A comprehensive study of (CH3)2CHOC(S)SC(O)OCH3 using matrix isolation technique,X‐ray analysis,spectroscopic studies and theoretical calculations

Potassium isopropyl xanthate, (CH₃)₂CHOC(S)SK, reacts with methyl chloroformiate ClC(O)OCH₃ to yield (methoxycarbonyl) (2‐propoxythiocarbonyl) sulfide, (CH₃)₂CHOC(S)SC(O)OCH₃. This novel xanthogen formate was characterized by ¹H and ¹³C{¹H} NMR spectroscopy, mass spectrometry and IR and Raman spectroscopy. The structure of a single crystal of (CH₃)₂CHOC(S)SC(O)OCH₃ was determined by X‐ray diffraction analysis at 173 K. The conformational properties have been studied by liquid IR and Raman spectroscopy, matrix isolation spectroscopy together with photochemical studies and quantum chemical calculations (HF and B3LYP methods with the 6‐31+G* basis set). The analysis of the IR spectrum of liquid (CH₃)₂CHOC(S)SC(O)OCH₃ suggests the presence of two conformers in equilibrium at room temperature. However, in the photochemical matrix study, an equilibrium of three conformers was detected. These forms were further characterized by theoretical calculations. Different photolysis products, such as CH₃OC(O)SCH(CH₃)₂, OCS, CO, CO₂ and CS₂, were identified by matrix spectroscopy. The IR absorptions of CH₃OC(O)SCH(CH₃)₂, for which literature data are scarce, were analysed in the light of the results of appropriate theoretical calculations. Copyright © 2009 John Wiley & Sons, Ltd.     

Direct synthesis and characterization of highly ordered functional mesoporous silica thin films with high amino-groups content

A series of continuous, crack-free, highly ordered amino-functionalized mesoporous silica thin films have been directly synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of cationic CH₃(CH₂)₁₅N⁺(CH₃)₃Br⁻ (CTAB), nonionic C₁₆H₃₃(OCH₂CH₂)₁₀OH (Brij-56) or triblock copolymer H(OCH₂CH₂)₂₀(OCH(CH₃)CH₂)₇₀(OCH₂CH₂)₂₀)OH (P123) surfactant species under acidic conditions by sol-gel dip-coating. The molar ration of APTES/(TEOS + APTES) in the starting sol attains a value of 0.4. The effect of the sol aging on the mesostructure of thin films is systematically studied, and the optimal sol aging time is obtained for different surfactant systems. The amino-functionalized mesoporous silica thin films exhibit long-range ordering of 2D hexagonal (p6mm) and 3D cubic (Fm3m) pore arrays of size range from 2.2 to 8.3 nm following surfactants extraction as demonstrated by XRD, TEM and physical adsorption techniques. Based on BET surface area and weight loss, the surface coverage of amino-groups for thin films prepared using different surfactants is calculated to be 3.2 and above amino-groups per nm², which is very useful and promising for incorporating inorganic ions and biomolecules into these mesoporous silica materials.     

Speeds of sound and isentropic compressibilities of (2-ethoxyethanol + ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol) binary mixtures at 298.15 K

The speed of sound (u) has been obtained at a frequency of 8.3 MHz in {CH₃CH₂OCH₂CH₂OH + HOCH₂CH₂(OCH₂CH₂)_nOH}for n = 0, 1, 2, and 3 over the whole composition range of studied binary liquid mixtures, at T = 298.15 K. The speed of sound values were combined with those of our previous results for densities and viscosities to obtain isentropic compressibility (κ_s), free volume (V_f), and intermolecular free length (L_f). From all these data excess isentropic compressibility (κ_s^E), excess free volume (V_f^E) and excess intermolecular free length (L_f^E) as well as the deviations of the speed of sound (Δu) were obtained. The results are interpreted in terms of molecular interactions occurring in the solutions.     

