Ab initio molecular orbital investigation of the amine-alanes (CH(3))(n)H(3)(-)(n)AlNX(3) and phosphane-alanes (CH(3))(n)H(3)(-)(n)AlPX(3) (X = H, F, and Cl; n = 0-3) complexes

We report on ab initio calculations at the G2(MP2) level of the structures and Al-N(P) bond complexation energies of the (CH(3))(n)H(3)(-)(n)AlNX(3) and (CH(3))(n)H(3)(-)(n)()AlPX(3) (X = H, F, and Cl; n = 0-3) donor-acceptor complexes. For the (CH(3))(3)AlNX(3) and (CH(3))(3)AlPX(3) complexes, the C(3)(v) symmetry is found to be favored, and for the other complexes the C(s) symmetry is found to be favored. The G2(MP2) calculated complexation energies show for the amine ligands the trend NH(3) > NCl(3) > NF(3). A similar trend PH(3) approximately PCl(3) > PF(3) is predicted for the phosphane ligands. The NBO partitioning scheme shows that there is no correlation between the stability and the charge transfer.     

Schwingungsspektren der Vinylmethylhalosilane H2C = CH(CH3)3−nSiXn (n = 1,2; X = F,Cl)

Ohne Zusammenfassung     

Theoretical study of (CH...C)- hydrogen bonds in CH(4-n)X(n) (X = F, Cl; n = 0, 1, 2) systems complexed with their homoconjugate and heteroconjugate carbanions

This work deals with a theoretical study of the (CH...C)- hydrogen bonds in CH4, CH3X, and CH2X2 (X = F, Cl) complexed with their homoconjugate and heteroconjugate carbanions. The properties of the complexes are calculated with the B3LYP method using the 6-311++G(d,p) or 6-311++G(2df,2p) basis sets. The deprotonation enthalpies (DPE) of the CH bond or the proton affinities of the carbanions (PA(C-) are calculated as well. All the systems with the exception of the CH4...CHCl2(-) one are characterized by a double minimum potential. In some of the complexes, the (CH(b)...C)- hydrogen bond is linear. In other systems, such as CH3F...CH2F- and CH3F...CHF2(-), there is a large departure from linearity, the systems being stabilized by electrostatic interactions between the nonbonded H of the neutral molecule and the F atom of the carbanion. In the transition state, the (CH(b)...C)- bond is linear, and there is a large contraction of the intermolecular C...C distance. The binding energies vary within a large range, from -1.4 to -11.1 kcal mol(-1) for the stable complexes and -8.6 to -44.1 kcal mol(-1) for the metastable complexes. The energy barriers to proton transfer are between 5 and 20 kcal mol(-1) for the heteroconjugate systems and between 3.8 and 8.3 kcal mol(-1) for the homoconjugate systems. The binding energies of the linear complexes depend exponentially on 1.5DPE - PA(C-), showing that the proton donor is more important than the proton acceptor in determining hydrogen bond strength. The NBO analysis indicates an important electronic reorganization in the two partners. The elongations of the CH bond resulting from the interaction with the carbanion depend on the occupation of the sigma*(CH(b)) antibonding orbitals and on the hybridization of the C bonded to H(b). The frequency shifts of the nu(CH)(A1) stretching vibration range between 15 and 1150 cm(-1). They are linearly correlated to the elongation of the CH(b) bond.     

(Trifluoromethyl)germanes. Preparation and properties of (CF3)2GeHX (X = H,D, F,Cl, Br,I, CH3) and CF3GeHnX3-n (X = H,D, CF2H,CH3)

The hydrogenation of (CF₃)_nGeX_4-n (X = halogen, n = 1–3) with NaBH₄ in an acidic medium has been investigated. Deuteration with NaBD₄ and D₃PO₄ gave the partially deuterated species CF₃GeH_nD_3-n and (CF₃)₂GeH_nD_2-n in reasonable isotopic purity. The (CF₃)₂GeHBr was isolated and converted into the halides (CF₃)₂GeHX (X = F, Cl, I) by treatment with AgX or HX. Insertion of CF₂ into a GeH bond has been observed, and (CF₃)(CF₂H)GeH₂ has been characterized. Direct alkylation of GeH bonds was brought about by reaction with a mixture of RI and R′₂Zn (R, R′= CH₃, C₂H₅), and the methyl(trif]uoromethyl)germanes CF₃GeH₂(CH₃), CF₃GeH(CH₃)₂ and (CF₃)₂GeH(CH₃) were isolated. For R = CD₃, R′ = CH₃ the product distribution can be accounted in terms of two competing mechanisms.     

