Tunneling dynamics and spatial correlations of long chain growth in solid-state photochlorination of ethylene at low temperatures

A novel method is described for preparing reactive mixed crystals by vapor deposition in argon and subsequent evaporation of the argon. The kinetics of photochlorination chain reactions of ethylene-chlorine mixtures prepared by this method have been studied by dynamic UV and IR spectroscopy. Activationless chain growth occurs with mean length 260±70 in the temperature range 17–45 K. Chain lengths greater than 100 are observed up to 60–70% conversion to products. Comparison of the experimental data with computer simulations shows that the tunneling reaction is due to formation of a close-packed reaction complex with high amplitude zero-point vibrations which lower the vibrationally adiabatic barrier to reaction. The commensurability of reactant and product crystal lattices results in linear propagation of long chains without accumulation of deformation strain. Spatial correlations caused by nonlinear propagation are considered.     

Chain photohalogenation of ethylene at liquid helium temperatures

Photolysis of a halogen in solid 1:1 molecular complexes of ethylene with chlorine (1) and bromine (2) at 18–70 K led to the formation oftrans-1,2-dihaloethanes by a chain mechanism (with quantum yields of 25–30 for 1 and 10–12 for 2 atT45 K) but molecular addition occurred above 90 K to give thegauche isomer. The rate constant for chain growth is independent of temperature atT45 K, but is described by the Arrhenius equation atT50 K (E ₀ 1 kcal/mole). It is proposed that chain growth occurs by a tunneling reaction of the C₂H₄Hal radical with an Hal₂ molecule at a neighboring lattice site.Institute of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2268–2277, October, 1992.     

Applications of thermal analysis in some solid-state reactions

TG-DTG-DTA has been used to characterize various isomers of CoCl₂·2(CH₃C₆H₄NH₂). Thermal analysis is further used to analyse the binary mixtures of these isomers. DTA recorded after different elapsed times follows the progress of reaction between cobalt chloride and benzocaine where progressively small endotherms are associated with starting materials. The application of thermal analysis to following the solid-solid reactions between metal acetates and 8-hydroxyquinoline was highlighted. The stoichiometry of such reactions was confirmed from the decrease in intensity of an endotherm as one increases the stoichiometry.Thanks are due to Drs. Keshav Chander, K. Kaur, Rajinder Singh and G. S. Chopra for helpful discussions and experimental work.     

Accommodation of the actual solid-state process in the kinetic model function

The degree of coordination between the kinetic information from the thermonalytical measurements and the kinetic theory of the solid-state reactions was investigated through the microscopic study of the thermal dehydration of several inorganic salt hydrates. An accommodation function was applied to the conventional kinetic model functionsf(α), in an attempt to reduce the disagreement between the actual process and the idealized one assumed in formulatingf(α). The significance of the non-integral kinetic exponent in the kinetic model function was discussed with its physico-chemical meanings. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Detection and investigation of oscillations of the rate of radiation-induced solid-state chain reactions at low temperatures

The data on the detection and investigation of rate oscillations of radiation-induced (⁶⁰Co γ-radiation) cryochemical solid-state chain reactions are reviewed. Self oscillation regimes were observed for various reactions (ethylene hydrobromination, polymerization, and copolymerization) in the crystalline and glassy states both in the field of γ-radiation and as the post-effect recorded when the samples were warmed. The recent experimental data on the unusual oscillations of the polymerization rate of crystalline formaldehyde at 5–30 K are discussed. The mechanical factor (brittle disintegration) is proposed to be responsible for these oscillations.     

Statistical correlations of an anyon liquid at low temperatures

Using a proposed generalisation of the pair distribution function for a gas of non-interacting particles obeying fractional exclusion statistics in arbitrary dimensionality, we derive the statistical correlations in the asymptotic limit of vanishing or low temperature. While Friedel-like oscillations are present in nearly all non-bosonic cases at T = 0, they are characterised by exponential damping at low temperature. We discuss the dependence of these features on dimensionality and on the value of the statistical parameter α.     