Influence of boron concentration on growth characteristic and electro-catalytic performance of boron-doped diamond electrodes prepared by direct current plasma chemical vapor deposition

A series of boron-doped diamond (BDD) electrodes were prepared by direct current plasma chemical vapor deposition (DC-PCVD) with different compositions of CH₄/H₂/B(OCH₃)₃ gas mixture. A maximum growth rate of 0.65 mg cm⁻² h⁻¹ was obtained with CH₄/H₂/B(OCH₃)₃ radio of 4/190/10 and this growth condition was also a turning point for discharge plasma stability which arose from the addition of B(OCH₃)₃ that changed electron energy distribution and influenced the plasma reaction. The surface coating structure and electro-catalytic performance of the BDD electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Hall test, and electrochemical measurement and electro-catalytic oxidation in phenol solution. It is suggested that the boron doping level and the thermal stress in the films are the main factors affecting the electro-catalytic characteristics of the electrodes. Low boron doping level with CH₄/H₂/B(OCH₃)₃ ratio of 4/199/1 decreased the films electrical conductivity and its electro-catalytic activity. When the carrier concentration in the films reached around 10²⁰ cm⁻³ with CH₄/H₂/B(OCH₃)₃ ratio over a range of 4/195/5-4/185/15, the thermal stress in the films was the key reason that influenced the electro-catalytic activity of the electrodes for its effect on diamond lattice expansion. Therefore, the BDD electrode with modest CH₄/H₂/B(OCH₃)₃ ratio of 4/190/10 possessed the best phenol removal efficiency.     

Comparative study of electronic structure and optical properties of a series of Pt(II) complexes containing different electron‐donating and ‐withdrawing groups: a DFT study

We report a quantum‐chemistry study of electronic structures and spectral properties of a series of Pt(II) complexes containing different substituents (? CH₃ ( 1 ), ? OCH₃ ( 2 ), ? NO₂ ( 3 ), ? CF₃ ( 4 ), and ? COOH ( 5 )). 1 and 2 have been previously synthesized in experiment, while 3 – 5 are artificial complexes that we suggest can be used to investigate the electron‐withdrawing effect on charge injection, transport, absorption, and phosphorescence properties. The results reveal that the stronger electron‐donating and ‐withdrawing groups show stronger absorption intensity, while the phosphorescence efficiency is generally higher for complexes containing electron‐donating substituents. 1 and 2 are easier for hole injection, while 3 – 5 are easier for electron injection. The enhanced electron injection abilities of 3 – 5 will confine more excitons in the light‐emitting layer (EML) and may not result in lower electroluminescence (EL) efficiency than 1 and 2 . These results suggest that the three artificial complexes may be new emitters in organic light‐emitting diodes (OLEDs). Copyright © 2009 John Wiley & Sons, Ltd.     

Decomposition of alkanethiols adsorbed on Au (1 1 1) at low temperature

The adsorption and desorption of butanethiol (CH₃(CH₂)₃SH: C4), hexanethiol (CH₃(CH₂)₅SH: C6) and octanethiol (CH₃(CH₂)₇SH: C8) on Au (1 1 1) under vacuum condition have been studied by temperature programmed desorption (TPD). Desorptions of thiolate radical species were observed for C6 and C8. Connecting the desorption temperatures of parent thiols from the first layer and that of hydrogen, we were able to find a condition for thiolate radicals to be desorbed from the surface.     

Acid assisted proton transfer in 4‐[(4‐R‐phenylimino)methyl]pyridin‐3‐ols: NMR spectroscopy in solution and solid state,X‐ray and UV studies and DFT calculations

The behaviour of Schiff bases of 3‐hydroxy‐4‐pyridincarboxaldehyde and 4‐R‐anilines (R?H, CH₃, OCH₃, Br, Cl, NO₂) in acid media has been described. ¹H, ¹³C, ¹⁵N‐NMR chemical shifts allow to establish the protonation site and its influence on the hydroxyimino/oxoenamino tautomerism. DFT calculations, electronic spectra and X‐ray diffraction are in agreement with the NMR conclusions. Copyright © 2007 John Wiley & Sons, Ltd.     

