The use of NMR for determination of new structures in irradiated TFE/PMVE fluoropolymers

The radiation chemistry of two TFE/PMVE copolymers with TFE mole fractions of 0.66 and 0.81 has been studied under vacuum using ⁶⁰Co γ-radiation over absorbed dose ranges up to 4.2 MGy. The radiolysis temperature was 313 K for both TFE/PMVE copolymers. New structure formation in the copolymers was identified by solid-state ¹⁹F NMR and the G-values for new chain ends of 2.1 and 0.5 and for branching sites of 0.9 and 0.2 have been obtained for the TFE/PMVE with TFE mole fractions of 0.66 and 0.81, respectively. The relative yields of –O–CF₃ and –CF₂–CF₃ chain ends were found to be proportional to the copolymer composition, but the yields of the –CF₂–CF₃ chain ends and –CF– branch points were not linearly related to the composition, rather they were correlated with the radical yields measured at 77 K.     

Molecular structure and internal rotation potential of perfluoro (2,4-dimethyl-3-oxa-2,4-diazapentane), (CF3)2N–O–N(CF3)2

Ab initio quantum chemical calculation were performed on R₂N–O–NR₂ type (R=H, F, CH₃ and CF₃) molecules, using the HF, B3LYP and MP2/6-31G* levels of theory. The equilibrium structures and the internal rotation potentials have been determined. Three stable conformers were found for R=H, F and CH₃ while only two in case of R=CF₃. The rotation potential energy curves do not change significantly upon fluorination. The calculations suggests that in the ED measurement of the title compound the NC and NO bond length might have been interchanged.     

Vibrational frequencies and structural determination of 1,1-difluoro-1,2-propadiene

The normal mode frequencies and corresponding vibrational assignments of 1,1-difluoro-1,2-propadiene in C_2v symmetry are examined theoretically using the 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of 11 types of motion (C=C stretch, C–H stretch, C–F stretch, CH₂ scissors, CF₂ scissors, CH₂ wag, CF₂ wag, CH₂ rock, CF₂ rock, CF₂ twist, and C=C=C bend) predicted by a group theoretical analysis. Comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors is derived. Predicted infrared intensities and Raman activities are reported. Predicted normal mode frequencies of 1,1-difluoro-1,2-propadiene-d₂ are reported.     

Interaction of antitumor drug Sn(CH3)2Cl2 with DNA and RNA

Sn(CH₃)₂Cl₂ exerts its antitumor activity in a specific way. Unlike anticancer cis-Pt(NH₃)₂Cl₂ drug which binds strongly to the nitrogen atoms of DNA bases, Sn(CH₃)₂Cl₂ shows no major affinity towards base binding. Thus, the mechanism of action by which tinorganometallic compounds exert antitumor activity would be different from that of the cisplatin drug. The aim of this study was to examine the binding of Sn(CH₃)₂Cl₂ with calf thymus DNA and yeast RNA in aqueous solutions at pH 7.1–6.6 with constant concentrations of DNA and RNA and various molar ratios of Sn(CH₃)₂Cl₂/DNA (phosphate) and Sn(CH₃)₂Cl₂/RNA of 1/40, 1/20, 1/10, 1/5. Fourier transform infrared (FTIR) and UV–visible difference spectroscopic methods were used to determine the Sn(CH₃)₂Cl₂ binding mode, binding constant, sequence selectivity and structural variations of Sn(CH₃)₂Cl₂/DNA and Sn(CH₃)₂Cl₂/RNA complexes in aqueous solution. Sn(CH₃)₂Cl₂ hydrolyzes in water to give Sn(CH₃)₂(OH)₂ and [Sn(CH₃)₂(OH)(H₂O)_n]⁺ species. Spectroscopic evidence showed that interaction occurred mainly through (CH₃)₂Sn(IV) hydroxide and polynucleotide backbone phosphate group with overall binding constant of K(Sn(CH₃)₂Cl₂–DNA)=1.47×10⁵ M⁻¹ and K(Sn(CH₃)₂Cl₂–RNA)=7.33×10⁵ M⁻¹. Sn(CH₃)₂Cl₂ induced no biopolymer conformational changes with DNA remaining in the B-family structure and RNA in A-conformation upon drug complexation.     

