Nonempirical quantum chemical calculation for nitramide,its chloro- and methyl-substituted derivatives. I. Structure of equilibrium forms

We have carried out quantum chemical calculations for a series of N-nitramines (H₂NNO₂, MeNHNO₂, CINHNO₂, MeNClNO₂, Me₂NNO₂) using the GAUSSIAN-90 program by the restricted Hartree—Fock method, taking into account electron correlation according to Møller—Plesset second-order perturbation theory in a standard 6–31G^* basis. In this paper, we present the geometric parameters of the equilibrium forms of the molecules obtained as a result of full optimization. The calculation allowed us to establish that with an increase in electronegativity of the substituents on the amine nitrogen atom, we observe coordinated lengthening of the NN bond, shortening of the N=O bond, and increase in the pyramidal character of the configuration of the bonds of the amine nitrogen atoms. We observed a close to linear relationship between the length of the NN bond and the magnitude of the angle of deviation of this bond from the plane of the ONO atoms. The greatest difference in NN bond lengths (0.06 Å) occurs between the Me₂NNO₂ and ClNHNO₂ molecules.Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 4–11, January–February, 1993.     

Molecular structures of acetylene derivatives of tin: Part II. Gas phase electron diffraction study ofbis(trimethylstannyl)acetylene,Me3SnCCSnMe3

A gas phase electron diffraction study of bis(trimethylstannyl)acetylene is reported. The r_a structure refines to the following parameters (bond lengths in nm, valence angles in degrees):

The numbers in parentheses are three times the standard deviation values.The difference between the

bond lengths in the bis(trimethyl-stannyl) acetylene molecule is less significant than with trimethylstannylacetylene. The observed departure from linearity in the Sn-CC-Sn fragment is seemingly due to the shrinkage effect.     

Ab initio investigation of tautomeric stability,molecular structure,and internal rotation of methylphosphonic dicyanide,methoxydicyanophosphine, and their isocyano analogs

The equilibrium geometric parameters and structures of the transition states of internal rotation for MeP(O)(CN)₂, McOP(CN)₂, and their isocyano analogs, MeP(O)(NC)₂ and MeOP(NC)₂, have been calculated by theab initio SCF method and with inclusion of electron correlation effects according to the second-order Muuller-Plesset perturbation theory (MP2). At both levels the 6-31G* basis set has been used. The estimation of relative stability of these tautomeric forms depends largely on the calculation level. The total energies of the cyanides calculated by the MP2 method are 25–30 kcal mol^–1 lower than those of the corresponding isocyanides. The oxo-tautomeric forms containing four-coordinate phosphorus are 15–25 kcal mol^–1 more stable than the three-coordinate phosphorus aci-derivatives. The internal rotation potential curves of the aci-forms are characterized by a deep minimum for thetrans-arrangement of the methoxy group and phosphorus lone electron pair. Two additional less clearly pronounced minima are located symmetrically on both sides of the weak maximum, which corresponds to thecis-arrangement. The equilibrium oxo-form structures have a staggered configuration of the methyl group with respect to the phosphorus atom bonds.Translated from izvestiyaAkademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1104–1115, May, 1996.     

Hexamethylenetetramine (urotropine) C6H12N2: Interpreting the vibrational spectra of -d0 and -d12 isotopomers by scaling the quantum-chemical force field

The equilibrium structure and quadratic and cubic force fields of the urotropine molecule are calculated at the MP2 (full)/cc-pVTZ level. Pulay scaling of the quadratic force field allows unambiguous interpretation of the vibrational spectra of -d₀ and -d₁₂ urotropines. A reliable matrix for the quadratic force constants of urotropine is obtained which may be used to determine the parameters of the equilibrium structure of the urotropine molecule by means of gas-phase electron diffraction.     

Multicentered self-immobilized ethylene polymerization catalysts based on functionalized titanium halide salicylaldiminate complexes for the synthesis of ultra-high-molecular-weight polyethylene

Specific features of ethylene polymerization using a new group of catalytic systems based on ten methylalumoxane-activated titanium halide salicylaldiminato complexes functionalized with ??-vinylalkoxy groups and containing tert-butyl substituents in the phenoxide moiety were studied. The catalytic activity of the new group of activated complexes is strongly affected by the position of the ??-vinylalkoxy functional group and by the number and position of substituents in the phenoxide moiety. These factors determine the ratio of the homogeneous and heterogeneous steps of the polymerization as a result of the catalyst self-immobilization onto the polymer formed, and also the molecular characteristics of the polymer obtained at 20, 40, and 60°C and ethylene pressure of 0.4 MPa. The possibility and conditions of preparing ultra-high-molecular-weight polyethylene with improved morphology were revealed.     

New silicone hydrogels based on interpenetrating polymer networks comprising polysiloxane and poly(vinyl alcohol) networks

A method for the synthesis of a new silicone hydrogel as a biphase material for soft contact lenses is considered. The method is based on the synthesis of sequential interpenetrating polymer networks (IPN) and includes the following stages: (1) cross‐linked silicone synthesis by the reaction of vinyl‐ and hydride‐containing oligosiloxanes; (2) silicone network saturation with vinyl acetate and cross‐linking monomer followed by UV‐initiated polymerization to form an IPN comprising the silicone and cross‐linked poly(vinyl acetate) (PVAc) network; (3) PVAc network alcoholysis with methanol to obtain silicone hydrogels comprising the silicone and cross‐linked poly(vinyl alcohol) (PVAl). A study of hydrophilic, optical, mechanical, and structural features of the silicone hydrogels showed that optical transparency is achieved for materials with the highest density of silicone network cross‐linking where the size of IPN structural units does not exceed 100 nm. The water content in hydrophilic networks of silicone hydrogel is found to be below the values typical of cross‐linked PVAl, leading to non‐additivity of IPN mechanical properties. Indeed, the elasticity moduli (E) of the hydrophilic and silicone networks are 0.4–0.7 and 0.7–1.8 MPa, respectively, whereas for some IPN this value reaches 3.0 MPa. The optimal parameters of synthesis providing the reduction of E to 0.8–1.6 MPa without deterioration of the required performance characteristics (optical transparency 90–92%, water content 20–39 wt%) are determined. Copyright © 2009 John Wiley & Sons, Ltd.