Configuration dependence of photon stimulated ion desorption from methyl ester compounds induced by core excitation

Photon stimulated ion desorption (PSID) from methyl ester terminated self-assembled monolayer (MHDA-SAM, HS(CH₂)₁₅COOCH₃) and methyl mercaptoacetate (MA, HSCH₂COOCH₃) on Ag has been investigated using soft X-ray in the C and O K-edge regions. In MHDA-SAM on Ag, site-selective ion desorption has been clearly observed at resonant core excitations of C_1s, O_1s(OCH₃) → σ^∗(OCH₃) and O_1s(OCH₃) → σ^∗(COCH₃). Ion intensity in MA on Ag is obviously reduced for (n = 1-3) at C_1s, O_1s(OCH₃) → σ^∗(OCH₃) excitations, and no site-selective reaction at O_1s(OCH₃) → σ^∗(COCH₃) excitations has been observed. These reactions may be influenced by configurational difference of reactive sites. It is suggested that surface effects on the selective reaction due to positioning methyl ester group near the surface plays an important role.     

Single-pulse shock-tube study on the pyrolysis of small esters (ethyl and propyl propanoate,isopropyl acetate) and methyl isopropyl carbonate

Single-pulse shock-tube experiments were used to study the thermal decomposition of selected oxygenated hydrocarbons: Ethyl propanoate (C₂H₅OC(O)C₂H₅; EP), propyl propanoate (C₃H₇OC(O)C₂H₅; PP), isopropyl acetate ((CH₃)₂HCOC(O)CH₃; IPA), and methyl isopropyl carbonate ((CH₃)₂HCOC(O)OCH₃; MIC) The consumption of reactants and the formation of stable products such as C₂H₄ and C₃H₆ were measured with gas chromatography/mass spectrometry (GC/MS). Depending on the considered reactant, the temperatures range from 716–1102 K at pressures between 1.5 and 2.0 bar. Rate-coefficient data were obtained from first-order analysis. All reactants primarily decompose by six-center eliminations: EP → C₂H₄ + C₂H₅COOH (propionic acid); PP → C₃H₆ + C₂H₅COOH; IPA → C₃H₆ + CH₃COOH (acetic acid); MIC → C₃H₆ + CH₃OC(O)OH (methoxy formic acid). Experimental rate-coefficient data can be well represented by the following Arrhenius expressions: k(EP → products) = 10^13.49±0.16 exp(−214.95±3.25 kJ/mol/RT) s⁻¹; k(PP → products) = 10^12.21±0.16 exp(–191.21±2.79 kJ/mol/RT) s⁻¹; k(IPA → products) = 10^13.10±0.31 exp(–186.38±5.10 kJ/mol/RT) s⁻¹; k(MIC → products) = 10^12.43±0.29 exp(–165.25±4.46 kJ/mol/RT) s⁻¹. The determination of rate coefficients was based on the amount of C₂H₄ or C₃H₆ formed. The potential energy surface (PES) of the thermal decomposition of these four reactants was determined with the G4 composite method. A master-equation analysis was conducted based on energies and molecular properties from the G4 computations. The results indicate that the length of a linear alkyl substituent does not significantly influence the rate of six-center eliminations, whereas the change from a linear to a branched alkyl substituent results in a significant reactivity increase. The comparison between rate-coefficient data also shows that alkyl carbonates have higher reactivity towards decomposition by six-center elimination than esters. The results are discussed in in the context of reactivity patterns of carbonyl compounds.     

Computational design and screening of promising energetic materials: Novel azobis(tetrazoles) with ten catenated nitrogen atoms chain