Halogen-hydride interaction between Z-X (Z = CN, NC; X = F, Cl, Br) and H-Mg-Y (Y = H, F, Cl, Br, CH3)

Halogen-hydride interactions between Z-X (Z = CN, NC and X = F, Cl, Br) as halogen donor and H-Mg-Y (Y = H, F, Cl, Br, CH(3)) as electron donor have been investigated through the use of Becke three-parameter hybrid exchange with Lee-Yang-Parr correlation (B3LYP), second-order M?ller-Plesset perturbation theory (MP2), and coupled-cluster single and double excitation (with triple excitations) [CCSD(T)] approaches. Geometry changes during the halogen-hydride interaction are accompanied by a mutual polarization of both partners with some charge transfer occurring from the electron donor subunit. Interaction energies computed at MP2 level vary from -1.23 to -2.99 kJ/mol for Z-F···H-Mg-Y complexes, indicating that the fluorine interactions are relatively very weak but not negligible. Instead, for chlorine- and bromine-containing complexes the interaction energies span from -5.78 to a maximum of -26.42 kJ/mol, which intimate that the interactions are comparable to conventional hydrogen bonding. Moreover, the calculated interaction energy was found to increase in magnitude with increasing positive electrostatic potential on the extension of Z-X bond. Analysis of geometric, vibrational frequency shift and the interaction energies indicates that, depending on the halogen, CN-X···H interactions are about 1.3-2.0 times stronger than NC-X···H interactions in which the halogen bonds to carbon. We also identified a clear dependence of the halogen-hydride bond strength on the electron-donating or -withdrawing effect of the substituent in the H-Mg-Y subunits. Furthermore, the electronic and structural properties of the resulting complexes have been unveiled by means of the atoms in molecules (AIM) and natural bond orbital (NBO) analyses. Finally, several correlative relationships between interaction energies and various properties such as binding distance, frequency shift, molecular electrostatic potential, and intermolecular density at bond critical point have been checked for all studied systems.     

Formation and characterization of the uranium methylidene complexes CH2 = UHX (X = F, Cl, and Br)

The reactions between uranium atoms and CH3X (X = F, Cl, and Br) molecules are investigated in a solid argon matrix. The major products formed on ultraviolet irradiation are the CH2=UHX methylidene complexes. DFT calculations predict these triplet ground-state structures to be stable and to have significant agostic interactions. Parallels between the uranium and analogous thorium methylidene complexes are discussed.     

Structures and electron attachment properties of halomethanes (CX(n)Y(m), X=H, F; Y=Cl, Br, I; n=0,4; m=4-n)

Theoretical studies of structures of neutral molecules and their anions as well as dissociative electron attachment properties are presented for the halomethanes of general formula CX(n) Y(m); X=H, F; Y=Cl, Br, I; n=0,4; m=4-n. The dissociative electron attachment seems to be the primary process resulting in toxicity of these species. The halomethane anions containing hydrogens are formed as radical-anion adducts. When H is replaced by F, these species become true sigma* radicals. The electron affinities are computed using a variety of computational techniques including the four-order M?ller-Plesset (MP4) technique that included 250 basis functions. It is challenging to compare the computed results with experiment due to dearth of experimental data and uncertainties in the existing experimental data. Thus in certain cases larger differences are found between the computed and experimental values.     

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     

NMR study (1H, 13C, 31P) of the (C2H5)3-n. PXn compounds (X = Cl,Br, I; n = 0, 1, 2, 3)

The ¹H, ¹³C and ³¹P NMR data are reported for the (C₂H₅)_3-nPX_n compounds (X = Cl, Br, I; n = 0, 1, 2, 3). The chemical shifts are interpreted in terms of inductive and through-space effects of the X substituents together with a rehybridization of the phosphorous atom. The results of the coupling constants are in good agreement with the chemical shifts.     

