Adsorption of Tri‐n‐Butyl Phosphate (TBP) from NaClO4 Aqueous Solution on Hg Electrode

The adsorption of TBP on Hg electrode from aqueous NaClO₄ media has been studied using differential capacity and chronocoulometric measurements. TBP adsorbs in two steps, the first corresponding to a flat and second to a perpendicular orientation. Both orientations were observed in the entire investigated potential range. The maximal measured surface concentration (Γ_max) of TBP reaches a value of 1.55×10^?10 mol cm^?2, which corresponds to the theoretical value for densely packed molecules in perpendicular orientation. Γ value of the first isotherm step plateau is about 7 to 15% smaller than Γ_max and decreases strongly at potentials more negative than ?0.9 V due to the repelling of negative charges between the electrode and the phosphate group. The standard Gibbs energy of adsorption was found to reach the value of ?34 kJ mol^?1.     

Matrixreaktion von GeO mit F2. IR-spektroskopischer nachweis von molekularem OGeF2

GeO reacts with F₂ in an argon matrix after photolysis with a high-pressure mercury lamp to form OGeF₂. Isotopic splitting (¹⁶O/¹⁸O and ⁷⁰Ge/⁷²Ge/⁷⁴Ge) and force constant calculations show that the fundamentals observed can be assigned to a planar molecule OGeF₂. The value of the force constant of the GeO double bond, 7.43 × 10² N m^?1, is as expected (GeO₂ 7.32 × 10² N m^?1), but the GeF bond is unexpectedly weak (f_GeF = 5.01 × 10² N m^?1).     

Theoretical evaluation of the nature and strength of the F������F intermolecular interactions present in fluorinated hydrocarbons

The nature, strength and directionality of C?CF···F interactions were theoretically evaluated on all symmetry unique dimers present in the CF₄, C₂F₄ and C₆F₆ crystals and on CF₄, CHF₃, CH₂F₂ and CH₃F model dimers placed in two different geometries. On each dimer, the interaction energy was computed at the MP2/aug-cc-pVDZ level, and also an Atoms in Molecule analysis of the dimer electron density was done to find all intermolecular bonds. The characterization was completed by computing the energy components of the dimer interaction energy, using the SAPT method. The results show that in most dimers found in the CF₄, C₂F₄ and C₆F₆ crystals, there are more than one C?CF···F intermolecular bond and sometimes even a C?CF···?? intermolecular bond. By selecting dimers presenting one C?CF···F bond, the following strength can be estimated for a single C?CF···F bond: ?0.21?kcal/mol in C(sp³) atoms, ?0.25?kcal/mol in C(non-aromatic sp²), ?0.41?kcal/mol in C(aromatic sp²). The interaction energy of the dimer grows almost linearly with the number of C?CF···F bonds present. The relative orientation of the C?CF···F bond affects the bond strength. The SAPT calculations indicate that in collinear dimers, C?CF···F interactions are strongly dominated by the dispersion energetic component, while when in non-collinear conformations the electrostatic component can be as important as the dispersion one.     

1H NMR spectra. Part 29§: proton chemical shifts and couplings in esters—the conformational analysis of methyl γ‐butyrolactones

The ¹H NMR spectra of 35 cyclic and acyclic esters are analysed to give the ¹H chemical shifts and couplings. The substituent chemical shifts of the ester group were analysed using three‐bond (γ) effects for near protons and the electric field, magnetic anisotropy and steric effect of the ester group for more distant protons. The electric field is calculated from the partial atomic charges on the O?C = O atoms, and the asymmetric magnetic anisotropy of the carbonyl group acts at the midpoint of the C = O bond. The values of the anisotropies Δχ_parl and Δχ_perp were for the aliphatic esters 10.35 and ?18.84 and for the conjugated esters 7.33 and ?15.75 (×10^?6 ų/molecule). The oxygen steric coefficients found were 104.4 (aliphatic C = O), 45.5 (aromatic C = O) and 16.0 (C–O) (×10^?6 Å⁶/molecule). After parameterisation, the overall RMS error for the data set of 280 entries was 0.079 ppm. The strongly coupled ¹H NMR spectra of the 2‐methyl, 3‐methyl and 4‐methyl γ‐butyrolactones were analysed and the methyl conformational equilibrium obtained from the observed couplings. The observed versus calculated density functional theory (DFT) ΔG(ax‐eq) was 1.0 (1.01), 0.34 (0.54) and 0.65 (0.71) kcal/mol res. The shielding effect of a methyl cis to a proton in the five‐membered lactone rings is ?0.40 ±0.05 ppm and deshielding trans effect 0.12 ±0.05 ppm, which is common to both five and six membered rings. The cis/trans isomerism in the vinyl esters methyl acrylate, crotonate and methacrylate and methyl furoate was examined using the ¹H chemical shifts. The calculated shifts of both the cis and trans isomers were in good agreement with the observed shifts. Copyright © 2012 John Wiley & Sons, Ltd.     