Density functional theory methods were used to study on 2 N10 compounds, 1,1′‐azobis(tetrazole) and 1,1′‐azobis(5‐methyltetrazole). We systematically investigated 10 novel substituted azobis(tetrazoles) with 10 catenated nitrogen atoms and various energetic groups (–CF₃ 1 , –C(NO₂)₃ 3 , –N₃ 5 , –NH₂ 6 , –NHNH₂ 7 , –NHNO₂ 8 , –NO₂ 9 , –OCH₃ 10 , –OH 11 , –ONO₂ 12 ). The optimized geometry, frontier molecular orbitals, electrostatic potential, Infrared and nuclear magnetic resonance spectrum were calculated for inspecting the molecular structure and stability as well as chemical reactivity. The effects of different substituents on the density, enthalpy of formation, heat of explosion, detonation velocity and pressure, and sensitivity of the azobis(tetrazole) derivatives have been investigated. Compound 9 with nitro was found to have remarkable detonation performances (D = 9.61 km/s, P = 42.14 GPa), which are close to the excellent explosive CL‐20. Results show that compounds 1 , 3 , 4 , 7 , 9 , 11, and 12 have high potential to replace RDX. It is surprising that compounds 1 , 3 , 9, and 12 possess better energetic properties than HMX. These novel substituted azobis(tetrazoles) with unique N10 structure may be promising candidates of HEDMs with outstanding performance and acceptable sensitivities.     

Polymer electrolytes based on cross-linked cyclotriphosphazenes

Substituted cyclotriphosphazenes were used to prepare lithium ion conducting polymer networks. Two types of compounds were synthesized starting with the precursor hexachlorocyclotriphosphazene (HCCP): Type I (CVEEP) in which all the chlorine atoms in HCCP were replaced by vinyloxyethoxyethoxy groups (VEE = –OCH₂CH₂OCH₂CH₂OCHCH₂), and type II (CVMEEP) in which half of the chlorine was replaced by VEE and the other half by methoxyethoxyethoxy groups (MEE = –OCH₂CH₂OCH₂CH₂OCH₃). The terminal vinyl groups were used to build up a network by a thermally initiated cross-linking of lithium salt containing membranes. Polymer electrolytes with dissolved LiSO₃CF₃ and LiN(SO₂CF₃)₂ were investigated by impedance measurements. The ionic conductivity of CVMEEP with 10 wt.% LiSO₃CF₃ was 3.2 × 10^− 5 S/cm at 30 °C and 4.1 × 10^− 4 S/cm at 90 °C. Lower conductivity values in the range 10^− 8–10^− 9 S/cm were obtained at 30 °C for the highly crosslinked CVEEP. An interesting polymer electrolyte with good mechanical properties and a good conductivity of 1.3 × 10^− 5 S/cm (30 °C) was obtained from a solution of MEEP (= poly[bis(methoxy–ethoxy–ethoxy)phosphazene]) and LiSO₃CF₃ in CVEEP as an interpenetrating network.     

Hydroxyl end groups influence in vibrational and transport properties in polymer/monomer solutions: the PEO/EG case

A study has been made of vibrational properties in ethylene glycol (EG; H(OCH₂CH₂)OH) and EG monomethyl ether (EGmE; CH₃(OCH₂CH₂)OH) in solution together with poly(ethylene oxide) (PEO; H(OCH₂CH₂)_n,OH) at different concentrations, performed by Fourier transform infrared absorbance (FT-IR) spectroscopy. The results ae compared with previous viscometry and photon correlation spectroscopy (PCS) studies, using EG dimethyl ether (EGdE; CH₃(OCH₂CH₂)OCH₃) as solvent as well. These homologous systems differ from each other in the number of OH end groups, in particular two for EG, one for EgmE and zero for EGdE. Combining analysis of the vibrational and transport properties of EG, EGmE and EGdE in solution with PEO over a wide range of concentration made it possible to check the quality (good theta or poor) of these three different solvents and the role played by the hydrogen bond in the various solute-solvent interaction mechanisms, resulting in the well known de Gennes scaling law.     

The Influence on NMR Parameters of Silicon Penta Coordination in Silatranes

¹H, ¹³C, ¹⁹F and ²⁹Si NMR chemical shifts and coupling constants for Si-substituted silatranes, XSi(OCH₂CH₂)₃N, and triethoxysilanes, XSi(OCH₂CH₃)₃, where X = H, CH₃, and F have been studied. Expansion of the coordination numbers of silicon and tin leads to similar changes in the NMR parameters.     

