Neutron scattering studies of solid-state polymorphism in dimethyl butanol glass formers

Inelastic incoherent neutron scattering (IINS) and neutron powder diffraction (NPD) studies have been performed for two dimethyl 1-butanols and two dimethyl 2-butanols with CH₃ side molecular groups. Low-temperature vibrational density of states confirmed solid-state polymorphism detected by calorimetric methods, i.e., existence of crystalline and ODIC phases for all isomers, orientationally disordered glass for 2,2-DM 1-B and 3,3-DM 2-B, and glass of isotropic phase for 3,3-DM 1-B. Difference in vibrational density of states between glass and the ordered crystal has shown the so-called Boson peak. Influence of the OH group position in the molecules on their vibrational dynamics up to 50 meV is discussed.     

Structural and morphological characterization of chemically deposited silver films

Silver thin films were deposited on glass slide substrates at room temperature by the chemical bath deposition (CBD) technique, using silver nitrate (AgNO₃) as Ag⁺¹ source and triethanolamine [(N(CH₂CH₂OH)₃)] as the complex reductor agent. We determined the conditions of the CBD process to obtain homogeneous, opaque silver films with good adhesion to the substrate and white coloration. The silver films were studied by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The results show that the films are composed of several layers with different morphology depending on the deposition time. In all the cases, the crystalline structure of the films was the face cubic centered phase with a moderate [111] texture. Strains and stresses were calculated by the Vook-Witt grain interaction model.     

Gas‐phase oxidation of CH2 = C(CH3)CH2Cl initiated by OH radicals and Cl atoms: kinetics and fate of the alcoxy radical formed

Relative kinetics of the reactions of OH radicals and Cl atoms with 3‐chloro‐2‐methyl‐1‐propene has been studied for the first time at 298 K and 1 atm by GC‐FID. Rate coefficients are found to be (in cm³ molecule^?1 s^?1): k₁ (OH + CH₂ = C(CH₃)CH₂Cl) = (3.23 ± 0.35) × 10^?11, k₂ (Cl + CH₂ = C(CH₃)CH₂Cl) = (2.10 ± 0.78) × 10^?10 with uncertainties representing ± 2σ. Product identification under atmospheric conditions was performed by solid phase microextraction/GC‐MS for OH reaction. Chloropropanone was identified as the main degradation product in accordance with the decomposition of the 1,2‐hydroxy alcoxy radical formed. Additionally, reactivity trends and atmospheric implications are discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Exploration on laminar flame propagation of 3,3-dimethyl-1-butene, 2,3-dimethyl-1-butene and 2,3-dimethyl-2-butene

Laminar flame propagation of branched hexene isomers/air mixtures including 3,3-dimethyl-1-butene (NEC₆D3), 2,3-dimethyl-1-butene (XC₆D1) and 2,3-dimethyl-2-butene (XC₆D2) was investigated using a high-pressure constant-volume cylindrical combustion vessel at 1–10 atm, 373 K and equivalence ratios of 0.7–1.5. The measured laminar burning velocity (LBV) decreases in the order of NEC₆D3, XC₆D1 and XC₆D2, which indicates distinct fuel molecular structure effects. A kinetic model was constructed and examined using the new experimental data. Modeling analyses were performed to reveal fuel-specific flame chemistry of branched hexene isomers. In the NEC₆D3 and XC₆D1 flames, the allylic CC bond dissociation reaction plays the most crucial role in fuel decomposition under rich conditions, while its dominance is replaced by H-abstraction reactions under lean conditions. The H-abstraction and H-assisted isomerization reactions are concluded to govern fuel consumption in the XC₆D2 flame under all investigated conditions. Both C₀C₃ reactions and fuel-specific reactions are found to be influential to the laminar flame propagation of the three branched hexene isomers. Fuel molecular structure effects were analyzed with special attentions on key intermediates distributions and fuel-specific reactions in all flames. Due to the formation selectivity of key intermediates such as 2-methyl-1,3-butadiene and 2,3-dimethyl-1,3-butadiene, the production of reactive radicals especially H follows the order of NEC₆D3 > XC₆D1 > XC₆D2, which results in the same order of fuel reactivities and LBVs.     