An MP2 study on pre-reactive complexes (CH_2)_2O … XY (X,Y = H,F,Cl,Br,I)

The structures, energies, atomic chaiges and IR spectra of complexes (CH2)2O…XY (X, Y = H, F, Cl, Br, and I) have been examined by means of ab initio molecular orbital theory at the second-order level of Moller-Plesset perturbation correction. It is found that the hydrogen bond O…H-X is non-linear. The attraction between X and the H atoms in oxirane ring causes O…H-X bond bending. The hydrogen bond slighdy weakens the bond strength of C-O, and leads the bending and stretching mode of IR to shift to the red. The calculation results show that there is no evidence of a significant extent of proton transfer to give (CH2)2OH …X- in the isolated complexes.     

Theoretical investigation of the weakly dihydrogen bonded complexes FArCCH...HBeX (X = H, F, Cl, Br)

An ab initio computational study of the properties of four linear dihydrogen-bonded complexes formed between the first compound with an Ar-C chemical bond (FArCCH) and HBeX (X = H, F, Cl, and Br) molecules was undertaken at the MP2/6-311++G(2d,2p) level of theory. The calculated complexation energy at MP2 and G2(MP2) levels decreases in the order HBeH...HCCArF > BrBeH...HCCArF > ClBeH...HCCArF > FBeH...HCCArF. The intermolecular stretching frequency, and shifts within the monomers, are compared with the energetic strength of complexation.     

HCHO+X(X=F、Cl、Br)的反应机理

采用CCSD/6-311++G(d,p)//B3LYP/6-311++G(d,p)方法研究了HCHO与卤素原子X(X=F、Cl、Br)的反应机理. 计算结果表明, 卤素原子X(X=F、Cl、Br)主要通过直接提取HCHO中的H原子生成HCO+HX(X=F、Cl、Br). 另外还可以生成稳定的中间体, 中间体再通过卤原子夺氢和氢原子直接解离两个反应通道分别生成HCO+HX(X=F、Cl、Br)和H+XCHO(X=F、Cl、Br). 其中卤原子夺氢通道为主反应通道, HCO和HX(X=F、Cl、Br)为主要的反应产物; 且三个反应的活化能均较低, 说明此类反应很容易进行, 计算结果与实验结果符合很好. 电子密度拓扑分析显示, 在HCHO+X反应通道(b)中出现了T型结构过渡态, 结构过渡态(STS)位于能量过渡态(ETS)之后. 并且按F、Cl、Br的顺序, 结构过渡态出现得越来越晚.     

Systematic DFT study of gas phase and solvated uranyl and neptunyl complexes [AnO2X4]n (An = U, Np; X = F, Cl, OH, n = -2; X = H2O, n = +2)

The six-valent uranyl and neptunyl complexes [An(VI)O2X4]n (An = U, Np; X = F, Cl, OH, n = -2; X = H2O, n = +2) have been studied within the framework of density functional theory. The relative stabilities of the cis and trans isomers, structural properties, charge distribution, and ligand binding energies have been determined using the modified Perdew-Burke-Ernzerhof functional at the all-electron scalar relativistic level. Uranyl and neptunyl complexes with different ligands have been compared in a systematic fashion, demonstrating close similarity of these actinides in oxidation state VI. In addition, the effect of an aqueous solution has been taken into account with the polarizable continuum model COSMO. Computed averaged ligand binding energies permit one to rationalize the observed different stabilities of the title species in aqueous media.     

Theoretical study of structure, stability and infrared spectra of CH3X-SO3 (X = F, Cl, Br) complexes

Ab initio computational study of the electronic structure and infrared spectra of donor-acceptor complexes formed between SO3 and CH3X (X = F, Cl, Br) molecules was carried out at the MP2(full)/6-31G(d) level of theory. The calculated complexation energy at G2MP2 level shows that stability of complexes decrease, as CH3Cl-SO3 > CH3Br-SO3 > CH3F-SO3. The NBO partitioning scheme show that the lengthening of the C-F, C-Cl, and C-Br bond lengths, upon complexation, is due to an decreasing "s" character in these bonds.     

