Rate constants for the gas-phase reactions of O3 with a series of Terpenes and OH radical formation from the O3 reactions with Sesquiterpenes at 296 ± 2 K

Rate constants for the gas-phase reactions of O₃ with the sesquiterpenes α-cedrene, α-copaene, β-caryophyllene, α-humulene, and longifolene, and with the monoterpenes limonene, terpinolene, α-phellandrene, and α-terpinene, have been measured using a relative rate technique at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in units of 10^?17 cm³ molecule^?1 s^?1) are: limonene, 20.1 ± 5.1; terpinolene, 188 ± 67; α-phellandrene, 298 ± 105; α-terpinene, 2110 ± 770; α-cedrene, 2.78 ± 0.71; α-copaene, 15.8 ± 5.6; β-caryophyllene, 1160 ± 430; α-humulene, 1170 ± 450; and longifolene, <0.07, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference organics. Hydroxyl radical formation yields were also determined for the O₃ reactions with the sesquiterpenes, of 0.67 for α-cedrene, 0.35 for α-copaene, 0.06 for β-caryophyllene, and 0.22 for α-humulene, all with estimated overall uncertainties of a factor of ca. 1.5. The tropospheric lifetimes of the sesquiterpenes due to reaction with O₃ are calculated. © 1994 John Wiley & Sons, Inc.     

Rate constants for the gas-phase reactions of the OH radical with a series of monoterpenes at 294 ± 1 K

Using a relative rate technique, rate constants for the gas-phase reactions of the OH radical with a series of monoterpenes have been determined in one atmosphere of air at 294 ± 1 K. Relative to a rate constant for the reaction of OH radicals with 2,3-dimethyl-2-butene of 1.12 × 10^?10 cm³ molecule^?1 sec^?1, the rate constants obtained were (in units of 10^?11 cm³ molecule^?1 sec^?1): α-Pinene, 5.45 ± 0.32; β-pinene, 7.95 ± 0.52; Δ³-carene, 8.70 ± 0.43; d-limonene, 16.9 ± 0.5; α-terpinene, 36.0 ± 4.0; γ-terpinene, 17.6 ± 1.8; α-phellandrene, 31.0 ± 7.1; myrcene, 21.3 ± 1.6; and ocimene (acis-, trans-mixture), 25.0 ± 1.9. These are the first quantitative kinetic data reported for many of these monoterpenes. The rate constants obtained are compared with the available literature data and with a priori estimates based on the number and configuration of substituents around the double bond(s). The tropospheric lifetimes of these monoterpenes with OH radicals, NO₃ radicals and O₃ are estimated and compared. Atmospheric lifetimes with respect to reaction with the OH radical are calculated to range from ～0.75 hr for α-terpinene to ～5 hr for α-pinene.     

Time‐Resolved Crystallography of the Reaction Intermediate of Nitrile Hydratase: Revealing a Role for the Cysteinesulfenic Acid Ligand as a Catalytic Nucleophile

The reaction mechanism of nitrile hydratase (NHase) was investigated using time‐resolved crystallography of the mutant NHase, in which βArg56, strictly conserved and hydrogen bonded to the two post‐translationally oxidized cysteine ligands, was replaced by lysine, and pivalonitrile was the substrate. The crystal structures of the reaction intermediates were determined at high resolution (1.2–1.3 Å). In combination with FTIR analyses of NHase following hydration in H₂¹⁸O, we propose that the metal‐coordinated substrate is nucleophilically attacked by the O(SO^?) atom of αCys114‐SO^?, followed by nucleophilic attack of the S(SO^?) atom by a βArg56‐activated water molecule to release the product amide and regenerate αCys114‐SO^?.     