Structural and thermochemical properties of methyl ethyl sulfide alcohols: HOCH2SCH2CH3, CH3SCH(OH)CH3, CH3SCH2CH2OH,and radicals corresponding to loss of H atom

Sulfide alkoxy radicals are important intermediates during the partial oxidation of alkyl sulfides in atmospheric chemistry and in combustion. The atmospheric reaction sequence to formation of the alkoxy radicals includes (1) initial reaction with OH to create a radical on a carbon site, (2) the carbon radical then associates with ³O₂ to form a peroxy radical, and (3) an NO radical reacts with the peroxy radical to form an alkoxy radical (RO?) plus NO₂. This study determines structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (Δ_fH°, S°, and C_p(T)) of 3 corresponding alcohols HOCH₂SCH₂CH₃, CH₃SCH(OH)CH₃, and CH₃SCH₂CH₂OH of methyl ethyl sulfides studied in order to characterize the thermochemistry of the respective alkoxy radicals. The lowest energy molecular structures were calculated using the B3LYP density functional level of theory with the 6‐311G(2d,d,p) basis set. Standard enthalpies of formation (Δ_fH°₂₉₈) for the radicals and their parent molecules were calculated using B3LYP/6‐31 + G(2d,p), CBS‐QB3, M062x/6‐311 + g(2d,p), and G3MP2B3 methods. Isodesmic reactions were used to determine ?_fH° values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31 + G(d,p) level theory. The contributions for S°₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by CBS‐QB3 calculations, with contributions from torsion frequencies replaced by internal rotor contributions. Group additivity and hydrogen bond increment values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxide molecules and their radicals.     

Thermochemistry,bond energies and internal rotor barriers of methyl sulfinic acid,methyl sulfinic acid ester and their radicals

Sulfur–Oxygen containing hydrocarbons are formed in oxidation of sulfides and thiols in the atmosphere, on aerosols and in combustion processes. Understanding their thermochemical properties is important to evaluate their formation and transformation paths. Structures, thermochemical properties, bond energies, and internal rotor potentials of methyl sulfinic acid CH₃S(?O)OH, its methyl ester CH₃S(?O)OCH₃ and radicals corresponding to loss of a hydrogen atom have been studied. Gas phase standard enthalpies of formation and bond energies were calculated using B3LYP/6‐311G (2d, p) individual and CBS‐QB3 composite methods employing work reactions to further improve accuracy of the ${\Delta} _{{\bf f}} H_{{\bf 298}}^{{\bf o}} $ . Molecular structures, vibration frequencies, and internal rotor potentials were calculated. Enthalpies of the parent molecules CH₃S(?O)OH and CH₃S(?O)OCH₃ are evaluated as ?77.4 and ?72.7 kcal mol^?1 at the CBS? QB3 level; Enthalpies of radicals C^?H₂? S(?O)? OH, CH₃? S^?(?O)₂, C^?H₂? S(?O)? OCH₃ and CH₃? S(?O)? OC^?H₂ (CBS‐QB3) are ?25.7, ?52.3, ?22.8, and ?26.8 kcal mol^?1, respectively. The CH₃C(?O)O—H bond dissociation energy is of 77.1 kcal mol^?1. Two of the intermediate radicals are unstable and rapidly dissociate. The CH₃S(?O)? O. radical obtained from the parent CH₃? S(?O)? OH dissociates into methyl radical (${\bf CH}_{{\bf 3}}^{{\bf .}} $ ) plus SO₂ with endothermicity (ΔH_rxn) of only 16.2 kcal mol^?1. The CH₃? S(?O)? OC^?H₂ radical dissociates into CH₃? S^?=O and CH₂=O with little or no barrier and an exothermicity of ?19.9 kcal mol^?1. DFT and the Complete Basis Set‐QB3 enthalpy values are in close agreement; this accord is attributed to use of isodesmic work reactions for the analysis and suggests this combination of B3LYP/work reaction approach is acceptable for larger molecules. Copyright © 2010 John Wiley & Sons, Ltd.     