Direct dynamics studies on the hydrogen abstraction reactions CF3O+CH4(CD4)→CF3OH(CF3OD)+CH3(CD3)

The dynamics properties of the hydrogen abstraction reaction CF₃O+CH₄→CF₃OH+CH₃ are studied by dual-level direct dynamics method. Optimization calculations are preformed by B3LYP and MP2 with the 6-311G(d,p) basis set, and the single-point calculations are done at the multi-coefficient correction method based on quadratic configuration interaction with single and double excitations (MC-QCISD) method. The rate constants are evaluated by canonical variational transition-state theory with a small-curvature tunneling correction over a wide range of temperature 200–2000 K. The agreement between theoretical and experimental rate constants is good in the measured temperature range. The calculated results show that the variational effect is small and almost neglected over the whole temperature range, whereas, the tunneling correction plays a role in the lower temperature range. The kinetic isotope effect for the reaction is ‘normal’. The value of k_H/k_D is 2.38 at room temperature and it decreases with the temperature increasing.     

Reactions of tetrakis(trifluoromethyl) diphosphine and bis(trifluoromethyl) phosphine with ruthenium carbonyl clusters; X-ray structure of tetraruthenium carbonyl cluster derivatives

Reaction of [Ru₃(CO)₁₂ with (CF₃)₂P---P(CF₃)₂ in p-xylene at 140°C yielded the compounds [Ru₄(CO)₁₃{μ-P(CF₃)₂}₂] (1), [Ru₄(CO)₁₄{μ-P(CF₃)₂}₂] (2) and [Ru₄(CO)₁₁{μ-P(CF₃)₂}₄] (3). Reaction with [(μ-H)₄Ru₄(CO)₁₂] under similar conditions yielded [(μ-H)₃Ru₄(CO)₁₂{μ-P(CF₃)₂}] (4). All four compounds have been characterised by X-ray crystallography. The fluxional behaviour of the hydrides in 4 has also been studied by variable-temperature NMR spectroscopy. Compounds 1, 2 and 4 were also obtained from the reactions of Ru₃(CO)₁₂ with (CF₃)₂PH in dichloromethane at 80°C.     

Dynamic chirality in selected diaryl methane containing drugs. An exploratory ab initio conformational study

Diaryl methane molecules (Ar–CH₂–Ar) represent double rotor conformational problems. The simplest diaryl methane, diphenyl methane (Ph–CH₂–Ph), governs certain symmetric conformational potential energy surface (PES) topology. With the replacement of one of the phenyl groups by a heterocyclic moiety, the PES topology may change dramatically. The induction of point-chirality, in the prochiral CH₂ group, by axis-chirality or plane-chirality is explored within the framework of ‘dynamic chirality’.     

3(1,3-Heterazolidin-3-yl-methyl)-1,3-oxazolidines and their reduction with borane–THF

Preparation of bis-heterazolidines bonded by a CH₂, CH₂–S–CH₂ or CH₂SCH₂SCH₂ groups through their nitrogen atoms is reported: 3-(1,3-oxazolidin-3-ylmethyl)-1,3-oxazolidine 1, 3-(4,4-dimethyl-1,3-oxazolidin-3-ylmethyl)-1,3-oxazolidine 2, 3-(1,3-diazolidin-3-ylmethyl)-1,3-diazolidine 3, 3-(1,3-thiazolidin-3-ylmethyl)-1,3-thiazolidine 4, 3-(1,3-thiazolidin-3-ylmethylsulfanylmethyl)-1,3-thiazolidine 5 and 3-(1,3-oxazolidin-3-ylmethylsulfanylmethyl-sulfanylmethyl)-1,3-oxazolidine 6. The solid state structures of 4 and 5 were determined by X-ray diffraction analyses. BH₃–THF reduction reactions of compounds 1–6 were investigated. N→BH₃ mono- and di-adducts of 1–6 were prepared and their structures calculated (ab initio 3-21G*).     

