Dimerization of iminophosphoryl compounds and electrophilicity of the antibonding oribitals of the phosphorus atom

The capacity of compounds containing the iminophosphoryl group for dimerization has been considered in the framework of a previously proposed qualitative model of the dependence of the electrophilicity of antibonding orbitals on the structure of molecules. Dimerization involves the attack of the lone pair of the nitrogen atom on the most electrophilic ^* orbital of another molecule of the iminophosphoryl compound. In contrast to the existing theories, it follows from the present treatment that the replacement of one or two groupings on the phosphorus atom by groupings with stronger electron-donor properties should not have a significant influence on the capacity of a molecule for dimerization.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 536–543, September–October, 1985.     

Dependence of the δ31P chemical shift on the electronic and stereochemical structure of compounds of tricoordinated phosphorus

The trends in the variation of the paramagnetic component p^p of the magnetic screening constant of the ³¹p nucleus with variation in the electronic and stereochemical structure of the compounds of tricoordinated phosphorus are examined on the basis of the concepts of perturbation theory. The dependence of p^p on the bond angle at the phosphorus atom in symmetrically substituted phosphines PM₃, on the electronegativity of the substituents M, and on the resonance integral of interaction in the a bonds of the phosphorus atom was investigated. The nature of the ³¹P chemical shift in the transition from phosphines PM₃ to symmetrical phosphonium salts P⁺M₄, and the role of the unshared electron pair of the phosphorus atom in the screening of its nucleus are examined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 419–426, July–August, 1986.     

Theoretical investigation of nature of δ31P chemical shift in phosphonium salts

A simple quantum-chemical approach is proposed for investigation of the nature of the ³¹P chemical shift in phosphonium salts — an approach based on perturbation theory. The experimentally observed trends in the change in ³¹P in these compounds are explained by the features of their electronic and steric structure (without considering interelectron interactions or the 3d orbitals of phosphorus). An analysis is made of the dependence of the paramagnetic component of the³¹P nuclear magnetic screening constant in phosphonium salts on the electronegativity of the substituents on the P atom, the multiplicity of the bonds to the P atom, and the magnitude of the resonance integral of interaction in the a components of these bonds.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 21, No. 2, pp. 165–175, March–April, 1985.     

Structure of organophosphorus compounds. Part XLII. The molecular structure of the 2,6-di-tert-butyl-4-methylphenyl ester of N-[2,4,6-tri(tert-butyl)-phenyl]phosphenimidous acid

This is the first x-ray diffraction structural analysis of a dicoordinated phosphorus derivative with an N=P–O group, namely, the 2,6-di-tert-butylmethylphenyl ester of N-[2,4,6-tri(tert-butyl)phenyl]phosphenimidous acid (I) using Mo radiation and 6552 reflections to R=0.045. The unit cell parameters of the triclinic crystals are as follows: a=9.297, b=12.004, c=15.031, =107.87, =101.50, =95.50°, V=1542 ų, d _calc =1.1 g/cm³, Z=2, space group P . The bond angle at the dicoordinated phosphorus atom is 110.3° and the PNC angle is 173.7°. The change in the hybridization of the nitrogen atom in I toward sp and the enhancement of the n _N , _P–O * interaction lead to shortening of the P=N and N–C bonds to 1.500 and 1.395 Å and elongation of the P–O bond to 1.658 Å. The steric strain in I leads to nonplanarity of the central group. The CNOP torsion angle is 86.3°, while the NPOC torsion angle is 169.2°.Part XLI, see ref. [1].Institute of Organic Chemistry, Academy of Sciences of the Ukrainian SSR. A. N. Nesmeyanov Institute of Heteroorganic Compounds, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 6, pp. 105–111, November–December, 1989.     

Alkyl radical hyperconjugation in phosphorus compounds

Conclusions The³¹P and¹⁹F chemical shifts in phosphorus compounds of various conformations vary with the number of hydrogen or fluorine atoms attached to the-C atom of the phosphorus atom alkyl or perfluoroalkyl radical. This effect can be explained in terms of alkyl radical hyperconjugation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2435–2439, September, 1976.     