Structure,thermal properties,conductivity and electrochemical stability of di-urethanesil hybrids doped with LiCF<Subscript>3</Subscript>SO<Subscript>3</Subscript>

Variable chain length di-urethane cross-linked poly(oxyethylene) (POE)/siloxane hybrid networks were prepared by application of a sol-gel strategy. These materials, designated as di-urethanesils (represented as d-Ut(Y′), where Y′ indicates the average molecular weight of the polymer segment), were doped with lithium triflate (LiCF₃SO₃). The two host hybrid matrices used, d-Ut(300) and d-Ut(600), incorporate POE chains with approximately 6 and 13 (OCH₂CH₂) repeat units, respectively. All the samples studied, with compositions ∞ > n ≥ 1 (where n is the molar ratio of (OCH₂CH₂) repeat units per Li⁺), are entirely amorphous. The di-urethanesils are thermally stable up to at least 200 °C. At room temperature the conductivity maxima of the d-Ut(300)- and d-Ut(600)-based di-urethanesil families are located at n = 1 (approximately 2.0 × 10⁻⁶ and 7.4 × 10⁻⁵ Scm⁻¹, respectively). At about 100 °C, both these samples also exhibit the highest conductivity of the two electrolyte systems (approximately 1.6 × 10⁻⁴ and 1.0 × 10⁻³ Scm⁻¹, respectively). The d-Ut(600)-based xerogel with n = 1 displays excellent redox stability.     

Structures and thermochemistry of methyl ethyl sulfide and its hydroperoxides: HOOCH2SCH2CH3, CH3SCH(OOH)CH3, CH3SCH2CH2OOH,and radicals

Hydroperoxides and the corresponding peroxy radicals are important intermediates during the partial oxidation of methyl ethyl sulfide (CH₃SCH₂CH₃) in both atmospheric chemistry and in combustion. Structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (ΔH_f^o, S^o and C_p(T)) of 3 corresponding hydroperoxides CH₂(OOH)SCH₂CH₃, CH₃SCH(OOH)CH₃, CH₃SCH₂CH₂OOH of methyl ethyl sulfides, and the radicals formed via loss of a hydrogen atom are important to understanding the oxidation reactions of MES. The lowest energy molecular structures were identified using the density functional B3LYP/6‐311G(2d,d,p) level of theory. Standard enthalpies of formation (ΔH_f^o₂₉₈) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods. Isodesmic reactions were used to determine ?H_f^o values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31G(d,p) level theory. Contributions for S^o₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions. The recommended values for enthalpies of formation of the most stable conformers of CH₃SCH₂CH_2, CH₂(OOH)SCH₂CH₃, CH₃SCH(OOH)CH₃, and CH₃SCH₂CH₂OOH are ?14.0, ?33.0, ?37.2, and ?32.7 kcal/mol, respectively. Group additivity values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxides. Groups for use in group additivity estimation of sulfur peroxide thermochemical properties were developed.     

Steric effects on the mechanism of reaction of nucleophilic substitution of β‐substituted alkoxyvinyl trifluoromethyl ketones with four secondary amines

The kinetics of the reaction of β‐substituted β‐alkoxyvinyl trifluoromethyl ketones R¹O‐CR²?CH‐COCF₃ ( 1a – e ) [( 1a ), R¹?C₂H₅, R²?H; ( 1b ), R¹?R²?CH₃; ( 1c ), R¹?C₂H₅, R²?C₆H₅; ( 1d ), R¹?C₂H₅, R²?V^?pNO₂C₆H₄; ( 1e ), R¹?C₂H₅, R²?C(CH₃)₃] with four aliphatic amines ( 2a – d ) [( 2a ), (C₂H₅)₂NH; ( 2b ), (i‐C₃H₇)₂NH; ( 2c ), (CH₂)₅NH; ( 2d ), O(CH₂CH₂)₂NH] was studied in two aprotic solvents, hexane and acetonitrile. The least reactive stereoisomeric form of ( 1a – d ) was the most populated ( E‐s‐Z‐o‐Z ) form, whereas in ( 1e ), the more reactive form ( Z‐s‐Z‐o‐Z ) dominated. The reactions studied proceeded via common transition state formation whose decomposition occurred by ‘uncatalyzed’ and/or ‘catalyzed’ route. Shielding of the reaction centre by bulky β‐substituents lowered abruptly both k′ (‘uncatalyzed’ rate constant) and k″ (‘catalyzed’ rate constant) of this reaction. Bulky amines reduced k″ to a greater extent than k′ as a result of an additional steric retardation to the approach of the bulky amine to its ammonium ion in the transition state. An increase in the electron‐withdrawing ability of the β‐substituent increased ‘uncatalyzed’ k′ due to the acceleration of the initial nucleophile attack (k₁) and ‘uncatalyzed’ decomposition of transition state (k₂) via promoting electrophilic assistance (through transition state 8 ). The amine basicity determined the route of the reaction: the higher amine basicity, the higher k₃/k₂ ratio (a measure of the ‘catalyzed’ route contribution as compared to the ‘uncatalyzed’ process) was. ‘Uncatalyzed’ route predominated for all reactions; however in polar acetonitrile the contribution of the ‘catalyzed’ route was significant for amines with high pK_a and small bulk. Copyright © 2007 John Wiley & Sons, Ltd.     