Surfactants having polyfluoroalkyl chains. II. Syntheses of anionic surfactants having two polyfluoroalkyl chains including a trifluoromethyl group at each tail and their flocculation-redispersion ability for dispersed magnetite particles in water

Anionic surfactants having two polyfluoroalkyl chains per molecule, i.e. the sodium salt of bis(1H, 1H, 2H,2H-heptadeca-fluorodecyl)-2-sulfosuccinate, CF₃(CF₂)₇(CH₂)₂OCOCH₂CH(SO₃Na)COO(CH₂)₂(CF₂)₇CF₃, the sodium salt of bis(1H, 1H, 2H, 2H-tridecafluoro-octyl)-2-sulfosuccinate, CF₃(CF₂)₅(CH₂)₂OCOCH₂CH(SO₃Na)COO(CH₂)₂(CF₂)₅CF₃, and the sodium salt of bis(1H, 1H, 2H, 2H-nonafluorohexyl)-2-sulfosuccinate, CF₃(CF₂)₃(CH₂)₂OCOCH₂CH(SO₃Na)COO(CH₂)₂(CF₂)₃CF₃, have been prepared from maleic anhydride, the corresponding alcohols possessing a polyfluoroalkyl chain and sodium hydrogen sulfite. The flocculation and redispersion abilities of these surfactants for dispersed magnetic particles in water have been examined to investigate the effect of the chain length. It was found that this ability was enhanced by an increase in the chain length. The contact angles for water for pelleted surface-modified magnetite have been measured. In order to compare this ability and the contact angles, data for other fluorinated surfactant have been obtained. The Kraff point, the surface tension and the pNa of the aqueous surfactant solutions have also been measured.     

Proton transfer between hydrogen halides and dimethylether in nitrogen matrices. An example of infrared-induced transfer

The infrared absorption of mixtures of dimethyl ether and hydrogen halide (HX) in nitrogen at 13 K display relatively narrow bands in the range 650–800 cm⁻¹ with an isotopic ratio ν_H/ν_D larger than 1.4 and weakly halogen dependent; these features are assigned to the antisymmetric O…H…O stretching within the [(CH₃)₂ O…H…O(CH₃)₂]⁺X⁻ ion pair. With HI—ether mixtures, the intensity of the 660 cm⁻¹ band decreases under infrared irradiation of the matrix, which might be due to the transfer of the proton back to the I⁻ anion.     

Homo-metathesis of vinylsilanes catalysed by ruthenium carbene complexes

Effective homo-metathesis of a series of dichloro-substituted vinylsilanes H₂C = C(H)SiCl₂R (where R = Me, OSiMe₃, C₆H₅, C₆H₄–Me-4, C₆H₄–CF₃-4) in the presence of second generation Grubbs catalyst [Cl₂(PCy₃)(IMesH₂)Ru(=CHPh)] (I) and Hoveyda–Grubbs catalyst (II) leads to selective formation of E-1,2-bis(silyl)ethenes and ethene. On the basis of the results of experiments with deuterium-labelled reagents, a metallacarbene mechanism has been suggested for these reactions.     