Kinetics and mechanism of reactions between aromatic olefins and hydroxyl radicals

The rates of the reactions of hydroxyl radicals (OH) with styrene, α-methylstyrene, and β-methylstyrene have been measured by irradiating mixtures of these aromatic olefins and NO in an environmental chamber at 298 K. Experimental conditions were used whereby the competition of ozone with OH in oxidizing the hydrocarbons could be considered negligible. The rate constant values, obtained by a relative method using isooctane as reference hydrocarbon, are: styrene (5.3 ± 0.5) × 10^?11 cm³/molec·s, α-methylstyrene (5.3 ± 0.6) × 10^?11 cm³/molec·s, and β-methylstyrene (6.0 ± 0.6) × 10^?11 cm³/molec·s. A simplified kinetic treatment of the experimental data shows that styrene and β-methylstyrene are stoichiometrically converted to benzaldehyde, suggesting that OH attack occurs only on the aliphatic moiety of the aromatic olefins. Benzaldehyde was observed to undergo consecutive oxidation by OH, and its maximum formation yield was about 60%. A reaction mechanism is proposed where the primary rate-determining OH attack leads to the formation of 1-hydroxy-2-phenyl-2-ethenyl radicals, from which benzaldehyde is formed through fast intermediate reactions.     

On the tri-n-octylammonium chlorocomplexes of Sn(IV) in benzene solution

Extracts with tri-n-octylammonium chlorocomplexes of Sn(IV) of various compositions, included the N-deuterated compounds, were prepared and investigated by IR spectroscopy and conductivity measurements. Three Sn(IV) complexes were found: (TOAH⁺)₂SnCl₆^2? (2:1-complex), TOAH⁺SnCl₅^? (1:1-complex) and a complex with the stoichiometric ratio TOA:Sn(IV) > 2. The cation of the latter contains the groups (TOAH…Cl…HTOA)⁺ and TOAH⁺ and that species is supposed to be a 3:1-complex (TOAH…Cl…HTOA)⁺TOAH⁺SnCl₆^2?.     

On the tri-n-octylammonium chlorocomplexes of Sn(II) in benzene solution

Loading experiments in the extraction system TOAH⁺Cl^?/benzene-SnCl₂-HCl and measurements of the IR spectra and the specific conductivities κ of the extracts revealed the occurrence of two Sn(II)complexes: TOAH⁺SnCl₃ (1:1-complex) and (TOAH…Cl…HTOA)⁺SnC1₃^? (2:1-complex). The shift of the νNH frequencies of these complexes with N-deuteration, expressed by the ratio νHN/νND, amounts to 1.33 and 1.28 respectively. This agrees very well with corresponding values of complexes with analogous or similar composition.     

Thermally activated transformations in stable and metastable copper(II) pyrovanadate polymorphs

The structural transformations of α- and β′-Cu₂V₂O₇ phases over the entire temperature range of their existence and α → β′-Cu₂V₂O₇ and β′ → β-Cu₂V₂O₇ polymorphic transitions in α-Cu₂V₂O₇ are described from the crystal-chemical standpoint. Variations in the parameters of the polyhedral blocks of the α-Cu₂V₂O₇ structure implies that the greatest deformations occur with a negative and near-zero bulk thermal expansion in the range from room temperature to 400°C. The compression and rotation of vanadium-oxygen diortho groups is accompanied by unbending of zigzag copper-oxygen chains, with the distances between them unchanged, which is the reason for the anomalous volume expansion of the structure. Thermal distortion of β′-Cu₂V₂O₇ is insignificant. The thermal expansion coefficients (TECs) of unit cell parameters are as follows: α _a = ?1.36 × 10^?5 1/K, α _b = 1.95 × 10^?5 1/K, α _c = 1.37 × 10^?5 1/K, α_β = ?0.18 × 10^?5 1/K, and α _V = 1.93 × 10^?5 1/K. We demonstrate that the low-temperature Cu₂V₂O₇ phase can be formed without admixtures of metastable β-Cu₂V₂O₇ upon slow cooling (at about 1 K/min) of the high-temperature phase.     