High-resolution 13C and 43Ca solid-state NMR and computational studies of the ethylene glycol solvate of atorvastatin calcium

We report ⁴³Ca and ¹³C solid-state nuclear magnetic resonance (NMR) spectroscopic studies of the ethylene glycol solvate of atorvastatin calcium. The ¹³C and ⁴³Ca chemical shift and ⁴³Ca quadrupolar coupling tensor parameters are reported. The results are interpreted in terms of the reported X-ray diffraction crystal structure of the solvate and are compared with the NMR parameters of atorvastatin calcium trihydrate, the active pharmaceutical ingredient in Lipitor®. Hartree–Fock and density functional theory calculations of the NMR parameters based on a cluster model derived from the optimized X-ray diffraction crystal structure of the ethylene glycol solvate of atorvastatin calcium are in reasonable agreement with the experimental ⁴³Ca and ¹³C NMR measurables.     

Water-soluble polyesters from long chain alkylesters of citric acid and poly(ethylene glycol)

Long chain aliphatic alcohols have been used as model compounds to develop a preparative method for a water-soluble material, which could be a carrier for triacontanol, a highly hydrophobic plant growth regulator. New polyesters from long chain aliphatic (C = 12, 18 and 22) mono-1-alkyl citrates and poly(ethylene glycol) were synthesized and characterized by NMR spectroscopy. The polyester containing the triacontyl moiety was obtained from mono-1-triacontyl citrate, which was synthesized from the corresponding alcohol extracted from the Agave fourcroydes. The molecular weight of the polyesters depends on experimental conditions during synthesis such as reaction time, atmosphere, catalyst concentration and temperature. The reaction is second order in the early stage of the polyester synthesis. The reaction rate constant is independent of the length of the aliphatic chain, but it decreases with increasing of the poly(ethylene glycol) employed. Turbidity measurements have been used to study the polyester solubility. Solubility characteristics were found to depend on the of poly(ethylene glycol), the aliphatic-chain length and the value of for the polyester. These preparations could potentially be used to release triacontanol.     

Determination of poly(ethylene glycol) 300 in long chain free fatty acid mixtures by reversed-phase high-performance liquid chromatography

A rapid sensitive method has been developed for the detection and quantitation of poly(ethylene glycol) 300 (PEG 300) in long-chain free fatty acid mixtures that requires minimal sample preparation. The PEG 300 was separated from the free fatty acids by RP-HPLC using a water–tetrahydrofuran gradient. PEG and the free fatty acids were detected using evaporative light scattering detection. The minimum detectable level of PEG in a free fatty acid mixture was 0.0125%.     

Crystallization of carboxylic acid salts in poly(ethylene oxide) oligomers at higher temperatures

Many alkali metal carboxylates when dissolved in poly(ethylene oxide) (PEO) oligomers, are phaseseparated by heating. These were revealed to be the crystals of the initially dissolved corresponding salts from the X-ray diffraction patterns. Some acetate salts achieve the lower limit of the lattice energy for phase separation of ordinary inorganic salts by heating in PEO oligomers. These carboxylate salts were therefore expected to show crystallization behavior in PEO oligomers by heating. The effects of cation size, alkyl chain length and molecular weight of PEO on the solubility are summarized. Negative temperature dependence of solubility of these acetate salts is seen in the PEO oligomers only when the salts have long alkyl chains. The salts containing larger cations needed a longer chain length of PEOs for crystallization by heating. These salts with longer alkyl chains showed positive temperautred dependence in lower molecular weight polyethers, but negative temperature dependence in solubility in PEO with molecular weights higher than 400. In PEO₄₀₀, all the carboxylates with longer alkyl chains were phase separated by heating.     

Interconnection between chain growth in the Herington scheme and secondary reactions involving ethylene in the Fischer-Tropsch synthesis

It is shown that C₄₊ hydrocarbons are predominantly formed from intermediates containing three carbon atoms at high values of chain growth probability, but result from interactions of two carbon fragments at low values of chain growth probability. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 178–183, May–June, 2006.     