Effect of dissociation on the reactivity and inhibition capacity of p-nitro-phenol towards ortho-positronium in methanol solutions

The effect of dissociation on the reactivity and inhibition capacity of p-nitro-phenol /p-NPH/ towards orthopositronium atom has been investigated by performing positron lifetime measurements in methanol and methanol containing 0.5M NaOH solutions, respectively. In the latter case the solute exists in anionic form /p-NP^–/. It has been found that as a result of dissociation, both the rate constant /k/ and the inhibition coefficient // decrease significantly. Their values are k=/7.5±0.4/×10⁸ s^–1 M^–1 and =6.8±0.2 M^–1 for p-NPH and k_d=/0.6±0.2/×10⁸ s^–1 M^–1 and _d=4.0±0.2 M^–1 for p-NP^–. The possible reasons for these effects are discussed.     

Synthesis and X-ray crystal structure of complexes Cp(CO)2MnP(SR)3 (R = Pri,Ph)

Cp(CO)₂Mn · THF reacts in THF with thiosters of phosphorus acid, P(SR)₃, to give new complexes Cp(CO)₂MnP(SR)₃ in which the manganese atom is coordinated to the phosphorus atom. The X-ray crystal structure of compounds with R = Prⁱ and Ph was established. The metal atom has a coordination enviroment of the three-legged piano stool type. The bond angles OC-Mn-CO and OC-Mn-P are 90.6–95.9(4)°. Bond distances are: Mn-P 2.188(2) and 2.171(2) E, P-S 2.097(3)-2.137(3) E.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1116–1119, June, 1994.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No.93-03-5830).     

Reactions ofβ-chloroethyl derivatives of tricoordinated phosphorus acids with 1-nitro-1-propene

Conclusions The reactions of the-chloroethyl derivatives of trivalent phosphorus acids proceed via an ionic intermediate, which, depending on the experimental conditions, is stabilized in the direction of ring closure to give an adduct with a pentacovalent phosphorus atom and the formation of the corresponding unsaturated and (-methyl--nitroethyl)phosphoryl compounds. The liberated-chloroethyl nitrite functions as an oxidizing agent of the starting-chloroethyl derivatives of trivalent phosphorus acids.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1398–1401, June, 1978.The authors thank É. I. Gol'dfarb for taking the³¹P–{¹H} NMDR spectra.     

Interaction of Chloride Anion and Chlorine Atom with Indium and Gallium Surfaces: A Quantum-chemical Study

The adsorption of the chloride ion and chlorine atom on clusters simulating the surface of the (111) and (001) faces of the crystal lattice of indium and liquid gallium are calculated using the Hartree–Fock–Roothaan and density functional (B3LYP) quantum-chemical methods. The energy of adsorption of chloride ions from a gas phase at these faces increases in the following series: bridgehollow < on-top positions and equals to 179 kJ mol^–1 for In(111) and 183 kJ mol^–1 for gallium in the on-top position. Both metals exhibit similarity in the formation of bonds between their surface atoms and the adsorbate. The adsorbate charge does not depend on the adsorbed form (chloride ion or chlorine atom) and equals 0.5e. Parameter of a virial adsorption isotherm is estimated with allowance for coulombic interactions near the metal/electrolyte interface.     

Chromatographic Determination of Silicon and Phosphorus as Molybdic Heteropoly Acids with Preconcentration

The chromatographic behavior of molybdic heteropoly acids of silicon and phosphorus as ion pairs with tetrabutylammonium bromide was studied by ion-pair high-performance liquid chromatography on the C₁₈reversed phase (UV detection at 310 nm). Heteropoly acids were preconcentrated as ion pairs with tetrabutylammonium bromide to increase the sensitivity of the determination. Optimal conditions were selected for the chromatographic determination of silicon and phosphorus in water in the presence of each other. Detection limits for silicon and phosphorus are (1.1 × 0.3) × 10^–3and (6.7 × 1.2) × 10^–3g/mL, respectively. Calibration plots are linear in the concentration ranges 0.01–0.1 g/mL (silicon) and 0.02–0.15 g/mL (phosphorus). The procedure was used for the analysis of distilled water.     

Alpha-recoil atoms of plutonium in the environment

The -recoil effect of²³⁹Pu has been observed in environmental samples and theN ₅ ^P /N₅ ratio in these samples has been calculated. This ratio in atmospheric samples is in the range between 10^–5 and 10^–4 (atom/atom). For other contemporary terrestrial samples it is in the range between 10^–7 and 10^–6 (atom/atom), while that of uranium mineral is about 10^–10 (atom/atom). The results further explain the radioactive fallout contamination of our environment by uranium and plutonium isotopes.     