Spectrophotometric and potentiometric study of the cobalt(II)-thiocyanate system in aqueous medium

The cobalt(II)—thiocyanate system was spectrophotometrically studied at 2.0 M ionic strength (NaClO₄) and 25°C. The following formation constants were obtained: β₁ = 6.9 M^?, β₂ = 28.9 M^?2, β₃ = 12.1 M^?3 and β₄ = 1.30 M^?4. Three wavelengths were considered, 515, 590 and 615 nm, and the molar absorptivities of each species were calculated. Linear relationships were obtained for $\text{ε}$ vs $\text{n}$ and α_i. There is strong evidence that the tetrahedral [Co(SCN)₄]^2? is virtually the only species absorbing at 590 and 615 nm. An indirect potentiometric method led to comparable equilibrium constants. The cadmium(II)—thiocyanate formation constants used in the indirect method, under the same conditions, were found to be β₁ = 21.51 ± 0.09 M^?1, β₂ = 123 ± 1 M^?2, β₃ = 130 ± 3 M^?3 and β₄ = 173 ± 1.2 M^?4, in good agreement with earlier literature data.     

A Kinetic Method For The Determination Of A Nanogram Amount Of Mercury(ii) By Its Catalytic Effect On The Complex Formation Reaction Of Manganese(11) With α, β, γ δ-Tetraphenylporphinesulfonate

Abstract

Mercury(II) ion accelerates the complex formation reaction of manganese(II) with α, β, γ δ-tetraphenylporohinesulfonate (TPPS). Mercury(II) concentrations as low as 10^?8 mol dm^?3 can be determined from the decrease in absorbance at 413 nm (Λ_max of TPPS) at a fixed time after the initiation of the reaction of rnanganese(II) with TPPS. Sandell's sensitivity calculated from the calibration curve at 30 min after the start of the reaction is 3.8 × 10^?2 ng cm^?2. After the separation of metallic mercury by distillation at room temperature, the method is highly selective and is free from interference of most substances usually encountered.     

β-Ketonitrosamines as Synthetic Equivalents of α-Methinyl Methylamino (R-Chnhch3) and α-Methinyl Alkylamino (R−Chnhr′) Anions

Abstract

β-Ketonitrosamines have been established as anionic synthons of the type (RCO^{+ ?}CHNHR′). The enhanced acidity of protons at the α-carbon, as well as the ease of fragmentation of the title compounds, established them as synthetic equivalents of α-methylenealkylamino anions (^?CH2NHR). We now report the equivalency of β-ketonitrosamines to α-methinyl methylamino (R^?CHNHCH₃) and α-methinyl alkylamino (R ^?CHNHR′) anions.     

Stereoselective cyanation of β-bromo-β-fluorostyrenes using potassium cyanide and promoted by (CH3CN)4Cu+ BF4−

A general method for the synthesis of α-fluorocinnamonitrile based on the stereoselective reaction between β-bromo-β-fluorostyrene and potassium cyanide, promoted by (CH₃CN)₄Cu⁺ BF₄^? in 1-methyl-2-pyrrolidinone (NMP), is described.     

A Selective Fluorimetric Method for the Determination of Some β-Lactamic AntibioticsSupported by Natural Science Foundations of China and Shandong province

Abstract

Based on the reaction between acetylacetone-formaldehyde and β-lactamic antibiotics at pH=4.0, in which product can emit strong fluorescence, a selective simple fluorimetric method is described for the determination of both α-aminocephalosporins (namely cepharadine and cefalexin) and 6-aminopenicillanic acid (6-APA) in pure form and in pharmaceutical form. Other β-lactamic antibiotics free from α-amino group do not interfere with the assay. The linear ranges are 1.0×10^?4-8.0×10^?2 mg/ml, 2.0×10^?4-3.0×10^?2 mg/ml and 3.0×10^?4-2.0×10^?2mg/ml for cepharadine, cefalexin and 6-APA, respectively. Their detection limits (S/N=3) are 3.0×10^?5mg/ml, 4.0×10^?5mg/ml and 6.0×10^?5mg/ml.     