Glass transition in single poly(ethylene oxide) chain: A molecular dynamics simulation study

Local dynamics of single poly(ethylene oxide) chain in various environments (bulk, film, and isolated systems) has been characterized by the reorientation functions of various backbone bond vectors. Within any observation time, the variations of these reorientation functions with the temperature can be well described by the Kohlrausch?Williams?Watts (KWW) like equation, in which the fitted temperature parameter is identified as the glass transition temperature (T _g). The so‐obtained T _g for that polymer faithfully reveals the effects of the observation time, chain flexibility and vector range on the local dynamics. Furthermore, it is found that the KWW like relation is also applicable to the temperature‐dependence of the fraction of frozen atoms or torsions defined by the trajectory radii of gyration or the conformational transitions. Consequently, different motions lead to different values of T _g for the same system. Despite all, the consistent trend can be yielded, namely, T _g (bulk) > T _g (film) > T _g (isolated), which captures the effects of free surfaces on enhanced dynamics. In addition, dynamics heterogeneity in the systems can be quantitatively revealed. The newly proposed method holds a bright promise to predict the T _g values of complex polymers especially for comparisons. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 178–188     

Infrared spectra of molecular chlorine complexes with acetylene,ethylene and propylene at low temperatures

Infrared spectra of molecular complexes of C₂H₂Cl₂, C₂D₂Cl₂, C₂H₄Cl₂, C₂D₄Cl₂, and C₃H₆Cl₂ were obtained after simultaneous slow deposition of both components on the cooled window of an optical cryostat at 75°K. Chlorine addition reactions to the multiple bond start in these systems at 90–100°K.     

Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures

Many of the spectroscopic features and photophysical properties of carotenoids are explained using a three-state model in which the strong visible absorption of the molecules is associated with an S0 (1(1)Ag-) --> S2 (1(1)Bu+) transition, and the lowest lying singlet state, S1 (2(1)Ag-), is a state into which absorption from the ground state is forbidden by symmetry. However, semiempirical and ab initio quantum calculations have suggested additional excited singlet states may lie either between or in the vicinity of S1 (2(1)Ag-) and S2 (1(1)Bu+), and some ultrafast spectroscopic studies have reported evidence for these states. One such state, denoted S*, has been implicated as an intermediate in the depopulation of S2 (1(1)Bu+) and as a pathway for the formation of carotenoid triplet states in light-harvesting complexes. In this work, we present the results of an ultrafast, time-resolved spectroscopic investigation of a series of open-chain carotenoids derived from photosynthetic bacteria and systematically increasing in their number of pi-electron carbon-carbon double bonds (n). The molecules are neurosporene (n = 9), spheroidene (n = 10), rhodopin glucoside (n = 11), rhodovibrin (n = 12), and spirilloxanthin (n = 13). The molecules were studied in acetone and CS2 solvents at room temperature. These experiments explore the effect of solvent polarity and polarizability on the spectroscopic and kinetic behavior of the molecules. The molecules were also studied in ether/isopentane/ethanol (EPA) glasses at 77 K, in which the spectral resolution is greatly enhanced. Analysis of the data using global fitting techniques has revealed the ultrafast dynamics of the excited states and spectral changes associated with their decay, including spectroscopic features not previously reported. The data are consistent with S* being identified with a twisted conformational structure, the yield of which is increased in molecules having longer pi-electron conjugations. In particular, for the longest molecule in the series, spirilloxanthin, the experiments and a detailed quantum computational analysis reveal the presence of two S* states associated with relaxed S1 (2(1)Ag-) conformations involving nearly planar 6-s-cis and 6-s-trans geometries. We propose that in polar solvents, the ground state of spirilloxanthin takes on a corkscrew conformation that generates a net solute dipole moment while decreasing the cavity formation energy. Upon excitation and relaxation into the S1 (2(1)Ag-) state, the polyene unravels and flattens into a more planar geometry with comparable populations of 6-s-trans and 6-s-cis conformations.     

