‐phase anionic reactions X^? + CH₃SY (X, Y = F, Cl, Br, I) have been investigated at the level of B3LYP/6‐311+G (2df,p). Results show that the potential energy surface (PES) of gas‐phase reactions X^? + CH₃SY (X, Y = Cl, Br, I) has a quadruple‐well structure, indicating an addition–elimination (A–E) pathway. The fluorine behaves differently in many respects from the other halogens and the reactions F^? + CH₃SY (Y = F, Cl, Br, I) correspond to deprotonation instead of substitution. The gas‐phase reactions X^? + CH₃SF (X = Cl, Br, I), however, follow an A–E pathway other than the last two out going steps (COM2 and PR) that proceeds via a deprotonation. The polarizable continuum model (PCM) has been used to evaluate the solvent effects on the energetics of the reactions X^? + CH₃SY (X, Y = Cl, Br, I). The PES is predicted to be unimodal in the solvents of high polarity. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Theoretical study of the gas‐phase SN2 reactions of X− with CH3OY (X,Y = Cl,Br, I)

The gas‐phase nucleophilic substitution reactions at saturated oxygen X^? + CH₃OY (X, Y = Cl, Br, I) have been investigated at the level of CCSD(T)/6‐311+G(2df,p)//B3LYP/6‐311+G(2df,p). The calculated results indicate that X^? preferably attacks oxygen atom of CH₃OY via a S_N2 pathway. The central barriers and overall barriers are respectively in good agreement with both the predictions of Marcus equation and its modification, respectively. Central barrier heights (ΔH and ΔH) correlate well with the charges (Q) of the leaving groups (Y), Wiberg bond orders (BO) and the elongation of the bonds (O? Y and O? X) in the transition structures. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

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.     

Theoretical study and rate constants calculation for the reactions X + CF3CH2OCF3 (X = F,Cl, Br)

The multiple‐channel reactions X + CF₃CH₂OCF₃ (X = F, Cl, Br) are theoretically investigated. The minimum energy paths (MEP) are calculated at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD (single‐point) method. The rate constants for major reaction channels are calculated by canonical variational transition state theory (CVT) with small‐curvature tunneling (SCT) correction over the temperature range 200–2000 K. The theoretical three‐parameter expressions for the three channels k_1a(T) = 1.24 × 10^?15T^1.24exp(?304.81/T), k_2a(T) = 7.27 × 10^?15T^0.37exp(?630.69/T), and k_3a(T) = 2.84 × 10^?19T^2.51 exp(?2725.17/T) cm³ molecule^?1 s^?1 are given. Our calculations indicate that hydrogen abstraction channel is only feasible channel due to the smaller barrier height among five channels considered. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2012     

Definitive ab initio studies of model SN2 reactions CH(3)X+F- (X=F,Cl, CN,OH, SH,NH(2), PH(2))

The energetics of the stationary points of the gas-phase reactions CH(3)X+F(-)-->CH(3)F+X(-) (X=F, Cl, CN, OH, SH, NH(2) and PH(2)) have been definitively computed using focal point analyses. These analyses entailed extrapolation to the one-particle limit for the Hartree-Fock and MP2 energies using basis sets of up to aug-cc-pV5Z quality, inclusion of higher-order electron correlation [CCSD and CCSD(T)] with basis sets of aug-cc-pVTZ quality, and addition of auxiliary terms for core correlation and scalar relativistic effects. The final net activation barriers for the forward reactions are: E (b/F,F)=-0.8, E (b/F, Cl)=-12.2, E (b/F,OH)=+13.6, E b/F,OH=+16.1, E b/F,SH=+2.8, Eb/F, NH=+32.8, and E b/F,PH =+19.7 kcal x mol(-1). For the reverse reactions E b/F,F= -0.8, Eb/Cl,F =+18.3, E b/CN,F=+12.2, E b/OH,F =-1.8, E b/SH,F =+13.2, E b/NH(2),=-1.5, and E b/PH(2) =+9.6 kcal x mol(-1). The change in energetics between the CCSD(T)/aug-cc-pVTZ reference prediction and the final extrapolated focal point value is generally 0.5-1.0 kcal mol(-1). The inclusion of a tight d function in the basis sets for second-row atoms, that is, utilizing the aug-cc-pV(X+d)Z series, appears to change the relative energies by only 0.2 kcal x mol(-1). Additionally, several decomposition schemes have been utilized to partition the ion-molecule complexation energies, namely the Morokuma-Kitaura (MK), reduced variational space (RVS), and symmetry adapted perturbation theory (SAPT) techniques. The reactant complexes fall into two groups, mostly electrostatic complexes (FCH(3).F(-) and ClCH(3).F(-)), and those with substantial covalent character (NCCH(3).F(-), CH(3)OH.F(-), CH(3)SH.F(-), CH(3)NH(2).F(-) and CH(3)PH(2).F(-)). All of the product complexes are of the form FCH(3).X(-) and are primarily electrostatic.     