Nitrogen-containing organosilicon compounds. 150. Synthesis and chromatographic and 1H, 13C, 15N,and 29Si NMR spectroscopic investigation of substituted (piperidinoalkyl)silanes

Substituted (piperidinoalkyl)silanes were synthesized and investigated by means of multinuclear NMR spectroscopy and GLC. The data obtained indicate an additional N-Si interaction in -aminomethylsilanes that depends substantially on the properties of the substituents attached to the silicon atom. The effect of the R¹R²R³Si substituent on the capacity of the nitrogen atom for intermolecular interactions is not restricted to steric effects but also has electronic character.See [1] for communication 149.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1644–1652, December, 1991.     

1 H and 13 C NMR spectra and structure of 2-trichloromethyl-4-methylene-1,3-dioxolanes

The ¹H and ¹³C NMR spectra of a number of 5-substituted 2-trichloromethyl-4-methylene-1,3-dioxolanes were studied. It was observed that the exocyclic double bond is in effective conjugation with the 3–0 ring atom. The configuration of the substituents was established, and a conformational model of these heterocycles of the envelope type with the 1–0 atom deviating from the plane in which the remaining ring atoms are situated is proposed. The applicability of the ¹³C NMR spectra for the determination of the configuration of the compounds is demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1176–1180, September, 1976.     

Theoretical studies of the benzene oxide—oxepin valence tautomerism

We have calculated the geometry and energy of the valence tautomers benzene oxide and oxepin using the semiempirical AM1 model and the 6–31G and 6–31G^* basis sets utilizing full geometry optimization. In the oxide the folding angle, the angle between the epoxide ring and the adjacent plane containing four carbon atoms, is about 106°. The carbon skeleton is almost planar, the folding angle, the angle between the two four-carbon atom planes being about 175°. In contrast, oxepin is found to have a marked boat-shaped structure with the corresponding and angles about 137° and 159°, respectively. The AM1, 6–31G, and 6–31G^* calculations give –11.4, –10.8, and –2.9 kcal mol^–1 for the energy change that accompanies the valence tautomerism, oxide-oxepin, compared to an experimental value of about +0.3 kcal mol^–1. Single point calculations of the energies at the 6–31 G^* geometry using Møller-Plesset perturbation theory to second order (MP2/6–31 G^*) and third order (MP3/6–31G^*) give E _T =+3.3 and +0.8 kcal mol^–1. The values for the energy change in the transfer of epoxide oxygen from ethylene oxide to benzene using AM1, 6–31G, and 6–31G^* are in good agreement, viz., +31.1, +34.5, and +33.6 kcal mol^–1, respectively. A large positive energy change is to be expected in view of the loss of benzene aromaticity.     

Role of multiple bonds of tetracoordinated phosphorus atom in the magnetic shielding of its nucleus

On the basis of a previously proposed approach to investigation of the nature of the chemical shift ³¹P, it has been shown that the dependence of shielding of the ³¹P nucleus on the multiplicity of one of the bonds (PM) of the phosphorus atom in the molecule is not monotonic over the entire interval of variation of the corresponding parameter _PM. When _PM is smaller than a certain value ₀, which is determined by the difference between interactions of the P atom with the atom in question (M) and other substituents, the dependence of ³¹P nuclear shielding on _PM should be antibatic, and when _PM > ₀ symbatic.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 439–446, July– August, 1989.     

Theoretical Study of Chemical Binding of Noble Gas Atom and Transition Metal Complexes: Ng–NiCO, Ng–NiN2, Ng–CoCO (Ng = He–Xe)

Ab initio multireference and coupled cluster methods (MR-SDCI(+Q), CASPT2, CCSD(T)) and density functional theory methods (B3LYP, MPWPW91) have been applied to examine geometrical structures and vibrational frequencies of noble gas (Ng) – transition metal compounds, Ng–NiCO, Ng–NiN₂, and Ng–CoCO (Ng = He, Ne, Ar, Kr, Xe). It is shown that the respective compounds can have a larger binding energy than a typical van der Waals interaction energy. The binding mechanism is explained by a partial electron transfer from a noble gas atom to the low-lying 4s and 3d vacant orbitals of the transition metal atom. Theoretical calculations show that the binding of noble gas atom results in a large shift of the bending frequency: 361.1cm^–1 (NiCO) to 403.5cm^–1 (Ar–NiCO); 308.5cm^–1 (NiN₂) to 354.8cm^–1 (Ar–NiN₂); 373.0cm^–1 (CoCO) to 422.6cm^–1 (Ar–CoCO). The corresponding experimental frequencies determined in solid argon are 409.1cm^–1 (NiCO), 357.0cm^–1 (NiN₂), and 424.9cm^–1 (CoCO), which are much closer to the corresponding frequency of Ar–NiCO, Ar–NiN₂, and Ar–CoCO, respectively.     