Stereoelectronic Aspects of the Anomeric Effect in Fluoromethylamine

High-level ab initio calculations have been made for fluoromethylamine to study structural and energetic effects of the relative orientation of the N lone pair to the C? F bond. The anti-conformer (N lone pair anti-planar to the C? F bond) corresponds to the global energy minimum. It has the longest C? F distance, the shortest C? N distance, and is 7.5 kcal·mol^?1 more stable than the related perpendicular conformation (lone pair perpendicular to the C? F bond). The syn-conformation also shows hallmarks of the anomeric effect: long C? F bond, short C? N bond, and energetic stability when allowance is made for the two pairs of eclipsed hydrogens. The transition state for N inversion is close to the syn-structure; rotation about the C? N bond is strongly coupled with this inversion process. Small bond distance changes of ca. 0.02 Å between parallel and perpendicular conformations are associated with dissociation energy differences of ca. 30 kcal·mol^?1. Various criteria for assessing the strength of the anomeric effect are discussed.     

Uniaxial Draw Of Poly(aryl-ether-ether-ketone) by solid-state extrusion

Poly(aryl-ether-ether-ketone) (PEEK) films and rods have been solid-state extruded at 154 and 310°C, respectively. The crystal orientation functions, melting behavior, density, and tensile properties of the drawn PEEK films (EDR ≤ 3.7) and rods (EDR ≤ 5.5) have been measured. As extrusion draw ratio (EDR) was increased, the c-axis orientation function, melting temperature, and tensile modulus and strength increased. Moduli up to 6.5 GPa and the strengths up to 600 MPa, 3 and 6 times the values of undrawn films, respectively, were obtained for the drawn films. The thermal expansivities along (α_‖) and perpendicular (α_?) to the draw direction of PEEK rods were measured from ?40 to +10°C. As EDR was increased, α_? increased, but α_‖ decreased. At EDRs of 3.8 and 5.5, α_‖ even exhibited negative values (about ?5 × 10^?6°C^?1), probably due to reversible contraction of elongated tie-molecules.     

After the electronic field: Structure,bonding, and the first hyperpolarizability of HArF

In this work, we add different strength of external electric field (E_ext) along molecule axis (Z‐axis) to investigate the electric field induced effect on HArF structure. The H‐Ar bond is the shortest at E_ext = ?189 × 10^?4 and the Ar‐F bond show shortest value at E_ext = 185 × 10^?4 au. Furthermore, the wiberg bond index analyses show that with the variation of HArF structure, the covalent bond H‐Ar shows downtrend (ranging from0.79 to 0.69) and ionic bond Ar‐F shows uptrend (ranging from 0.04 to 0.17). Interestingly, the natural bond orbital analyses show that the charges of F atom range from ?0.961 to ?0.771 and the charges of H atoms range from 0.402 to 0.246. Due to weakened charge transfer, the first hyperpolarizability (β_tot) can be modulated from 4078 to 1087 au. On the other hand, make our results more useful to experimentalists, the frequency‐dependent first hyperpolarizabilities were investigated by the coupled perturbed Hartree‐Fork method. We hope that this work may offer a new idea for application of noble‐gas hydrides. © 2013 Wiley Periodicals, Inc.     