Stable silicon‐centered localized singlet 1,3‐diradicals XSi(GeY2)2SiX: theoretical predictions

Some localized singlet 1,3‐σ‐diradicals, XSi(GeY₂)₂SiX, (X = H, CH₃, SiH₃, C(CH₃)₃, NH₂ for X = F; Y = H, CH₃, OH, NH₂, SiH₃ for X = H) are theoretically designed by the orbital phase theory, the density functional theory (DFT) calculations , the second order Møller–Plesset perturbation theory (MP2), and the complete active space self‐consistent field (CASSCF) methods. The silicon‐centered singlet diradicals are more stable than the lowest triplets and than the bicylic σ‐bonded isomers if the isomers exist. The most stable singlet diradicals are not the π‐type diradicals, but the σ‐type diradicals where the radicals interact with each other through the Si? Ge bonds in the four‐membered rings. Copyright © 2007 John Wiley & Sons, Ltd.     

Reversible photomagnetism in a cobalt layered compound coupled with photochromic diarylethene

Photomagnetism is one of the most attractive topics in recent research on molecular solids. In order to produce a photo-controllable magnet, we have synthesized a novel organic-inorganic hybrid system coupled with a photochromic diarylethene anion, 2,2′-dimethyl-3,3′-(perfluorocyclopentene-1,2-diyl)bis(benzo[b]thiophene-6-sulfonate) (1a) and cobalt LDHs (layered double hydroxides). Based on the elemental analysis, the title compound, which was synthesized by the anion exchange reaction between Co₂(OH)₃(CH₃COO)·H₂O (2) and 1a, has the chemical composition, Co₄(OH)₇(1a)_0.5·3H₂O (3). Powder X-ray diffraction analysis revealed the interlayer distance of c=27.8 Å. The magnetic susceptibility measurements elucidated the ferromagnetic intra- and inter-layer interactions and the Curie temperature of T_c=9 K. By UV irradiation of 313 nm, 3 shows the photo-isomerization of diarylethene anion from the open form to the closed one in solid state, which leads to the decreases in the coercive field and the remnant magnetization. Furthermore, the photo-excited state is returned to the initial state (open form) almost reversibly by visible irradiation of 550 nm.     

Mechanism for sonochemical reduction of Au(III) in aqueous butanol solution under Ar based on the analysis of gaseous and water-soluble products

When an aqueous Au(III) solution containing 1-butanol was sonicated under Ar, Au(III) was reduced to Au(0) to form Au particles. This is because various reducing species are formed during sonication, but the reactivity of these species has not yet been evaluated in detail. Therefore, in this study, we analyzed the effects of Au(III) on the rates of the formation of gaseous and water-soluble compounds (CH₄, C₂H₆, C₂H₄, C₂H₂, CO, CO₂, H₂, H₂O₂, and aldehydes), and the rate of Au(III) reduction as a function of 1-butanol concentration. The following facts were recognized: 1) for Au(III) reduction, the contribution of the radicals formed by the pyrolysis of 1-butanol was higher than that of the secondary radicals formed by the abstraction reactions of 1-butanol with ·OH, 2) ·CH₃ and CO acted as reductants, 3) the contribution of ·H to Au(III) reduction was small in the presence of 1-butanol, 4) aldehydes and H₂ did not act as reductants, and 5) the types of species that reduced Au(III) changed with 1-butanol concentration.     