Kinetics of the gas-phase reactions of β-phellandrene with OH and NO3 radicals and O3 at 297 ± 2 K

Rate constants for the gas-phase reactions of the biogenically emitted monoterpene β-phellandrene with OH and NO₃ radicals and O₃ have been measured at 297 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm³ molecule^?1 s^?1 units): for reaction with the OH radical, (1.68 ± 0.41) × 10^?10; for reaction with the NO₃ radical, (7.96 ± 2.82) × 10^?12; and for reaction with O₃, (4.77 ± 1.23) × 10^?17, where the error limits include the estimated uncertainties in the reference reaction rate constants. Using these rate constants, the lifetime of β-phellandrene in the lower troposphere due to reaction with these species is calculated to be in the range of ca. 1–8 h, with the OH radical reaction being expected to dominate over the O₃ reaction as a loss process for β-phellandrene during daylight hours.     

Étude comparative,par spectroscopie infrarouge,des vibrations v(ch) de quelques alcools et thiols ne comportant qu'un seul vibrateur ch

Infrared spectra of some deuterated alcohols and thiols with only one α-CH or β-CH have been obtained in order to compare α and β heteroatom effects on v(CH). The spectra of RR'CHOH alcohols show two bands (Δv? 50 cm^?1) due to the α-CH bond trans to an oxygen lone-pair and the α-CH bond trans to OH.The α sulphur effect is found very weak or non-existent in thiols. The study of CD₂H-CD ₂OH and CD₂HCD₂SH spectra shows the same β-gauche effect of both the heteroatoms while only the sulphur atom seems to have a β-trans effect.     

Heterogeneous versus Homogeneous Copper(II) Catalysis in Enantioselective Conjugate‐Addition Reactions of Boron in Water

We have developed Cu^II‐catalyzed enantioselective conjugate‐addition reactions of boron to α,β‐unsaturated carbonyl compounds and α,β,γ,δ‐unsaturated carbonyl compounds in water. In contrast to the previously reported Cu^I catalysis that required organic solvents, chiral Cu^II catalysis was found to proceed efficiently in water. Three catalyst systems have been exploited: cat. 1: Cu(OH)₂ with chiral ligand L1 ; cat. 2: Cu(OH)₂ and acetic acid with ligand L1 ; and cat. 3: Cu(OAc)₂ with ligand L1 . Whereas cat. 1 is a heterogeneous system, cat. 2 and cat. 3 are homogeneous systems. We tested 27 α,β‐unsaturated carbonyl compounds and an α,β‐unsaturated nitrile compound, including acyclic and cyclic α,β‐unsaturated ketones, acyclic and cyclic β,β‐disubstituted enones, acyclic and cyclic α,β‐unsaturated esters (including their β,β‐disubstituted forms), and acyclic α,β‐unsaturated amides (including their β,β‐disubstituted forms). We found that cat. 2 and cat. 3 showed high yields and enantioselectivities for almost all substrates. Notably, no catalysts that can tolerate all of these substrates with high yields and high enantioselectivities have been reported for the conjugate addition of boron. Heterogeneous cat. 1 also gave high yields and enantioselectivities with some substrates and also gave the highest TOF (43 200 h^?1) for an asymmetric conjugate‐addition reaction of boron. In addition, the catalyst systems were also applicable to the conjugate addition of boron to α,β,γ,δ‐unsaturated carbonyl compounds, although such reactions have previously been very limited in the literature, even in organic solvents. 1,4‐Addition products were obtained in high yields and enantioselectivities in the reactions of acyclic α,β,γ,δ‐unsaturated carbonyl compounds with diboron 2 by using cat. 1, cat. 2, or cat. 3. On the other hand, in the reactions of cyclic α,β,γ,δ‐unsaturated carbonyl compounds with compound 2 , whereas 1,4‐addition products were exclusively obtained by using cat. 2 or cat. 3, 1,6‐addition products were exclusively produced by using cat. 1. Similar unique reactivities and selectivities were also shown in the reactions of cyclic trienones. Finally, the reaction mechanisms of these unique conjugate‐addition reactions in water were investigated and we propose stereochemical models that are supported by X‐ray crystallography and MS (ESI) analysis. Although the role of water has not been completely revealed, water is expected to be effective in the activation of a borylcopper(II) intermediate and a protonation event subsequent to the nucleophilic addition step, thereby leading to overwhelmingly high catalytic turnover.     

