Reactivity of Ph3PNLi towards P and P electrophiles

A study of the reactivity of Ph₃PNLi towards phosphorus electrophiles allowed us to develop a general method to isolate, or cleanly generate in situ, a broad family of polyphosphinimines displaying PN-P bonds. A preliminary application of this methodology is presented here with the synthesis of various Schwesinger-type bases by a simple new procedure employing Ph₃PNLi.     

Low-lying states of cs22+

Using an MC SCF CI method, wavefunctions for the ground state ¹∑⁺_g and the excited states of the symmetries ¹∑⁺_g, ¹Π_g, and ¹Δ_g of the Cs²⁺₂ ionic system are generated. The potential curves for eleven ¹∑⁺_g twelve ¹Π_g, and six ¹Δ_g states are calculated. Results suggest a small charge-transfer cross section for the reaction CS⁺ + Cs⁺ → Cs CS²⁺.     

Reactivity of Cl(2P1/2) atoms towards CH3F

The photochlorination of methyl fluoride has been studied at low pressures. Excited (²P_1/2) chlorine atoms have been found to participate in the reaction. The ratio of the excited and ground state rate constants has been estimated at room temperature.

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. (²P_1/2) . .

     

Reactivity of RCu,BF3 and R2 CuLi,BF3 towards allylic acetals and ethers

Organocopper and cuprate reagents associated with Lewis acids, are highly reactive towards allylic acetals and ethers. Displacements of the alkoxy group occurs by SN₂' attack according to the various parameters of the reaction.     

Reactivity of plasma-treated SiO2 against O2: An EPR study

During plasma treated of SiO₂ (dehydrated at 700°C in high vacuum) electrons become trapped at the surface and in the bulk. The captured electrons from the well known E_í centre, an F-like electron centre with the unpaired electron mainly in an s-type orbital, and CO₂^? which comes from carbon impurities. Adsorption of O₂ (partial pressure 5 × 10^-3 torr ? po₂ ? 10 ^?1 torr) gives O₂^? species that depend on the adsorption temperature, characterized by the following g-values: g₁ = 2.069, g₂ = 2.000m T_ads = 300 K; g₁ = 2.039, g₂ = 2.007, g₃ = 2.002, T_ads = 77 K.     

Reactivity of coordinated O2? towards. One-electron oxidants

Ion-radical complexes Ti(IV) (O ₂ ^– ) are unreactive towards most oxidants except Ce(IV) and Cr₂O ₇ ^2– . The one-electron redox potential for the O_{2 coord.}/O _{2 coord.} ^– couple lies between 1 and 1.6 V.

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- O ₂ ^– Ti(IV) , Ce(IV) Cr₂ O ₇ ^2– . - O_{2 .}/O ₂ ^– . 1 1,6 .

     

Reactivity of electronically excited Br(2P1/2) atoms towards CH3F

The rate constants for Br(²P_1/2) and Br(²P_3/2) atoms in the reaction Br+CH₃FHBr+CH₂F in photobromination of CH₃F have been determined. Their ratio is 10^{–(2.6±0.5)} exp(10100±1000/RT) in the temperature range of 60–200 °C.

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Br(²P_1/2) Br(²P_3/2) Br+CH₃FHBr+CH₂F CH₃F. 60–200 °C 10^{–(2,6±0,5)} exp (10100±1000/RT).

     

Kinetics of the reaction of NH2 with NO2

The absolute rate constant of the reaction of NH₂ with NO₂ has been measured using a flash-photolysis laser resonance-fluorescence technique. The value obtained at room temperature is k₁ = 2.3 (± 0.2) × 10^?11 cm³ molecule ^?1 s^?1. A negative temperature coefficient has been found between 298 and 505 K for this reaction, k₁ = 3.8 × 10^?8 × T^?1.30 cm³ molecule^?1 s^?1. It is thought that this is the major reaction of NH₂ in the troposphere.     

The reaction of (SO2)2 and (CO2)2 with Ba

The reactions of (CO₂)₂ and (SO₂)₂ with Ba have been investigated using a crossed beam arrangement and the laser-induced fluorescence technique. Internal energy in the BaO product was probed in order to study differences between monomeric and dimeric reactions. The reaction cross section for the dimers of CO₂ was found to be between four and eightfold larger than that of the monomers. This can be explained by the change in the reaction mechanism due to the positive electron affinity of the dimers versus the negative electron affinity of the monomers. The product BaO from the dimeric reactions is much colder rotationally than in the monomeric case. This phenomenon can be explained based on the kinematics.     