Synthesis and spectroscopic and electrochemical properties of binuclear complexes of Au(III) bridged by 6,7-dimethyl-2,3-di(2-pyridyl) quinoxaline

A method of synthesis of new diimine complexes of Au(III) with a four-dentate bridging ligand 6,7-dimethyl-2,3-di(2-pyridyl) quinoxaline (Ddpq), [Au₂(μ-Ddpq)Cl₄]Cl₂ and [(AuN^N)₂(μ-Ddpq)](NO₃)₆, where N^N is ethylenediamine, 2,2′-bipyridyl, or 1,10-phenanthroline, is described and the composition, structure, and properties of these complexes are studied. The coordination-induced chemical shifts in the ¹H NMR spectra are determined, as well as the spectral-luminescent and electrochemical parameters of the complexes. The nature of the energetically lowest spin-allowed ¹(π-d*)-and spin-forbidden ³(π-π*) states is established.     

Quantum chemical studies of the OH-initiated oxidation reactions of propenols in the presence of O2

ABSTRACT

The atmospheric oxidation mechanisms of 1- and 2-propenol initiated by OH radical have been theoretically investigated at the CCSD(T)//BH&;HLYP/6-311?+?+G(d,p) level of theory. Conventional transition state theory was employed to predict the rate constants for the initial reaction channels. The calculations clearly indicate that OH-addition channels contribute maximum to the total reaction, both for 1- and 2-propenol, while H-abstraction channels can be neglected at the temperature range of 220–520?K. The calculated total rate constants at 298?K are 1.66?×?10^?11 and 7.69?×?10^?12 cm³?molecule^?1?s^?1 respectively for 1- and 2-propenol, which are in reasonable agreement with the experimental values of similar systems (vinyl ethers?+?OH reactions). The deduced Arrhenius expressions are k(OH?+?1-propenol)?=?1.43?×?10^?12 exp[(743.7?K)/T] and k(OH?+?2-propenol)?=?2.86?×?10^?12 exp[(310.5?K)/T] cm³?molecule^?1?s^?1. Under atmospheric condition, the OH-addition intermediates (CH₃C?HCH(OH)₂, CH₃CH(OH)C?H(OH), CH₃CH(OH)₂?CH₂, CH₃?C(OH)CH₂(OH)) are likely to react rapidly with O₂, the theoretically identified major products for 1-propenol are HCOOH, CH₃CHO and CH₃CH(OH)CHO, and the dominant products for 2-propenol are CH₃COOH, HCHO and CH₃COCH₂OH, both companied with the regeneration of OH and HO₂ radicals (crucial reactive radicals in the atmosphere).     

X-ray investigation of dialkyldimethylammonium bromides

Abstract

A Series of dialkyldimethylammonium bromides (DDAB), (C _n H_2n+1)zN⁺(CH₃)₂Br^?with n = 10, 12, 14, 16 and 18 were investigated using X-ray diffraction. Measurements were performed by the photographic Guinier method as well as by diffractometer on samples aligned on a glass substrate. For a sample with n=12, X-ray high-pressure measurements were also performed which allowed us to confirm the destabilization under pressure of the phase existing on heating above the first transition point. For all the studied compounds, except for that with n =16, strong hysteresis and rich polymorphism were observed. A smectic T phase - high-temperature liquid crystal was confirmed for compounds with n= 16 and 18. All the remaining alkylammonⁱum salts have smectic an E high-temperature liquid crystal phase.     

Substituent effect on electron affinity,gas‐phase basicity,and structure of monosubstituted propargyl radicals and their anions: a theoretical study