The reaction of furfuryl alcohol resins with hexamethylenetetramine: A 13C and 15N high-resolution solid-state NMR study

The reactions between furfuryl alcohol (FA)/poly(furfuryl alcohol) (PFA) and hexamethylenetetramine (HMTA) have been studied by ¹³C and ¹⁵N high-resolution solid-state NMR techniques. Highly crosslinked polymer networks similar to those obtained from the thermal curing of FA resins under acidic condition are formed. Possible reaction pathways are postulated on the basis of changes of chemical structures during the curing; α-substituted furfurylamines are shown to be the initial intermediates. Their further reactions with FA/PFA, together with thermal decomposition, produce methylene linkages between furan rings, resulting in chain extension and crosslinking, which occurs at both the methylene linkages and the 3- or 4-C of furan rings. Various side-products such as amines, imines, amides, imides, and nitriles are also formed during the reactions, and some of these can remain in the resins up to 205°C. The crosslinked network can be heterogeneous with different structures on nanometer scales when higher oligomers of FA resins react with HMTA. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2233–2243, 1997     

Molecular interactions in poly(ethylene glycol)-water mixtures at various temperatures: density and isentropic compressibility study.

The densities and sound velocities of mixtures of water with poly(ethylene glycol), poly(ethylene glycol) monomethylether, and poly(ethylene glycol) dimethylether with mean molar weights between 250 and 500 have been measured as a function of mixture composition and temperature between 10 and 40 degrees C. Isentropic compressibilities are derived from the data and are compared to those for the ethylene glycol/water system and for other organic solvent/water mixtures. Relative minima in the mixture volume to ideal volume ratio and in the dependence of the compressibility upon mixture composition are discussed in terms of the conformational variability of the chainlike oligomers, of hydrogen-bonded networks, and of water clusters between the oligomer chains.     

Thermodynamic properties of surfactant sodium n-heptyl sulfonate in water and in aqueous solutions of poly(ethylene glycol) at different temperatures

The volumetric, compressibility and electrical conductivity properties of sodium n-heptyl sulfonate (C₇SO₃Na) in pure water and in aqueous poly(ethylene glycol) (PEG) solutions were determined at different temperatures below and above the micellar composition range. At each temperature, the infinite dilution apparent molar volumes of the monomer and micellar state of C₇SO₃Na in aqueous PEG solutions respectively are smaller and larger than those in pure water. However, the values of the infinite dilution apparent molar isentropic compressibility of both monomer and micellar states of C₇SO₃Na in aqueous PEG solutions are larger than those in pure water. Thermodynamic parameters of micellization of investigated surfactant in water and in aqueous solutions of PEG at different temperatures were estimated and it was found that the micelle formation process is endothermic and therefore, this process must be driven by entropy increase. The calculated Gibbs free energies of micellization for aqueous PEG solutions are more negative than those for pure water and become more negative by increasing temperature. The variation of the critical micelle concentration (CMC) of C₇SO₃Na in water and in aqueous PEG solutions with temperature was obtained and a comparison between the CMC of C₇SO₃Na obtained from different thermodynamic properties was also made.     

Evidence of random chain scissions at low temperatures in the thermal degradation of anionic polystyrenes

In the thermal degradation of some anionic polystyrene samples chain scission was found to occur in the temperature range 180–220°C. The resulting polymer molecules thereafter remain stable up to about 280°C, above which strong reductions occur in the degree of polymerization. It is shown that the low temperature degradation is due to the presence of a small fraction of weak links, which could be tentatively attributed to some oxidation of the polymers.     

Solid-state photochromism of chromenes: enhanced photocoloration and observation of unstable colored species at low temperatures

Solid-state photochromism of benzopyrans and naphthopyrans (chromenes) was investigated in the temperature range between 300 and 80 K. Variable-temperature diffuse reflectance spectroscopy of microcrystalline powders showed that the extent of photocoloration was greatly enhanced at low temperatures. All the chromenes examined exhibited solid-state photochromism at low temperatures, even when they showed little or no photocoloration at room temperature. The solid-state photochromic properties of the chromenes were quite similar to those reported for analogous photochromic compounds of spiropyrans and spirooxazines, which indicates that these classes of compounds are generally photochromic even in the solid state. Photobleaching reactions of the colored merocyanine forms proceeded at low temperatures through the formation of a colorless intermediate, instead of directly resuming the original closed form. In addition to two stable planar merocyanine forms, which are usually observed in the photochromic reactions in solution, photoreactions at low temperatures allowed us to observe unstable colored species, which were tentatively assigned as nonplanar cisoid forms, and were stabilized in the solid state at low temperatures.