Reactivity of RCu,BF3 and R2CuLi,BF3 towards the ether linkage. Epoxides,acetals and orthoformates

The association of BF₃ to organocopper and cuprate reagents increases dramatically their reactivity towards epoxides. The same reagents cleave acetals to afford the product of substitution of one alkoxy group, whereas orthoformates lead to acetals under conditions where no further attack occurs.     

Reactivity studies of trans-[PtClMe(SMe2)2] towards anionic and neutral ligand substitution processes

Reaction of trans-[PtClMe(SMe₂)₂] with the mono anionic ligands azide, bromide, cyanide, iodide and thiocyanate result in substitution of the chloro ligand as the first step. In contrast the neutral ligands pyridine, 4-Me-pyridine and thiourea substitute a SMe₂ ligand in the first step as confirmed by ¹H NMR spectroscopy and the kinetic data. Detailed kinetic studies were performed in methanol as solvent by use of conventional stopped-flow spectrophotometry. All processes follow the usual two-term rate law for square-planar substitutions, k_obs = k₁ + k₂[Y] (where k₁ = k_MeOH[MeOH]), with k₁ = 0.088 ± 0.004 s⁻¹ and k₂ = 1.18 ± 0.13, 3.8 ± 0.3, 17.8 ± 1.3, 34.9 ± 1.4, 75.3 ± 1.1 mol⁻¹ dm³ s⁻¹ for Y⁻ = N₃, Br, CN, I and SCN respectively at 298 K. The reactions with the neutral ligands proceed without an appreciable intercept with k₂ = 5.1 ± 0.3, 15.3 ± 1.8 and 195 ± 3 mol⁻¹ dm³ s⁻¹ for Y = pyridine, 4-Me-pyridine and thiourea, respectively, at 298 K. Activation parameters for MeOH, , Br⁻, CN⁻, I⁻, SCN⁻, and Tu are ΔH^≠ = 47.1 ± 1.6, 49.8 ± 0.6, 39 ± 3, 32 ± 8, 39 ± 5, 34 ± 4 and 31 ± 3 kJ mol⁻¹ and ΔS^≠ = −107 ± 5, −77 ± 2, −104 ± 9,−113 ± 28, −85 ± 18, −94 ± 14 and −97 ± 10 J K⁻¹ mol⁻¹, respectively. Recalculation of k₁ to second-order units gives the following sequence of nucleophilicity: (1:13:42:57:170:200:390:840:2170) at 298 K. Variation of the leaving group in the reaction between trans-[PtXMe(SMe₂)₂] and SCN⁻ follows the same rate law as stated above with k₂ = 75.3 ± 1.1, 236 ± 4 and 442 ± 5 mol⁻¹ dm³ s⁻¹ for X⁻ = Cl, I and N₃, respectively, at 298 K. The corresponding activation parameters were determined as ΔH^≠ = 34 ± 4, 32 ± 2 and 39.3 ± 1.7 kJ mol⁻¹ and ΔS^≠ = −94 ± 14, −86 ± 8 and −68 ± 6 J K⁻¹ mol⁻¹. All the kinetic measurements indicate the usual associate mode of activation for square planar substitution reactions as supported by large negative entropies of activation, a significant dependence of the reaction rate on different entering nucleophiles and a linear free energy relationship.     

A theoretical study of the reaction of SiH2 with C2H2 and C2D2

Potential energy surfaces of the reaction of SiH₂ and C₂H₂ (and C₂D₂) have been calculated by means of ab initio molecular orbital theory at the QCISD/6-311G++(2df, 2p)//MP2/6-31G(d, p) level with corrections for the triple excitations to the QCISD energies. The barrier heights for the two reaction channels of the adduct, thus calculated, were further utilized for the dynamical calculation of the rate constants in the framework of quantum statistical Rice-Ramsperger-Kassel theory. Contributions of the rate constants of the various pathways to the total rate constant (K_T) for the disappearance of the reactants are critically examined and compared with experiment. The pressure dependence of K_T(C₂H₂) is primarily due to the formation of silirene. K_T(C₂D₂) is consistently higher than K_T(C₂H₂). The standard heat of formation of silirene is predicted to be 72.1 ± 3 kcal/mol. Rearrangement of silirene to vinylsilylene requires an activation energy smaller than that to silylacetylene.     