The substituent effect of electron‐withdrawing groups on electron affinity and gas‐phase basicity has been investigated for substituted propargyl radicals and their corresponding anions. It is shown that when a hydrogen of the α‐CH₂ group or acetylenic CH in the propargyl system is substituted by an electron‐withdrawing substituent, electron affinity increases, whereas gas‐phase basicity decreases. The calculated electron affinities are 0.95 eV (CH?C? CH₂?), 1.15 eV (CH?C? CHF?), 1.38 eV (CH?C? CHCl?), 1.48 eV (CH?C? CHBr?) for the isomers with terminal CH and 1.66 eV (CF?C? CH₂?), 1.70 eV (CCl?C? CH₂?), 1.86 eV (CBr?C? CH₂?) for the isomers with terminal CX at B3LYP level. The calculated gas‐phase basicities for their anions are 378.4 kcal/mol (CH?C? CH₂:^?), 371.6 kcal/mol (CH?C? CHF:^?), 365.1 kcal/mol (CH?C? CHCl:^?), 363.5 kcal/mol (CH?C? CHBr:^?) for the isomers with terminal CH and 362.6 kcal/mol (CF?C? CH₂:^?), 360.4 kcal/mol (CCl?C? CH₂:^?), 356.3 kcal/mol (CBr?C? CH₂:^?) for the isomers with terminal CX at B3LYP level. It is concluded that the larger the magnitude of electron‐withdrawing, the greater is the electron affinity of radical and the smaller is the gas‐phase basicity of its anion. This tendency of the electron affinities and gas‐phase bacisities is greater in isomers with the terminal CX than isomers with the terminal CH. Copyright © 2009 John Wiley & Sons, Ltd.     

Specific features of phase transitions in molecular crystals of diols

A comparative analysis of the phase transitions in molecular crystals of diols with different chain lengths [1,15-pentadecanediol (CH₂)₁₄(OH)₂ and 1,16-hexadecanediol (CH₂)₁₅(OH)₂] has been performed using differential scanning calorimetry. A quantitative analysis of the temperature dependence of the heat capacity within the theory of diffuse (Λ-shaped) first-order phase transitions and the use of the temperature hysteresis have revealed a number of new effects associated with the specific features of the phase transitions in molecular crystals of diols.     

Use of a Lanthanide Shift Reagent for Simplified NMR Analysis of Borneol—Isoborneol Mixtures. Apparent Catalysis of OH Proton Exchange by LSR

The use of ¹H NMR at low field (60 MHz spectrometer frequency) for direct analysis of mixtures of borneol, 1, and isoborneol, 2, is considerably simplified by addition of the lanthanide shift reagent (LSR), tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium(III), 3. The effect of added 3 is twofold. Firstly, the analytical marker signals of the methine proton CHOH in 1 and 2, which are partly overlapped at 60 MHz in CDCl₃ (28°), are separated and rendered baseline-resolved due to preferential LSR binding to the less hindered endo OH of 1. Secondly, the absorption signals of the CHOH methines actually sharpen in the presence of 3, and display clearly defined multiplet structure, attributed to full exchange decoupling of the vicinal OH as a result of enhanced OH exchange rates when LSR is present.     

Substituent effects on gas-phase acidities of formic acid and its silicon and sulphur derivatives R − M(= X)XH(M = C., Si; X = O,S; R = H,F, CI,OH, NH2 and CH3)

Ab initio molecular orbital methods at the CBS-Q level of theory have been used to study the effect of substituent (F, Cl, NH₂, OH and CH₃) on the gas-phase acidities of formic acid, HCOOH, its silicon and sulphur derivatives R-M(= X)XH(M = C., Si; X = 0, S; R = F, Cl, OH, NH₂ and CH₃). For formic acid and its thio and dithio derivatives the acidity changes upon substitution are irregular and depend on both the type of substituent, position and degree of replacement of oxygen atoms by sulphur atoms. For sila carboxylic acids and their thio and dithio derivatives the calculated acidities regularly increase in the order: R-SiOOH < R-Si(=S)OH ? R-Si(=O)SH < R-SiSSH(R = H, F, Cl, OH, NH₂ and CH₃). The chloro derivatives are the strongest among the acids studied. The highest gas phase acidity (1277.6 kJmol^?1) has been calculated for ClC(=S)OH.     