Vibrational spectra and normal coordinate analysis of CF3 compounds : XXXIV. The bis(trifluoromethyl)difluoroborate anion: X-ray structure of Cs[(CF3)2BF2]

The ¹⁰B and ¹¹B IR and Raman spectra of the [(CF₃)₂BF₂]^? anion are reported, assigned, and used to determine a quadratic local symmetry force field via a normal coordinate analysis. The crystal structure of Cs[(CF₃)₂BF₂] (P2₁/m, a 5.958(1), b 7.628(1), c 8.2997(9) Å, β 100.50(1)°, Z = 2, d_c 2.863 g cm^?3 has been determined by X-ray diffractometry. The most important force constants are f(BC) 3.68 × 10², f(BF) 4.17 × 10² and f(CF) 4.85 × 10² N/m, the respective mean bond lenghts being 1.618, 1.391 and 1.353 Å. The FBF and CBC bond angles are 108.1(4) and 113.6(5)°, respectively. Apparently because of Cs?F(B, C) interactions, one BC bond has a staggered and the other an eclipsed conformation in the solid state.     

Matrixreaktion von SiO mit F2. IR-spektroskopischer nachweis von molekularem OSiF2

SiO reacts with F₂, in an argon matrix after photolysis with a high-pressure mercury lamp to form OSiF₂. Isotopic splitting (¹⁶O/¹⁸O and ²⁸Si/²⁹Si) and force constant calculations show that the 6 fundamentals observed can be assigned to the planar molecule OSiF₂. The value of the force constant of the SiO double bond, which was calculated as approximately 9 × 10² N m^?1 in earlier investigations, is confirmed by this work.     

Wasserstoffbrückenbindungen mit Cyanidionen? Die Strukturen von 1,3‐Diisopropyl‐4,5‐dimethylimidazoliumcyanid und 1‐Isopropyl‐3,4,5‐trimethylimidazoliumcyanid

Hydrogen Bonds with Cyanide Ions? The Structures of 1,3‐Diisopropyl‐4,5‐dimethylimidazolium Cyanide and 1‐Isopropyl‐3,4,5‐trimethylimidazolium Cyanide 1,3‐Diisopropyl‐4,5‐dimethylimidazolium cyanide ( 2a ) and 1‐isopropyl‐3,4,5‐trimethylimidazolium cyanide ( 2b ) are obtained from the reaction of the corresponding 2,3‐dihydrodimethylimidazol‐2‐ylidenes ( 1 ) and hydrogen cyanide in excellent yield. Their crystal structure analyses reveal the presence of ion pairs linked by hydrogen bonds. The crystal structure analysis of 2a reveals a near colinear orientation of the C(1)‐H bond axis and the cyanide ion while in 2b this orientation is perpendicular. In both cases, the interionic distances are in the expected range for hydrogen bonds. Ab‐initio calculations of the total energy of the salts 2 indicate small differences in energy between the colinear and perpendicular orientation of the ions as well as between the colinear C‐H···C‐N and C‐H···N‐C orientations. The comparison of calculated and measured ¹³C and ¹⁵N NMR chemical shifts does not allow the distinction between the possible orientations.     

Transition metal compatibilization of poly(vinylamine) and poly(ethylene imine)

Poly(vinylamine), PVA, complexes with cobalt chloride hexahydrate exhibit a 45 °C enhancement in the glass‐transition temperature per mol % of the d‐block metal cation. Poly(ethylene imine), PEI, complexes with CoCl₂(H₂O)₆ exhibit a 20 °C enhancement in T_g per mol % Co²⁺. Since the basicities of primary and secondary amines are comparable (i.e., pK_b,PVA ≈ 3.34 vs. pK_b,PEI ≈ 3.27) and the rates at which each polymeric ligand displaces waters of hydration in the coordination sphere of Co²⁺ are similar, transition metal compatibilization is operative in blends of both polymers with CoCl₂(H₂O)₆. These two polymers are immiscible in the absence of the inorganic component. Infrared spectroscopy suggests that nitrogen lone pairs in PVA and PEI coordinate to Co²⁺. The stress–strain response of a 75/25 blend of PVA and PEI with 2 mol % Co²⁺ reveals a decrease in elastic modulus from 4.4 × 10⁹ N/m² to 5.7 × 10⁷ N/m², a decrease in fracture stress from 3.7 × 10⁷ N/m² to 2.0 × 10⁶ N/m², and an increase in ultimate strain from 1.3 to 12% relative to the 75/25 immiscible polymer–polymer blend. A plausible explanation for this effect is based on the fact that cobalt chloride hexahydrate compatibilizes both polymers by forming a coordination bridge between nitrogen lone pairs in dissimilar chains. Hence, poly(ethylene imine), which is very weak with a T_g near −40 °C, is integrated into a homogeneous structure with poly(vinylamine) and the mechanical properties of the individual polymers are averaged in the compatibilized ternary complex. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 552–561, 2000     