Identity SN2 reactions X- + CH3X --> XCH3 + X- (X=F, Cl, Br, and I) in vacuum and in aqueous solution: a valence bond study

The recently developed (L. Song, W. Wu, Q. Zhang, S. Shaik, J. Phys. Chem. A 2004, 108, 6017) valence bond method coupled with a polarized continuum model (VBPCM) has been applied to the identity SN2 reaction of halides in the gas phase and in aqueous solution. The barriers computed at the level of the breathing orbital VB method (P. C. Hiberty, J. P. Flament, E. Noizet, Chem. Phys. Lett. 1992, 189, 259), BOVB and VBPCM//BOVB, are comparable to CCSD(T) and CCSD(T)//PCM results and to experimentally derived barriers in solution (W. J. Albery, M. M. Kreevoy, Adv. Phys. Org. Chem. 1978, 16, 85). The reactivity parameters needed to apply the valence bond state correlation diagram (VBSCD) method (S. Shaik, J. Am. Chem. Soc. 1984, 106, 1227), were also determined by VB calculations. It has been shown that the reactivity parameters along with their semiempirical derivations provide a satisfactory qualitative and quantitative account of the barriers.     

Photochemical Generation of Chiral N,B,X‐Heterocycles by Heteroaromatic C−X Bond Scission (X=S,O) and Boron Insertion

Chiral organoboron compounds with a chelate backbone and mesityl/heterocycle substituents (thienyl, furyl, and derivatives thereof) undergo a quantitative phototransformation that yields rare, chiral N,B,X‐containing heterocycles, such as base‐stabilized 1,2‐thiaborinines and 1,2‐oxaborinines. Boriranes were observed as intermediates in some of these transformations. The oxaborinines display further reactivity, generating 4a,12b‐dihydrobenzo[h][1,2]oxaborinino[4,3‐f]quinolines through a sequential conrotatory electrocyclization and a [1,5]‐H shift. The N,B,X‐containing heterocycles display strong blue‐green to orange‐red emission in the solid state. Combined DFT//CASP2T calculations suggest that a common biradical intermediate is responsible for the formation of these compounds as well as their interconversion.     

Thermodynamic and Kinetic Studies on the SiH + XH_3 (X=N, P) Reactions

Silicon chemistry has been attracted more attention because of its applications to the production of thin silicon films and the etching of silicon wafers in micro-electronics1. Silylidyne (SiH), which plays an important role in plasma chemical vapor deposition (CVD) processes, has been investigated in experimental research2-5. The reaction mechanism of SiH insertion reaction with small molecules such as XH3 (X=N, P) was recently studied by means of M豯ler-Plesset perturbation theory6.…     

Ligand and substrate effects in gas-phase reactions of NiX(+)/RH couples (X=F, Cl, Br, I; R=CH3, C2H5, nC3H7, nC4H9)

The reactions of small saturated hydrocarbons by gaseous nickel cations NiX+ (X=F, Cl, Br, I) are investigated by means of electrospray ionization mass spectrometry. The halide cations are obtained from solutions of the corresponding Ni(II) salts in water or methanol as solvents. NiF+ is the only Ni(II) halide complex that brings about thermal activation of methane. The branching ratios of the observed reactions with C2H6, C3H8, and nC4H10 are shifted systematically by changing the nature of both the ligand X and the substrate RH. In the elimination of HX (X=F, Cl, Br, I), the formal oxidation state of the metal ion appears to be conserved, and the importance of this reaction channel decreases in going from NiF+ to NiI+. A reversed trend is observed in the losses of small closed-shell neutral molecules, that is, H2, CH4 and C2H6, which dominate the gas-phase ion chemistry of NiI+/RH couples. Additionally, inner-sphere electron-transfer reactions take place for a few systems, that is, the delivery of hydride or methanide ions from the hydrocarbon to NiX+ in the course of which the hydrocarbon is converted to a carbenium ion and the cationic metal complex gives rise to a neutral RNiX molecule (R=H, CH3). This process gains importance with decreasing atomic number of the halides and with increasing the size of the alkane. Thus, it constitutes the major pathway in the reactions of NiF+ with propane and n-butane, whereas it is not observed for any of the NiI+/RH couples investigated. Concerning the regioselectivity of the reactions with propane and n-butane, heterolytic cleavage of secondary carbon--hydrogen bonds is clearly preferred compared to that of primary ones, as revealed by deuterium labeling studies. For the NiF+/C3H8 couple, the selectivity of the hydride transfer is as large as 360 in favor of the secondary positions. Though smaller, large preferences for the activation of secondary C--H bonds are also operative in homolytic bond activation of RH (R=nC3H7, nC4H9).     