Synchrotron photoionization measurements of fundamental autoignition reactions: Product formation in low-temperature isobutane oxidation

Product formation in laser-photolytic Cl-initiated low-temperature (550–700 K) oxidation of isobutane in a slow-flow reactor was investigated by tunable synchrotron photoionization mass spectrometry. These experiments probed the time-resolved formation of products following photolytic initiation of the oxidation, and identify isomeric species by their photoionization spectra. The relative yields of oxygenated product isomers (2,2-dimethyloxirane, methylpropanal, and 3-methyloxetane) are in reasonable concord with measurements from Walker and co-workers (J. Chem. Soc. Faraday Trans. 74 (1) (1978) 2229–2251) at higher temperature. Oxidation of isotopically labeled isobutane, (CH₃)₃CD, suggests that methylpropanal formation can proceed from both (CH₃)₂CCH₂OOH and CH₃CH(CH₂)CH₂OOH isomers. Bimodal time behavior is observed for product formation; the initial prompt formation reflects “formally direct” channels, principally chemical activation, and the longer-timescale “delayed” component arises from dissociation of thermalized ROO and QOOH radicals. The proportion of prompt to delayed signal is smaller for the oxygenated products than for the isobutene product. This channel-specific behavior can be qualitatively understood by considering the different energetic distributions of ROO and QOOH in formally direct vs. thermal channels and the fact that the transition states involved in the formation of oxygenated products are “tighter” than that for isobutene formation.     

Two-dimensional condensation of water and alcohols on NaF

On the surface of NaF the adsorption isotherms of H₂O, D₂O, CH₃OH, C₃H₃OH and 1-C₃H₇OH as well as the infrared spectra of H₃O, D₂O, dilute HDO, CH₃OH and CH₃OD were measured. The adsorption temperatures of H₃O (253–308 K) were within the phase transition region where two phases of low and high density coexist, while those of CH₃OH, C₂H₅OH and 1-C₃H₃OH were yet within a super-critical region. The entropy of the 2D condensed H₂O on NaF was found to be 14.0 cal K^?1 mol^?1, which suggests that the condensed phase of water on NaF is liquid-like. The OD stretching band of dilute HDO in the 2D condensed water gives a maximum adsorption at ca. 2530 cm^?1 with a half width of ca. 150 cm^?1, being in good agreement with that in liquid water. Comparison of the integrated absorbance of the D₂O bending mode with that of the OD stretching mode suggests that the cluster size of the 2D condensed water on NaF decreases with increasing temperature. The 2D critical temperature and the occupied areas of these adsorbates enable us to conclude that the compatibility of the molecular size with the surface lattice is not important in the occurrence of the 2D condensation of the hydrogen-bonding molecules on NaF and that adsorbed molecules are randomly oriented on the surface to the extent similar to that in 3D liquid state.     

Quantum chemical study of the (Z)-2-penten-1-ol (HOCH2–CH = CHCH2CH3) + OH + O2 reactions

ABSTRACT

The mechanism and products of the reaction of (Z)-2-penten-1-ol [(Z)-PO21] with OH radical in the presence of O₂ have been elucidated by using high-level quantum chemical methods CCSD(T)/6-311+G(d,p)//BH&;HLYP/6-311++G(d,p). The calculations clearly indicate that addition channels contribute maximum to the total reaction and H-abstraction channels can be neglected at temperatures of 220–500 K. The rate constant for the reaction of OH radical with (Z)-PO21 at 298 K is computed to be 1.22 × 10^?10 cm³ molecule^?1 s^?1, which is in stronger agreement with the previously reported experimental values. The kinetic data obtained over the temperature range 220?500 K are used to derive an non-Arrhenius expression: k = 3.69 × 10^?13 × exp(1763.7/T) cm³ molecule^?1 s^?1. For the reaction of (Z)-PO21with OH radical in the presence of O₂, the major primary reaction products found in this study are propanal [CH₃CH₂C(O)H] and glycolaldehyde [HOCH₂C(O)H], whereas formaldehyde [HC(O)H], 2-hydroxybutanal [CH₃CH₂CH(OH)C(O)H] and the epoxide P18 are anticipated to be minor products. The calculated results are consistent with the recent experimental observations.     