Star poly(methyl methacrylate) with end‐functionalized arm chains by ruthenium‐catalyzed living radical polymerization

Star polymers with end‐functionalized arm chains (surface‐functionalized star polymers) were synthesized by the in situ linking reaction between ethylene glycol dimethacrylate (linking agent) and an α‐end‐functionalized linear living poly(methyl methacrylate) in RuCl₂(PPh₃)₃‐catalyzed living radical polymerization; the terminal on the surface functionalities included amides, alcohols, amines, and esters. The star polymers were obtained in high yields (75–90%) with initiating systems consisting of a functionalized 2‐chloro‐2‐phenylacetate or ‐acetamide [F? C(O)CHPhCl; F = nPrNH? , HOCH₂CH₂O? , Me₂NCH₂CH₂O? , or EtO? ; initiator] and n‐Bu₃N (additive). The yield was lower with a functionalized 2‐bromoisobutyrate [Me₂NCH₂CH₂OC(O)CMe₂Br] initiator or with Al(Oi‐Pr)₃ as an additive. Multi‐angle laser light scattering analysis showed that the star polymers had arm numbers of 10–100, radii of gyration of 6–23 nm, and weight‐average molecular weights of 1.3 × 10⁵ to 3.0 × 10⁶, which could be controlled by the molar ratio of the linking agent to the linear living polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1972–1982, 2002     

Long branching in poly(vinyl acetate) and poly(vinyl alcohol). III. Kinetic study of the branching reaction in the radical polymerization of vinyl acetate

The branching reaction in the radical polymerization of vinyl acetate was studied kinetically. Branching occurs by polymer transfer as well as terminal double-bond copolymerization. The chain-transfer constants to the main chain (C_p,2) and to the acetoxy methyl group (C_p,1) on the polymer were calculated on the basis of the experimental data described in the preceding paper giving C_p,2 = 3.03 × 10^?4, C_p,1 = 1.27 × 10^?4 at 60°C, and C_p,2 = 2.48 × 10^?4, C_p,1 = 0.52 × 10^?4 at 0°C. Chain transfer to monomer is important with respect to the formation of the terminal double bond. The total values of transfer constants to the α- or β-position in the vinyl group and the acetoxymethyl group in vinyl acetate was determined to be 2.15 × 10^?4 at 60°C. The transfer constant to the acetyl group in the monomer (C_m,1) was also evaluated to be 2.26 × 10^?4 at 60°C from the quantitative determination of the carboxyl terminals in PVA. These facts suggest that the chain-transfer constant to the α- or β-position in the monomer (C_m,2) is nearly equal to zero within experimental error. Copolymerization reactivity parameters of the terminal double bond were also estimated. In conclusion, it has become clear that the formation of nonhydrolyzable branching by the terminal double-bond reaction can be almost neglected, and hence that the long branching in PVA is formed only by the polymer transfer mechanism. On the other hand, a large number of hydrolyzable branches in PVAc are prepared by the terminal double-bond reaction rather than by polymer transfer.     