A new assignment of IR vibrational modes in mullite

A new assignment of IR absorption bands of mullite is presented on the basis of empirical studies in the 1400–400 cm⁻¹ vibrational range of mullite-type compounds in the systems Al₂O₃–SiO₂, Al₂O₃–GeO₂, Ga₂O₃–GeO₂, and Al₂O₃–Me₂O, Ga₂O₃–Me₂O (Me=Na, K, Rb). The powder samples were prepared by heat treatment of sol–gel derived precursor powders and by reaction sintering of oxide powders. The FTIR powder spectra of Al–Si, Al–Ge, and Ga–Ge mullite compounds are characterized by three band groups, designated as (a), (b) and (c). Due to the lack of group (a) bands in the alkaline aluminate and gallate spectra, this high-energetic band group is assigned to Si---O and Ge---O stretching vibrations. Group (b) bands are essentially determined by Al---O and Ga---O stretching vibrations with Al and Ga on T sites in tetrahedral coordination and by T---O---T bending modes, while the low-energetic group (c) bands are due to Al---O and Ga---O stretching vibrations in octahedral structural units. Details of the vibrational modes are discussed on the basis of the deconvoluted spectra.     

Chemical reactivity of two-photon excited trimethylsilylacetylene in aerosol particle formation with acrolein

Under irradiation with N₂ laser light, a gaseous mixture of trimethylsilylacetylene (ethynyltrimethylsilane) (TMeSiA) and acrolein (AC) produced sedimentary aerosol particles with a mean diameter of 1.0 μm. Nucleation process of the aerosol particles was studied by measuring monitor (He–Ne laser) light intensity scattered by the aerosol particles as formed under N₂ laser light irradiation. With increasing partial pressure of TMeSiA, the nucleation reaction of aerosol particles was accelerated due to additional generation of reactive species from TMeSiA molecules by a two-photon process. FT-IR spectra of the sedimentary particles showed that TMeSiA molecules were incorporated into polymerization reaction of AC by forming –Si–O–C– bond from R(CH₃)₂Si radicals. Two-photon processes of both AC and TMeSiA molecules under N₂ laser light irradiation were briefly discussed.     

A non-empirical molecular orbital study on loewenstein''s rule and zeolite composition

The role of the “aluminum avoidance rule” in zeolite frameworks and its relation to the electronic structure and stability of various structural units of alumosilicates were studied by non-empirical SCF—MO techniques. Al—O—Al-type linkages are unstable according to the calculations. The presence of cations in the neighbourhood of T₁—O—T₂ bridges (T₁, T₂ = Si or Al) is the least stabilizing when T₁ = T₂ = Al.     

Synthesis of methyltrioxorhenium(VII) arylamine complexes and mono- and bis(ortho)-chelated arylaminorhenium(VII) trioxides

From the reaction of MeReO₃ with the neutral arylamine C₆H₅CH₂NMe₂ and the aryldiamine C₆H₄(CH₂NMe₂)₂−1,3, have been isolated in good yields the 1/1 adduct complex [MeReO₃ · C₆H₅CH₂NMe₂], 1, and the 2/1 adduct complex [(MeReO₃)₂ · C₆H₄(CH₂NMe₂)₂− 1,3], 2, respectively. The X-ray molecular structure of 2 shows that both rhenium centres have a trigonal bipyramidal geometry and in the axial positions of each rhenium centre are one of the NMe₂ units of the aryldiamine ligand and a methyl group. The mono(ortho)-chelated arylaminorhenium trioxide complex [ReO₃(C₆H₄CH₂NMe₂−2], 3, can be synthesized by a transmetallation reaction of ClReO₃ with [ZnC₆H₄CH₂NMe₂−2₂] in a 2:1 molar ratio. In a similar way the bis(ortho)-chelated arylaminorhenium trioxide complex [ReO₃C₆H₃(CH₂NMe₂)₂−2,6], 4, can be synthesized by addition of a mixture of [Li₂C₆H₃(CH₂NMe₂)₂−2,6₂] and ZnCl₂ to ClReO₃. Complexes 3 and 4 have been isolated as white solids in 66% and 81% yields respectively. The rhenium centre in complex 4 has a bicapped tetrahedral geometry in which the monoanionic C₆H₃(CH₂NMe₂)₂−2,6⁻ ligand is pseudo-facially bonded with a characteristic N1-Re-N2 angle of 107.7(3)°, a Re-C_ipso bond length of 2.112(11) Å and Re-N1 and Re-N2 bond lengths of 2.518(9) Å and 2.480(8) Å respectively.     