A DFT study on the formation of CH3O on Cu2O(1 1 1) surface by CH3OH decomposition in the absence or presence of oxygen

The formation mechanism of CH₃O by the adsorption and decomposition of CH₃OH on clean and oxygen-precovered Cu₂O(1 1 1) surface has been investigated with density functional theory method together with the periodic slab models. Two possible formation pathways of CH₃O by CH₃OH decomposition on oxygen-precovered (O_pre) Cu₂O(1 1 1) surface were proposed and discussed. One is the O-H bond-cleavage of CH₃OH with H migration to O_pre to form CH₃O; the other is the C-O bond-scission of CH₃OH with CH₃ migration to O_pre leading to CH₃O_pre. The calculated results show that the O-H bond-breaking path has the lowest activation barrier 26.8 kJ mol⁻¹, the presence of oxygen-precovered on Cu₂O(1 1 1) surface exhibits a high surface reactivity toward the formation of CH₃O by the O-H bond-cleavage of CH₃OH, and reduce the activation barrier of O-H bond-cleavage. The C-O bond-breaking path was inhibited by dynamics, suggesting that the O atom of CH₃O is not from the oxygen-precovered, but comes from the O of CH₃OH. Meanwhile, the calculated results give a clear illustration about the formation mechanism of CH₃O in the presence of oxygen and the role of oxygen at the microscopic level.     

季戊四醇双缩苯乙二酮异构体的NMR研究

合成并利用¹H NMR表征了3,3′-二甲基-3,3′-二苯基-2,2′,4,4′-四氧杂螺[5, 5]十一烷（简称季戊四醇双缩苯乙二酮）,用Gaussian03软件中B3LYP/6-311+g*对化合物进行势能扫描,得到4种稳定结构. 用B3LYP/6-311++g**方法预测季戊四醇双缩苯乙二酮异构体的氢化学位移,得到的最稳态结构的氢化学位移与实验值偏差较小,并用CHK文件生成了异构体电子云密度等高线图,其电子云密度图说明静电屏蔽作用与氢质子化学位移的变化一致.     

Hydration-induced conformational changes in protonated 2,4-pentanedione in the gas phase

Starting with H⁺[CH₃C(O)CH₂C(O)CH₃] (denoted H⁺PD), the protonated diketone-water clusters H⁺PD(H₂O) _n (n = 1–3) have been characterized by density functional theory calculations in combination with vibrational predissociation spectroscopy to explore the conformational changes of a protonated bifunctional ion solvated by water in the gas phase. Theoretical calculations for H⁺PD revealed that the ion contains an intramolecular hydrogen bond (IHB), with two oxygen atoms bridged by the extra proton in an O—H⁺ … O form. Attachment of one water molecule to it readily ruptures this IHB, replacing the H⁺ by the H₃O⁺ moiety. Further replacement of the IHB by two water molecules occurs at n = 2 and the ?C(O)CH₂C(O)- chain is fully opened (or unfolded) after transfer of the extra proton to the water trimer at n = 3. To verify the computational findings, infrared spectroscopic measurements were performed using a vibrational predissociation ion trap spectrometer to identify cluster isomers from the signatures of hydrogen bonded and non-hydrogen bonded OH stretching spectra of H⁺PD(H₂O)_2,3 produced in a corona discharge supersonic expansion. Besides open form isomers, evidence for the formation of water-bridged structures has been found for H⁺PD(H₂O)₃ at an estimated temperature of 200 K. A detailed illustration of the unfolding steps as well as the energy profiles for the evolution of a two-water bridge isomer from the protonated H⁺PD monomer are analysed pictorially (including both stable intermediates and transition states) in the present investigation.