Mechanistic and kinetic study on the ozonolysis of 2,4-hexadienedial

The formation and unimolecular reactions of primary ozonides and carbonyl oxides arising from the O₃-initiated reactions of 2,4-hexadienedial (HDE) have been investigated using the density functional theory and ab initio method. The activation energies of O₃ cycloaddition to the >C=C< and >C=O bonds of HDE for the formation primary ozonides (POZ1 and POZ2) are 4.79 and 21.37 kcal mol^?1, respectively, implying that the initial O₃ to the >C=C< bond is favorable pathway. Cleavage of POZ1 to form carbonyl oxides occurs with a barrier of 12.19–21.35 kcal mol^?1, and the decomposition energies range from ?1.09 to ?15.75 kcal mol^?1. The CHOCHOO radical, the hydroxyl radical (OH) formation via H-migration is more favorable than the dioxirane formation via rearrangement. However, the CHOCH=CHCHOO radical, the dioxirane formation via rearrangement is more favorable than OH formation. Using the transition state theory, the rate constants of formation of POZ1 and POZ2 are 1.49 × 10^?19 and 6.03 × 10^?25 cm³ molecule^?1 s^?1 at 300 K, respectively. This study shows that the hyperconjugative effect makes O₃ addition to >C=C< and >C=O bonds of HDE more difficult than to >C=C< bond of ethylene and isoprene and to >C=O bond of formaldehyde. The largest rate constants of OH formation and dioxirane formation in the unimolecular reactions of carbonyl oxides are 6.13 × 10^?4 and 7.93 × 10^?1 s^?1 at 300 K, respectively. The dioxirane is main product in the unimolecular reaction of the carbonyl oxides arising from the O₃-initiated reaction of HDE.     

Theoretical Investigations on Fluorine-Substituted Ethylene Dications C2HnF4-n 2+(n = 0–4)

The optimized geometries and energies of fluorine-substituted ethylene dications C₂H_nF_4-n ²⁺ (n = 0–4) have been investigated by means of ab initio methods. At the MP3/6-31G**//6-31G* + zero-point energy level of theory, the results predict that C₂F₄²⁺ and C₂HF₃²⁺ are planar, while C₂H₄²⁺, C₂H₃F²⁺ and 1,1—C₂H₂F₂²⁺ prefer a perpendicular geometry. For 1,2—C₂H₂F₂²⁺ an energy difference of only 0.3 kcal/mol is found between the (trans) planar and perpendicular structure. The stabilizations attributed to hyperconjugation, fluorine lone-pair donation, and (C? F) double-bond conjugation are discussed. A comparison is made for the C? C and C? F stretching frequencies determined at 6-31G*//6-31G* between the neutral and dicationic species. The theoretically determined ionization energies for the vertical process N⁺ → N²⁺ at the MP3/6-31G*//3-21G level are compared with experimental Q_min values.     

Conformation of cationic N,N‐di­methyl­glycine in di­methyl­glycinium tri­fluoro­acetate

In the title compound, C₄H₁₀NO₂⁺·C₂F₃O₂^?, the main N—C—COOH skeleton of the protonated amino acid is nearly planar. The C=O/C—N and C=O/O—H bonds are syn and the two methyl groups are gauche to the methyl­ene H atoms. The conformation of the cation in the crystal is compared to that given by ab initio calculations (Hartree–Fock, self‐consistent field molecular‐orbital theory). The tri­fluoro­acetate anion has the typical staggered conformation with usual bond distances and angles. The cation and anion form dimers through a strong O—H?O hydrogen bond which are further interconnected in infinite zigzag chains running parallel to the a axis by N—H?O bonds. Weaker C—H?O interactions involving the methyl groups and the carboxy O atoms of the cation occur between the chains.     

Activity and stability spontaneously enhanced toward ethylene polymerization by employing 2‐(1‐(2,4‐dibenzhydrylnaphthylimino)ethyl)‐6‐(1‐(arylimino)ethyl) pyridyliron(II) dichlorides