Correlation of the nuclear quadrupole resonance frequencies of Cl35 of dihydrochlorides of certain phosphorus acids with the σφ constants of substituents on the phosphorus atom

Conclusions Two linear relationships exist between the nuclear quadrupole resonance frequencies of Cl³⁵ in dichlorides of certain phosphorus acids and the constants of substituents at the phosphorus atom; one of them is formed by alkyldichlorophosphonates, while the other is given by compounds in which conjugation is possible between the substituent and the d-orbitals of phosphorus-alkyldichlorophosphates, aryl- and vinyldichlorophosphonates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2375–2378, November, 1967.Some of the substances were synthesized by G. P. Kharitonova, whom the authors would like to thank.     

Theoretical Study of Chemical Binding of Noble Gas Atom and Transition Metal Complexes: Ng–NiCO, Ng–NiN2, Ng–CoCO (Ng = He–Xe)

Summary. Ab initio multireference and coupled cluster methods (MR-SDCI(+Q), CASPT2, CCSD(T)) and density functional theory methods (B3LYP, MPWPW91) have been applied to examine geometrical structures and vibrational frequencies of noble gas (Ng) – transition metal compounds, Ng–NiCO, Ng–NiN₂, and Ng–CoCO (Ng = He, Ne, Ar, Kr, Xe). It is shown that the respective compounds can have a larger binding energy than a typical van der Waals interaction energy. The binding mechanism is explained by a partial electron transfer from a noble gas atom to the low-lying 4s and 3d vacant orbitals of the transition metal atom. Theoretical calculations show that the binding of noble gas atom results in a large shift of the bending frequency: 361.1cm^–1 (NiCO) to 403.5cm^–1 (Ar–NiCO); 308.5cm^–1 (NiN₂) to 354.8cm^–1 (Ar–NiN₂); 373.0cm^–1 (CoCO) to 422.6cm^–1 (Ar–CoCO). The corresponding experimental frequencies determined in solid argon are 409.1cm^–1 (NiCO), 357.0cm^–1 (NiN₂), and 424.9cm^–1 (CoCO), which are much closer to the corresponding frequency of Ar–NiCO, Ar–NiN₂, and Ar–CoCO, respectively.     

The Three-Center, Four-Electron Bond in Hexacoordinated AB6-Type Main Group Molecules: An Alternative Model of Bonding without d-Orbital Participation in the Central Atom

The hexacoordinated AB₆-type main group molecules have long been thought to have sp³d² hybridization on the central atom, accounting for their molecular geometry (octahedral). However, the s-p-d hybridization does not explain how an energetically unfavorable np nd excitation in an atom of nonmetallic elements, such as sulfur and phosphorus, can be achieved. In this article, the author has re-examined bonding in SF₆ and PF₆^– (O_h symmetry) and proposed that the linear F—S—F and F—P—F bonds in both species are formed via the overlap of the 3p orbital on the central atom with terminal ligand orbitals, resulting in a three-center, four-electron bond. This alternative model, which does not involve d orbitals in bonding, is supported by a partial charge analysis using Allens electronegativity approach. SF₆ or PF₆^– can be characterized by several ionic resonance structures containing a postulated SF₄²⁺ or PF₄⁺ cation (octet on sulfur or phosphorus). The three-center, four-electron bond model can also be used to study bonding in hexacoordinated AB₅E (e.g., halogen pentafluorides) and AB₄E₂ (e.g., xenon tetrafluoride) explaining well the molecular geometry. The author believes that all the results will be useful in updating chemistry texts.     

Fluorine analysis of standard materials by short-time activation analysis using20F

Phosphorus at trace levels alters the properties of metals and alloys. Its determination was investigated by radiochemical neutron activation analysis. Separation by solvent extraction or by evolution as P⁰ showed to be neither selective nor quantitative in presence of a metallic matrix. Therefore, a new method of separation by reduction to phosphorus hydride followed by liquid scintillation counting was investigated. This method is quantitative in the case of non-radioactive iron doped with radioactive phosphorus. At present, the separation is not quantitative for irradiated iron samples, owing probably to hot atom or radiation effects. A detection limit of 0.002 g is expected.Presented at the MTAA-8 Conference, September 16–20, 1991, Vienna, Austria.