The hydrogen-bond network in propylene-glycol studied by Raman spectroscopy

In the present work, we report a polarized Raman study versus temperature of the complex O–H stretching vibrational band (3800–3000 cm⁻¹) performed in a glass forming liquid, namely propylene-glycol (PG), with chemical formula given by H[OCH(CH₃)CH₂]OH. The spectra were collected in bulk and confined state within a sol–gel controlled porous glass having highly interconnected 25 Å diameter pores and characterized by a huge number of silanol groups (Si–OH), able to interact with PG molecules via hydrogen bond. The goal was to investigate how the hydrophilic nature of the surface influenced the molecular mobility of this hydrogen-bonded system, by monitoring intra- and inter-molecular host–host and host–guest interactions. The analysed O–H spectral region was decomposed into Gaussian symmetrical profiles, each of them associated to a well-defined aggregate, triggered by the presence of H-bond. Passing from the bulk state to the confined one, a clear change of the dynamical properties has been revealed and related to the interactions with the surface. The observed results were discussed on the basis of current models for associated liquids.     

The ν(OH/OD) band shape of strong hydrogen bonded dimers of phosphinic acids. Phenomenology and formation models

The infrared spectra of phosphinic acid R₂POOH dimers (R=CH₃, CH₂Cl, C₆H₅) have been studied in CCl₄ and CH₂Cl₂ solutions (T=300 K). The infrared spectra of deuterated R₂POOD dimers (R=CH₃, CH₂Cl) were also studied in the gas phase (T=400–550 K) and solid state (T=100–300 K). They are compared with previously studied spectra of the light (non-deuterated) dimers in the gas phase, in the solid state and in low-temperature argon matrices (T=12–30 K) in the 4000–400 cm⁻¹ spectral region. It is found that the strong and broad ν(OH) dimer bands have similar shapes, nearly equal values of bandwidth and low-frequency shift, and possess the Hadzi ABC structure irrespective of the type of acid, significant differences of dimerization enthalpies, influence of solvent, the type of H-bonded complexes (cyclic dimers in the gas phase, in solutions, and in inert matrices, and infinite chains in the solid state), and temperature in the range 12–600 K. Isotopic ratio of the first moments of light and deuterated acid bands has been measured. Analysis of the ν(OH/OD) band of hydrogen bonded dimers of phosphinic acids shows that the interaction between the two intermolecular bonds O–HOP in a cyclic complex plays virtually no role in the mechanism of the ν(OH/OD) band formation; the shape of ν(OH/OD) band is controlled mainly by the POOH(D)O fragment; and the band shape of strong hydrogen bonded complexes is formed by a number of vibrational transitions from the ground state to different combination levels in the region 3500–1500 cm⁻¹.     

Polymer chemistry. Part 1. Model compounds related to hexafluoropropenevinylidene fluoride elastomer

Model compounds related to the important elastomer derived from CH₂2=CF₂/CFCF₃ are synthesised from telomers (CF₃)₂CF(CH₂CF_2nI, by coupling and by fluorodeiodination reactions. These models, in reactions with bases, give information relating to mechanism of cross-linking of the polymer and indications of factors that limit its working life. Novel use of SbF₅ for dehydrofluorination in synthesis of fluorinated mono-enes and di-enes is described.     

Filling of antibonding orbitals—II Chemical bond properties

Antibonding effects, which accompany double-bonding in saturated compounds, account for many chemical bond lengths which are anomalous on the basis of electronegativity. Double-bonding influences the Pauling Electronegativity values of N, O, F, Al and Si and also widens the interbond angles in molecules such as (CH₃)₃N, (CF₃)₃N, (CH₃)₂O and (CF₃)₂O.