A series of 2‐(1‐(2,4‐dibenzhydrylnaphthylimino)ethyl)‐6‐(1‐(arylimino)ethyl)pyridyliron(II) complexes ( Fe1 ? Fe5 ) was synthesized and characterized. The molecular structure of the representative Fe2 was determined by single‐crystal X‐ray diffraction, revealing a distorted pseudo‐square‐pyramidal geometry around the iron center. On activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all these iron complex precatalysts performed with high activities (up to 1.58 × 10⁷ g (PE) mol^?1 (Fe) h^?1) toward ethylene polymerization, producing highly linear polyethylenes with high molecular weight and bimodal distribution, which was in accordance with high temperature ¹³C NMR, high T _m values (T _m ～130 °C) and the GPC curves of the obtained polyethylenes. Meanwhile, DFT calculation results also showed the good correlation between net charges on iron and experimental activities. Compared with previous bis(imino)pyridyliron analogues, the current iron complexes containing the benzhydrylnaphthyl groups exhibited relatively higher activities and better thermal‐stability at elevated temperatures, especially at 80 °C as the industrial operating temperature, and still showed high activities toward ethylene polymerization up to 8.57 × 10⁶ g (PE) mol^?1 (Fe) h^?1 in the presence of co‐catalyst MMAO. In addition, these iron complex precatalysts all exhibited long lifetimes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 988–996     

Kinetics of hydroxyl radical reactions with formaldehyde and 1,3,5-trioxane between 290 and 600 K

Absolute rate constants are measured for the reactions: OH + CH₂O, over the temperature range 296–576 K and for OH + 1,3,5-trioxane over the range 292–597 K. The technique employed is laser photolysis of H₂O₂ or HNO₃ to produce OH, and laser-induced fluorescence to directly monitor the relative OH concentration. The results fit the following Arrhenius equations: k (CH₂O) = (1.66 ± 0.20) × 10^?11 exp[?(170 ± 80)/RT] cm³ s^?1 and k(1,3,5-trioxane) = (1.36 ± 0.20) × 10^?11 exp[?(460 ± 100)/RT] cm³ s^?1. The transition-state theory is employed to model the OH + CH₂O reaction and extrapolate into the combustion regime. The calculated result covering 300 to 2500 K can be represented by the equation: k(CH₂O) = 1.2 × 10^?18 T^2.46 exp(970/RT) cm³ s^?1. An estimate of 91 ± 2 kcal/mol is obtained for the first C? H bond in 1,3,5-trioxane by using a correlation of C? H bond strength with measured activation energies.     

Influence of chemical exchange on the temperature dependence of Eu(fod)3-induced shifts

Temperature dependences of the paramagnetic shifts induced by Eu(fod)₃ in ¹H NMR spectra of ethylene oxide in carbon disulphide solution are obtained in the temperature range from +40 to ? 100°C at 100 MHz and from +30 to ?60°C at 60 MHz. The influence of chemical exchange leads to a decrease of the observed paramagnetic shifts with decreasing temperature. It is shown that a modified Swift and Connick equation can be used to describe the observed dependences. Upper limits of the mean lifetimes of the Eu(fod)₃-ethylene oxide adduct are τ_p < 1·7 × 10^?8 s at 14 °C and τ_p < 1 × 10^?8 s at 20 °C, respectively. The corresponding activation energy is equal to V_a = 13·7 kcal/mol.     

Thermodynamic Studies of Bi-Univalent Electrolytes. VI. Thermodynamics of Cadmium Acetate from E. M. F. and Calorimetric Measurements

E. M. F. of the Cell, Cd-Hg (2-phase)/CdAc₂(m), Hg₂Ac₂(s)/Hg was measured at 20°, 25°, 30° and 40°C. The standard e. m. f. of the cell, Cd/CdAc₃(m), Hg₂Ac₂(c)/Hg was evaluated as E°=1.1500?11.09×10^?4T+1.06×10^?8T² The thermodynamic data of the reaction, Cd(c) + Hg₂Ac₂(c)=2Hg(l)+Cd⁺⁺(aq)+2Ac^?(aq) at 25°C were estimated as ΔF°=?42,139, ΔH°=?48,698 cal mole^?1 and ΔS°=?22.0 cal deg^?1 mole^?1 at 25°C. The thermodynamic data for the formation of Hg₂Ac₂(s) were evaluated as ΔF_f°=?202.3, ΔH_f°=?154.5 Kcal mole^?1 and S°=72.9 cal deg^?1 mole^?1. From measurements of the heats of solution of CdAc₂·2H₂O in aqueous solution, the relative partial molal enthalpies of cadmium acetate in aqueous solution were estimated.