Theoretical investigation of the relative stabilities of XSSX and X2SS isomers (X = F,Cl, H,and CH3)

The structures and relative stabilities of a series of disulfide (XSSX) and thiosulfoxide (X₂SS) isomers have been studied for X = F, Cl, CH₃, and H, using various levels of conventional ab initio and density functional theory (DFT). The XSSX isomers are more stable than the X₂SS isomers for all substituents. The energy gap ΔE(X) between the two isomers increases (i.e., XSSX becomes more stable with respect to X₂SS), and the S? S bond contracts in the series for X = F, Cl, CH₃, H. The results are interpreted by means of natural population analysis (NPA) (e.g., the interaction between the disulfide moiety S and the two substituents X·). The bonding in the hypervalent X₂SS species is similar to the bonding in the nonhypervalent XSSX and does not involve a special role for sulfur-3d orbitals. These orbitals acquire only minimal populations and are not to be conceived as valence orbitals. The DFT and conventional ab initio results, Xα/DZP and MP2/6-31G** optimized structures and isomerization energies (at the highest levels of both methods), agree well. © 1995 by John Wiley & Sons, Inc.     

Redox energetics of hypercloso boron hydrides B(n)H(n) (n = 6-13) and B12X12 (X = F, Cl, OH, and CH3)

The reduction potentials (E°(Red) versus SHE) of hypercloso boron hydrides B(n)H(n) (n = 6-13) and B(12)X(12) (X = F, Cl, OH, and CH(3)) in water have been computed using the Conductor-like Polarizable Continuum Model (CPCM) and the Solvation Model Density (SMD) method for solvation modeling. The B3LYP/aug-cc-pvtz and M06-2X/aug-cc-pvtz as well as G4 level of theory were applied to determine the free energies of the first and second electron attachment (ΔG(E.A.)) to boron clusters. The solvation free energies (ΔG(solv)) greatly depend on the choice of the cavity set (UAKS, Pauling, or SMD) while the dependence on the choice of exchange/correlation functional is modest. The SMD cavity set gives the largest ΔΔG(solv) for B(n)H(n)(0/-) and B(n)H(n)(-/2-) while the UAKS cavity set gives the smallest ΔΔG(solv) value. The E°(Red) of B(n)H(n)(-/2-) (n = 6-12) with the G4/M06-2X(Pauling) (energy/solvation(cavity)) combination agrees within 0.2 V of experimental values. The experimental oxidative stability (E(1/2)) of B(n)X(n)(2-) (X = F, Cl, OH, and CH(3)) is usually located between the values predicted using the B3LYP and M06-2X functionals. The disproportionation free energies (ΔG(dpro)) of 2B(n)H(n)(-) → B(n)H(n) + B(n)H(n)(2-) reveal that the stabilities of B(n)H(n)(-) (n = 6-13) to disproportionation decrease in the order B(8)H(8)(-) > B(9)H(9)(-) > B(11)H(11)(-) > B(10)H(10)(-). The spin densities in B(12)X(12)(-) (X = F, Cl, OH, and CH(3)) tend to delocalize on the boron atoms rather than on the exterior functional groups. The partitioning of ΔG(solv)(B(n)H(n)(2-)) over spheres allows a rationalization of the nonlinear correlation between ΔG(E.A.) and E°(Red) for B(6)H(6)(-/2-), B(11)H(11)(-/2-), and B(13)H(13)(-/2-).     