Ag(PPh3)nX(n=1,2,3；X=Cl,Br,I)的电化学合成

银配合物;;三苯基膦;电合成;Ag(PPh3)nX(n=1;2;3；X=Cl;Br;I)的电化学合成     

Comparative Computational Study of Hydrogen Abstraction Reactions of CY3H + XO− (X,Y = F,Cl, and Br)

The effects of halogen substituents on the reactivity are characterized by the hybrid B3LYP and BHandHLYP functionals of density functional theory using the aug‐cc‐pVDZ basis set. The species XO⁻ and CY₃H, where X, Y = F, Cl, and Br, have been chosen as model reactants in this work. Also, the mechanism of the hydrogen abstraction (HAT) reaction has been used to study the chemical reactivity of these anionic reactions. Our theoretical findings suggest that the relative reactivity of the CY₃H + XO⁻ reactions increases as Y goes from F to Br and decreases as X goes from F to Br. Moreover, among all reactions investigated in this study, the special role of the Y has very dominant effect on activation of the C–H bond in CY₃H when XO⁻ attacks the CY₃H. Again, through the transition state theory the rate constants at 298–1000 K are also evaluated for the HAT reactions, indicating the lower the temperature the faster is the chemical reaction.     

Fe+与CH3X（X=Cl,Br,I）反应的理论研究

铁及其复合物催化的C—X键功能化日益引起人们的重视.采用密度泛函理论(DFT),在B3LYP/def2-SVP水平下详细研究了Fe+与CH3X(X=Cl,Br,I)的反应活性和机理.计算结果表明标题反应存在两种反应机制,即插入机制和SN2机制.从机理上来看,在插入机理中,反应都始于Fe+离子从侧面进攻CH3X,生成产物FeX+和CH3;而在SN2机制中,反应则始于Fe+离子从背后进攻CH3X,生成产物3FeCH+和X.从我们的计算可以看出,四重态或六重态下的Fe+离子在C—X键活化中展现了截然不同的催化活性;在所有通道中,都以四重态为主导;SN2机制中相对较高的决速能垒使其丧失了竞争性.再者,计算表明在所有的插入机制中,所有通道都是放热的,而在SN2机制中,仅有X=I时,反应是放热的.此外,计算表明这些反应属于两态反应活性,两种机制中,在反应的入口和出口存在最小能量交叉点.此外,反应途径电子结构追踪分析表明自旋极化对能量影响较大,调控着反应采取的反应通道和主副产物比例.通过本文的理论研究,尤其是详细的电子结构分析,为铁催化剂活化C—X键和C—C耦联反应提供了线索和以铁为基的催化剂设计提供理论依据.     

苯-卤素(X2, X=F, Cl, Br, I)相互作用本质的对称性匹配微扰理论研究

在MP2水平下对被定义为"电荷转移复合物(CTC)"的苯(C6H6)-卤素分子X2(X＝F, Cl, Br, I)相互作用体系进行了量子化学研究. 在优化所得C6H6-X2(X＝F, Cl, Br, I)复合物的平衡几何结构中, 卤素分子X2接近垂直指向苯环上碳-碳双键的中心. 自然键轨道(NBO)分析结果表明, 苯-卤素体系中电荷转移的数量很少. 对称性匹配微扰理论(Symmetry-adapted perturbation theory, SAPT) 能量分解结果显示, 在4个复合物体系中, 静电作用的贡献相对较小(只占总吸引作用的20%左右), 对于C6H6-F2体系, 色散作用是其主要吸引作用, 对于C6H6-Cl2, C6H6-Br2和C6H6-I2 体系, 诱导作用则是其主要的吸引作用, 从F到I, 色散作用逐渐减弱, 诱导作用逐渐增强, 表明在电子相关水平上将苯-卤素体系称为"电荷转移复合物"的说法并不确切.     