TEA CO2 laser-induced reaction of CH3NO2 with CF2HCl: A mechanistic study

Dissociation of nitromethane has been observed when a mixture of CF₂HCl and CH₃NO₂ is irradiated using pulsed TEA CO₂ laser at 9R (24) line (1081 cm^-1), which is strongly absorbed by CF₂HCl but not by CH₃NO₂. Under low laser fluence conditions, only nitromethane dissociates, whereas at high fluence CF₂HCl also undergoes dissociation, showing that dissociation occurs via the vibrational energy transfer processes from the TEA CO₂ laser-excited CF₂HCl to CH₃NO₂. Time-resolved infrared fluorescence from vibrationally excited CF₂HCl and CH₃NO₂ molecules as well as UV absorption of CF₂ radicals are carried out to elucidate the dynamics of excitation/dissociation and the chemical reactions of the dissociation products.     

The fast reaction of CH2OH with O2

The rate coefficient of the reaction CH₂ + O₂OH → HO₂ + CH₂O, has been measured at 300 K by the LMR flow-tube method, and found to have the unexpectedly large value k = (2_?1⁺²) × 10^?12 cm³ molecule^?1 s^?1. This reaction, preceded by isomerization, may be an important route for the oxidation of CH₃O in the upper atmosphere.     

A kinetics study of the reaction of SO2 with CH3O2

The reaction ot CH₃O₂ with SO₂ has been studied using the flash photolysis/ultraviolet absorption technique. In contrast to previous measurements, no reaction could be detected over the temperature range 298–423 K. An upper limit of 5 × 10^?17 cm³ molecule^?1 s^?1 has been determined for the reaction rate constant.     

Reactivity of Z- and E-isomers of 2-benzamido-3-phenylacrylohydrazide towards some carbon electrophiles. A comparative study

Z- and E-isomers of 2-benzamido-3-phenylacrylohydrazide 2a, 2b have different relative reactivities towards some carbon electrophiles had been discussed.The Z-isomer underwent cyclization to give imidazole derivative 3 and triazine derivative 4, whereas the latter E-isomer does not undergo such cyclization. The reaction of 2a and/or 2b with 1,2-dibenzylidene hydrazine at different reaction conditions afforded the Schiff bases 6, 8 and the triazolidine derivative 9. Reactions of 2a, 2b with formic acid and phthalic anhydride gave the different cyclization products 10–14, respectively. The structures of all the new synthesized compounds were established from their IR, ¹H-NMR and mass spectra as well as elemental analyses.     

Rates of reaction of NH2 with N,NO AND NO2

The decay of NH₂ radicals, from 193 nm photolysis of NH₃, was monitored by 597.7 nm laser-induced fluorescence. Room-temperature rate constants of (1.21 ± 0.14) × 10^?10, (1.81 ± 0.12) × 10^?11, and (2.11 ± 0.18) × 10^?11 cm³ molecule^?1 s^?1 were obtained for the reactions of NH₂ with N, NO and NO₂, respectively. The production of NH in the reaction of NH₂ with N was observed by laser-induced fluorescence at 336.1 nm.     

Reactivity of a functionalized trisamido ligand with Zr(NMe2)4 and GaMe3

NMR study of the reactivity of multifunctional ligand cis,cis-C₆H₉(NHCH₂C₆H₄-o-PPh₂)₃ (1) with GaMe₃ and Zr(NMe₂)₄ was carried out, yielding [cis,cis-(κ^N-NHCH₂C₆H₄-o-PPh₂)(κ^N-NCH₂C₆H₄-o-PPh₂)₂C₆H₉]GaMe (2) and [cis,cis-(NCH₂C₆H₄-o-PPh₂)₃C₆H₉]Ga₂Me₃ (3), and [cis,cis-(NCH₂C₆H₄-o-PPh₂)₃C₆H₉]Zr(NMe₂) (4), respectively. The spectral properties of 2 and 3 are very similar to that observed for the equivalent aluminum species already reported, but form at a much slower rate which allows for the observation of a GaMe₃⋅1 adduct. Species 4 undergoes coordination/displacement of one of the phosphine arms, which was observed using both NMR spectroscopy and DFT analyses.