Atmospheric reactions Cl+CH3-(CH2)n-OH (n=0-4): a kinetic and theoretical study

The reactions of Cl with a series of linear alcohols: methanol (k1), ethanol (k2), 1-propanol (k3), 1-butanol (k4), and 1-pentanol (k5) were investigated as a function of temperature in the range of 264-382 K by laser photolysis-resonance fluorescence. The obtained kinetic data were used to derive the following Arrhenius expressions: k1=(3.55+/-0.22)x10(-10) exp[-(559+/-40)T], k2=(5.25+/-0.52)x10(-11) exp[(190+/-68)T], k3=(2.63+/-0.21)x10(-11) exp[(525+/-51)T], k4=(3.12+/-0.31)x10(-11) exp[(548+/-65)T], and k5=(3.97+/-0.48)x10(-11) exp[(533+/-77)T] (in units of cm(3) molecule(-1) s(-1)). To our knowledge, these are the first absolute kinetic data reported for 1-butanol and 1-pentanol and also the first kinetic study as a function of temperature for these two compounds. Results, mechanism, and tropospheric implications are discussed and compared with the reported reactivity with OH radicals. Moreover, a theoretical insight into the mechanisms of these reactions has also been pursued through ab initio M?ller-Plesset second-order perturbation treatment calculations with 6-311G** basis sets. Optimized geometries and vibrational frequencies have been obtained for transition states and molecular complexes appearing along the different reaction pathways. Furthermore, molecular energies have been calculated at quadratic configuration interaction with single, double, and triple excitations level in order to get an estimation of the activation energies.     

Reaction-path dynamics and theoretical rate constants for the CH(n)F(4-n) + O3 --> HOOO + CH(n-1)F(4-n) (n = 2,3) reactions

We present a theoretical study of the hydrogen abstraction reactions from CH(3)F and CH(2)F(2) by an ozone molecule. The geometries and harmonic vibrational frequencies of all stationary points are calculated at the MPW1K, BHandHLYP, and MPWB1K levels of theory. The energies of all of the stationary points were refined by using both higher-level (denoted as HL) energy calculations and QCISD(T)/6-311++G(2df,2pd) calculations based on the optimized geometries at the MPW1K/6-31+G(d,p) level of theory. The minimum energy paths (MEPs) were obtained by the MPW1K/6-31+G(d,p) level of theory. Energetic information of the points along the MEPs is further refined by the HL method. The rate constants were evaluated on the basis of the MEPs from the HL level of theory in the temperature range 200-2500 K by using the conventional transition-state theory (TST), the canonical variational transition-state theory (CVT), the microcanonical variational transition-state theory (microVT), the CVT coupled with the small-curvature tunneling (SCT) correction (CVT/SCT), and the microVT coupled with the Eckart tunneling correction (microVT/Eckart) based on the ab initio calculations. A general agreement was found among the TST, CVT, and microVT theories. The fitted three-parameter Arrhenius expressions of the calculated forward CVT/SCT and microVT/Eckart rate constants of the ozonolysis of fluoromethane are k(CVT/SCT)(T) = 2.76 x 10(-34)T(5.81)e((-13975/)(T)) and k(microVT/Eckart)(T) = 1.15 x 10(-34)T(5.97)e((-14530.7/)(T)), respectively. The fitted three-parameter Arrhenius expressions of the calculated forward CVT/SCT and microVT/Eckart rate constants of the ozonolysis of difluoromethane are k(CVT/SCT)(T) = 2.29 x 10(-36)T(6.42)e((-15451.6/)(T)) and k(microVT/Eckart)(T) = 1.31 x 10(-36)T(6.45)e((-15465.8/)(T)), respectively.     

Darstellung und spektroskopische Charakterisierung der Fluorphosphonium-Salze X2FPSCH3+MF6− (X = Br,Cl; M = As,Sb) und XF2PSCH3+SbF6− (X = Br,Cl, F)

Preparation and Spectroscopic Characterization of the Fluorophosphonium Salts X₂FPSCH₃⁺MF₆^? (X = Br, Cl; M = As, Sb) and XF₂PSCH₃⁺SbF₆^? (X = Br, Cl, F) The preparation of the fluorophosphonium salts X₂FPSCH₃⁺MF₆^? (X = Br, Cl; M = As, Sb) and XF₂PSCH₃⁺SbF₆^? (X = Br, Cl, F) by methylation of the corresponding thiophosphorylhalides in the system CH₃F/SO₂/MF₅ (M = As, Sb) is reported. The new salts are characterized by their vibrational and NMR spectra.