Structural and thermochemical studies on CH3SCH2CHO,CH3CH2SCHO,CH3SC(═O)CH3, and radicals corresponding to loss of H atom

CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ are intermediates during the partial oxidation of CH₃SCH₂CH₃ in the atmosphere and in combustion processes. Thermochemical properties (ΔH_f^o, S^o and C_p(T)), structures, internal rotor potentials, and C─H bond dissociation energies of the parent molecules and their radicals formed after loss of a hydrogen atom are of value in understanding the oxidation processes of methyl ethyl sulfide. The lowest energy molecular structures were initially determined using the density functional B3LYP/6‐311G/(2d,d,p) level of theory. Standard enthalpies of formation (ΔH_f^o₂₉₈) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods using isodesmic reactions. Internal rotation potential energy diagrams and internal rotation barriers were investigated using B3LYP/6‐31 + G(d,p) level calculations. The contributions for S^o₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation on the basis of the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions from the method of Pitzer‐Gwinn. The recommended values for enthalpies of formation of the most stable conformers of CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ are ?34.6 ± 0.8, ?42.4 ± 1.2, and ‐49.7 ± 0.8 kcal/mol, respectively. The structural and thermochemical data presented for CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ and their radicals are of value in understanding the mechanism and kinetics of methyl ethyl sulfide oxidation under varied temperatures and pressures. Group additivity values are developed for estimating properties of structurally similar, larger sulfur‐containing compounds.     

Quantitative analysis of mixed self-assembled monolayers using ToF-SIMS

The spacing of chemical functional groups on self-assembled monolayers (SAMs) plays an important role in controlling the density of biomolecules in biochips and biosensors. In this sense, a mixed SAM made of two different terminal groups is a useful organic surface since spacing can be easily controlled by changing a relative mole fraction in a mixture solution. In this study, an acetylene-OCH₂O(EG)₃(CH₂)₁₁S-S(CH₂)₁₁(EG)₃OCH₂O-propene (Eneyne) SAM and mixed SAMs made by a mixture of (S(CH₂)₁₁(EG)₃OCH₂O-acetylene)₂ (Diyne) and (S(CH₂)₁₁(EG)₃OCH₂O-propene)₂ (Diene) were produced on gold substrates and measured by using ToF-SIMS. The secondary ion yield ratio of [Au·S(CH₂)₁₁(EG)₃OCH₂O-acetylene]⁻ to [Au·S(CH₂)₁₁(EG)₃OCH₂O-propene]⁻ was measured for each mixed SAM and plotted as a function of the mole fraction of Diyne to Diene in a SAM solution. The ion yield ratio of a mixed SAM produced from a solution with a mole fraction of 0.5 (i.e., 1:1 mixture) was 0.3, which corresponded well to the ion yield ratio measured from an Eneyne SAM. A time-dependent experiment of Eneyne SAM formation and immersion experiment of Eneyne SAM into Diyne solution or into Diene solution were performed. The relative ion yield ratio of 0.3 was due to a different secondary ion formation and not due to the difference in the amount of adsorbates on the surface, nor to the different binding strengths onto the gold surface. Our study shows that a mixed SAM with well-controlled spacing can be produced and quantified by using the ToF-SIMS technique.