Exceedingly Facile PhX Activation (X=Cl,Br, I) with Ruthenium(II): Arresting Kinetics,Autocatalysis, and Mechanisms

[(Ph₃P)₃Ru(L)(H)₂] (where L=H₂ ( 1 ) in the presence of styrene, Ph₃P ( 3 ), and N₂ ( 4 )) cleave the Ph? X bond (X=Cl, Br, I) at RT to give [(Ph₃P)₃RuH(X)] ( 2 ) and PhH. A combined experimental and DFT study points to [(Ph₃P)₃Ru(H)₂] as the reactive species generated upon spontaneous loss of L from 3 and 4 . The reaction of 3 with excess PhI displays striking kinetics which initially appears zeroth order in Ru. However mechanistic studies reveal that this is due to autocatalysis comprising two factors: 1) complex 2 , originating from the initial PhI activation with 3 , is roughly as reactive toward PhI as 3 itself; and 2) the Ph? I bond cleavage with the just‐produced 2 gives rise to [(Ph₃P)₂RuI₂], which quickly comproportionates with the still‐present 3 to recover 2 . Both the initial and onward activation reactions involve PPh₃ dissociation, PhI coordination to Ru through I, rearrangement to a η²‐PhI intermediate, and Ph? I oxidative addition.     

Au(II)化合物[Au(CH2)2PH2]2X2 (X＝F, Cl, Br, I)的量子化学理论研究

采用从头计算HF, MP2方法和密度泛函理论, 对Au(II)系列化合物[Au(CH₂)₂PH₂]₂X₂ (X＝F, Cl, Br, I)的几何结构、电子结构和振动频率进行了研究. 研究表明Au的5d和6s电子参与Au—Au以及Au—X之间的成键. Au—Au, Au—X键强烈的电子相关作用使HF方法不适于该体系的研究, BP86和B3LYP两种泛函给出较大的Au—Au和Au—X键长, 而MP2方法和局域的密度泛函方法则给出了合理的结构参数. 局域密度泛函方法计算得到的Au—Au键和 Au—X键振动频率也与实验数据符合较好. 还运用含时密度泛函理论计算了[Au(CH₂)₂PH₂]₂X₂的电子激发能, 对分子在紫外-可见光谱范围内的电子跃迁进行了分析, 考察了卤素配体对激发能的影响, 并结合分子轨道能级的变化对此给予了解释.     

Halogen Bonding or Hydrogen Bonding between 2,2,6,6-Tetramethyl-piperidine-noxyl Radical and Trihalomethanes CHX3 (X=Cl,Br, I)

The halogen and hydrogen bonding complexes between 2,2,6,6-tetramethylpiperidine-noxyl and trihalomethanes (CHX₃, X=Cl, Br, I) are simulated by computational quantum chem-istry. The molecular electrostatic potentials, geometrical parameters and interaction energy of halogen and hydrogen bonding complexes combined with natural bond orbital analysis are obtained. The results indicate that both halogen and hydrogen bonding interactions obey the order Cl相似文献   

C6F5X＋（X=Cl,Br,I,CH3）离子的理论研究

用DFT B3LYP方法及6-311G（d,p）,6-311＋G（d,p）和LanL2dz基组,对C6F5X＋（X=Cl,Br,I,CH3）阳离子做了理论研究,优化了它们的电子基态的构型,计算了对应分子的垂直电离势（VIP）和绝热电离势（AIP）.结果表明四种离子的构型的对称点群和对应分子相同,但构型参数有明显差别.B...     

Mechanistic Aspects of the Holmium‐Mediated,Reciprocal Hydrogen/Sulfur Exchange in the Gas Phase: C6H5CH3+CH2S→C6H5CHS+CH4

The thermal reaction of [Ho(CH₂S)]⁺ with toluene giving rise to [C₆H₅CHSHo]⁺ and CH₄ has been investigated using Fourier‐transform ion cyclotron resonance (FT‐ICR) mass spectrometry complemented by density functional theory (DFT) calculations. The high reactivity of [Ho(CH₂S)]⁺ which is in distinct contrast with the non‐reactivity of “bare” Ho⁺ has its origin in the presence of a carbon‐centered radical; the latter initiates hydrogen‐atom abstraction from the methyl group of toluene as the first step of a sequence of hydrogen and sulfur transfer mediated by cationic holmium.