An investigation of the thermolysis mechanism of model urethanes

The products of pyrolysis in a helium atmosphere of a model urethane foam based on PAPI and propoxylated trimethylol propane were investigated by using GC/MS and GC/CIMS. Chemical-ionization mass spectrometry was used because it produces primarily protonated molecular ions (M + 1) with little fragmentation which facilitated the identification of the polyol decomposition products. Identification of the polyol pyrolysis fragments has led to the formulation of a detailed polyol thermolysis mechanism. This mechanism shows the polyol to decompose by a systematic route of reactions rather than by a random breakdown.     

Access to nonisocyanate poly(thio)urethanes: A comparative study

This article describes the synthesis of new cyclic compounds able to react with amines to get nonisocyanate polyurethanes (NIPUs). The contribution of the most studied five‐membered cyclic carbonate was compared to five‐membered cyclic dithiocarbonate analogous and to a six‐membered cyclic carbonate. Difunctional reactive species were obtained by a simple substitution reaction or an efficient thiol–ene coupling reaction. The products, obtained with high yields, were characterized by 1H NMR, 13C NMR, and Fourier tansform infrared spectroscopy analysis. The dicyclocarbonates were then used to synthesize NIPUs by step growth polymerization with several diamines. These materials exhibited glass transition temperatures from 19 to ?29 °C, molar mass from 1800 to 20,400 g mol^?1, and a 20% mass loss temperature (T_d = 20%) between 249 and 296 °C. Such materials are interesting candidates for coating applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3284–3296     

Spectroscopic kinetic study of the interaction of urethanes with amines

The exchange reactions of phenyl-N-phenylurethane with amines varying in structure and nature have been investigated in o-dichlorobenzene. In the absence of a catalyst and proton-donating compound, the unimolecular decomposition of phenyl-N-phenylurethane into isocyanate and alcohol takes place at a noticeable rate starting at 250°C. The exchange reactions at 60–80°C proceed as a direct exchange between the urethane and the proton donor and are second-order up to high conversions, practically until the disappearance of the entire urethane. The activation energies and apparent rate constants of the exchange reactions of phenyl-N-phenylurethane with various amines have been determined. The results have been explained in terms of the dependence of kinetic parameters of the reaction on the amine nature, structure, and nucleophilicity, on the steric accessibility of the amino group, and on the molecular organization of the solution.     

A chemical and spectroscopic study of albonoursin

Summary 1. A direct comparison of albonoursin with component 2 isolated from the producing agent of phalamysin (a mutant ofActinomyces noursei) has established their identity.2. Phenylpyruvic acid and acetone have been identified as products of the acid decomposition of albonoursin.3. The presence of the following groupings in the albonoursin molecule has been shown: C₆H₅-CH=C-C, (CH₃)₂ CH-C= or (CH₃)₂C=C, two amide groups, and two hydrogen atoms readily capable of being replaced by halogen atoms (under the action of Br₂ or SOCl₂).4. There is no malonamide group in albonoursin.Khimiya Prirodnykh Soedinenii, Vol. 1, No. 6, pp. 395–400, 1965     

A Raman spectroscopic study of synthetic giniite

The mineral giniite has been synthesised and characterised by XRD, SEM and Raman and infrared spectroscopy. SEM images of the olive-green giniite display a very unusual image of pseudo-spheres with roughened surfaces of around 1-10microm in size. The face to face contact of the spheres suggests that the spheres are colloidal and carry a surface charge. Raman spectroscopy proves the (PO4)3- units are reduced in symmetry and in all probability more than one type of phosphate unit is found in the structure. Raman bands at 77K are observed at 3380 and 3186cm-1 with an additional sharp band at 3100cm-1. The first two bands are assigned to water stretching vibrations and the latter to an OH stretching band. Intense Raman bands observed at 396, 346 and 234cm-1are attributed to the FeO stretching vibrations. The giniite phosphate units are characterised by two Raman bands at 1023 and 948cm-1 assigned to symmetric stretching mode of the (PO4)3- units. A complex band is observed at 460.5cm-1 with additional components at 486.8 and 445.7cm-1 attributed to the nu(2) bending modes suggesting a reduction of symmetry of the (PO4)3- units.     

A new cytosine-copper paramagnetic complex spectroscopic study

Two different copper complexes with cytosine molecules are formed in the process of crystal growth from the aqueous solution with traces of copper. One of them is diamagnetic, turning into paramagnetic upon ionizing irradiation (complex I). The other, the subject of the present study, is paramagnetic (complex II) as prepared. For complex II, EPR spectra demonstrate that the copper ion is coordinated with one nitrogen atom and three oxygen atoms. On the basis of the detailed EPR spectroscopic analysis and quantum-chemical calculations (in the DFT approach) the model of the complex has been proposed. Both experimental data and the theoretical results support the model with the copper atom, located between the two cytosine ribbons, ligated to a nitrogen and an oxygen atom from two opposing cytosine molecules and two oxygen atoms from water molecules. For complex II the Raman spectra demonstrated concerted restructuring of the hydrogen bonding in the cytosine crystal matrix upon insertion of copper ions.     

A spectroscopic study of the protonation of acylferrocenes

Infrared spectra of the products formed in the reaction between hydrogen chloride (and deuterium chloride) and the bases formylferrocene, acetylferrocene and 1,2-(α-ketotetramethylene)-ferrocene have been studied. The results suggest that these bases are much stronger than arylketones with a related skeletal structure and that at least two cationic conjugate acids are formed. The importance of the mutual interaction of the iron and oxygen atoms in stabilizing the protonated complexes is discussed.     

A vibrational spectroscopic study on 1,1,2-tribromethane

On the basis of new data on the Raman spectra of solid and gaseous 1,1,2-tribromoethane a revised vibrational assignment is suggested.     

The physical crosslinking of polyurethane elastomers studied by X-ray investigation of model urethanes

Polyurethane elastomers extended with aliphatic glycols or diamines, show a characteristic fluctuation in their thermal and hydrothermal properties which is dependent on the number of CH₂ groups in the chain extender (even or odd).The causes of this behavior are examined in the following report using X-ray crystallographic analyses of single crystals of model urethanes. These model compounds were prepared by reaction between diphenylmethane -4-mono-isocyanate and glycoles of the HO-(CH₂)_n-OH structure withn=2 to 6.Whilst strain-free hydrogen bonds can form between neighboring molecules in urethanes with even chain extenders, significant strains occur in urethanes containing odd chain extenders which result in reduced stability of the physical crosslinking system.In memoriam to Prof. Dr. Dr. h. c. mult. Otto Bayer.     

A Raman spectroscopic study of N,N-dimethylacrylamide

A comprehensive Raman spectroscopic study of N,N-dimethylacrylamide has been carried out to produce new vibrational assignments for the molecule. The provision of polarization data for the first time has enabled the correction of several assignments for the normal modes previously reported in the literature to be made.     

A Raman spectroscopic study of photochromic benzothiazolium dyes

Resonance Raman spectra using several excitation wavelengths have been obtained in the region 300–1750 cm⁻¹ for two photochromic benzothiazolium dyes containing a crown ether ring. Bands arising from both cis- and trans-isomers have been distinguished by comparing the spectra observed at different resonances and under different sample conditions. Preliminary assignments of the bands have been made, allowing insight into the changes in structure and bonding which occur on photoisomerization.     

A spectroscopic study of some oxometal ion complexes

The i.r. spectra (4000-250 cm⁻¹) of Cs₃[VO(CN)₅], [(C₂H₅)₄N]₃[VO(NCS)₅], and K₃ [ReO₂(CN)₄·2H₂O have been obtained and empirical band assignments made. From a study of the v (CN) frequency it was possible to ascertain that metal-cyanide π-bonding is probably more important in VO(CN)₅³⁻ than ReO₂(CN)₄³⁻. Infrared evidence confirms the presence of N-bonded thiocyanate in VO(NCS)₅³⁻. The electronic spectra of the mulled solidssuggest that the lowest-energy transition in symmetrical VO²⁺ and trans-ReO₂⁺ systems is similar.     

A Raman spectroscopic study of selected natural jarosites

Raman spectroscopy has been used to characterise the jarosite group of minerals of formula Mn(Fe3+)6(SO4)4(OH)12 where M may be K, (NH4)+, Na, Ag or Pb and where n = 2 for monovalent cations and 1 for the divalent cations. Raman spectroscopy proved useful for mineral identification especially where closely related minerals crystallise out from solutions where paragenetic relationships exist between the minerals. The band position of the SO4(2-) symmetric stretching mode proved to be a function of the ionic radius of the cation. The bending modes show a slight dependence. The spectra of the natural samples can be complex. This complexity is attributed to the incorporation of low levels of other cations into the structure.     

A Raman spectroscopic study of indolinium steryl dyes

Resonance Raman spectra have been obtained in the region 400–1700 cm⁻¹ for several indolinium steryl dyes under various experimental conditions. The changes in vibrational frequencies have been correlated with changes in the UV—vis absorption maxima observed previously and which are due to solvent polarity variations, the complexation of the dye molecules containing a crown ether ring with Mg²⁺, and the variations in molecular structure. Preliminary assignments of the observed bands to particular vibrations are made.     

An infrared spectroscopic study of hydrogen bonding in ethyl phenol: A model system for polymer phenolics

A detailed analysis of the bands appearing in the OH stretching region of the infrared spectrum of ethyl phenol solutions is presented. In cyclohexane solutions, the band due to “free” (non-hydrogen-bonded groups) contains overlapping contributions from both monomeric and end-group species. Other assignments are made on the basis of whether the proton and oxygen in a particular OH group are both involved in hydrogen bonds (as “donors” and “acceptors”, respectively), or if only the proton is acting as a donor. The strongest band in the spectra obtained at the highest concentration of ethyl phenol is due to OH groups present in linear chains of hydrogen-bonded OH groups (as recognized in numerous other studies), but a band due to cyclic trimers has also been identified. The assignment of other modes is more uncertain and various possibilities are discussed. In toluene solutions, assignments are more complicated, because bands due to OH–π hydrogen bonds are observed instead of free groups. Finally, the data from cyclohexane solutions was used to calculate equilibrium constants capable of describing the distribution of species present. A new methodology for determining the equilibrium constant describing association in the form of dimers is described.     

Radiation induced polymerization of isoprene: A spectroscopic study

Isoprene polymerizes under the action of γ-radiation from a ⁶⁰Co source yielding a low molecular weight polyisoprene which remains soluble in the unreacted monomer. The electronic absorption spectrum of polyisoprene oligomer in isoprene monomer has been explained using squalene, a polyisoprene hexamer, as model compound. The radiation chemical yield for polyisoprene formation has been estimated from both gravimetric and spectrophotometric data pertaining the amount of polymer formed. An average G value of 35 molecules/100 eV has been determined suggesting that the polymerization mechanism involves free radicals. The chemical structure of the resulting polyisoprene radio-oligomer has been determined by FT-IR spectroscopy and found identical to that of a reference polyisoprene sample prepared by a chemically-initiated free radical polymerization process. The structure determination by FT-IR spectroscopy has been reported in detail.