Ab initio study of β-lactam antibiotics. I. Potential energy surface for the amidic CN bond breaking in the β-lactam + OH− reaction

The potential energy surface of the β-lactam + OH^? reaction, related to the mode of action of β-lactam antibiotics, was investigated using the ab initio Hartree—Fock method with the STO-3G basis set. Three possible reaction paths for the B_AC2 breaking of the amidic CN bond were obtained and discussed. The minimum-energy reaction path is characterized by the following processes: (1) the formation of a tetrahedral intermediate, ≈ 121 kcal mol^?1 more stable than the reagents; (2) a barrier, ≈ 15 kcal mol^?1 above the intermediate, which is mainly due to the partial breaking of the amidic bond; (3) the complete breaking of the amidic bond concerted with a proton transfer till the formation of the final product, ≈ 34 kcal mol^?1 more stable than the intermediate. The evolution of some molecular orbitals and of the electron population along the reaction path was also discussed.     

Extension de la reaction de Wittig: Condensation “d'ylures enolates” sur les cetones aliphatiques

The enolate ylide Ph₃P⁺C^?C(Ph)O^?Li₊ obtained by the reaction of HMPT-Li with the benzoylmethylenetriphenylphosphorane Ph₃PCHCOPh reacts with aliphatic ketones, in contrast to its precursor. This condensation makes it possible to prepare β,γ-unsaturated ketones, of type RCHC(R′)CH₂COPh, instead of the α,β isomer usually obtained in a Wittig reaction.     

Spectroscopic characterization of the binding and isomerization cycle of Brooker’s merocyanine with α-, β-, and γ-cyclodextrins

Complexes of Brooker’s merocyanine dye with α-, β- and γ-cyclodextrin (CD) have been characterized to determine the relative strength and thermodynamics of binding, as well as the effect of binding on the protolytic-photochemical isomerization cycle of the dye. It was found that the dye binds most tightly to β-CD, with a binding equilibrium constant of 430 M^?1, in agreement with previous results (Hamasaki et al. J. Incl. Phenom. Mol. Rec. Chem. 13, 349–359 (1992)), while α-CD and γ-CD complexes have a binding constant of approximately 110 M^?1 and 70 M^?1, respectively, determined using absorbance and fluorescence spectroscopy. The isomerization cycle for the dye in α- and γ-CD complexes was found to be the same as for the free dye. Complexation with β-CD, however, resulted in depressed trans-to-cis photoisomerization in acidic conditions followed by spontaneous cis-to-trans isomerization (with the addition of base). Thermodynamic results also indicated differences between α-CD (ΔS° = ?48 J K^?1) and β-CD (ΔS° =  +12 J K^?1) complexes. There was no temperature dependence observed for the γ-CD complexes. These results can be justified in terms of the location of the dye molecule within the cyclodextrin cavity for each of the complexes.     

Mass spectrometric study on 2-amino-as-triazino[6,5-c]quinoline and some of its derivatives

Electron impact induced fragmentations of 2-amino-as-triazino[6,5-c]quinoline and its 2-methylamino, 2-dimethylamino and 2-benzylamino analogues have been investigated. The main primary decomposition route of both the singly and the doubly charged molecular ions is the N₂ loss. For the singly charged ions the critical energy of this reaction is 110±10 kJ mol^?1 and the kinetic energy release is 61±4 kJ mol^?1. For the doubly charged ions these values are 90±10 kJ mol^?1 and 5±2 kJ mol^?1, respectively, indicating a significantly different reaction profile. The further fragmentation of [M? N₂]⁺˙ ions consists of radical eliminations from the 2-amino group with cleavages of the α- and β-bonds. Here a significant substituent effect is eliminations found suggesting an intramolecular cyclization reaction with a substituent migration. D and ¹⁵N labelling experiments have shown a minor extent of randomization of the labelled atoms and the occurrence of other hidden skeletal rearrangements during the fragmentation.     

Die Konfiguration der stereoisomeren Tris(glycinato)-Kobalt(III)-Komplexe

It is shown that the stereoisomeric tris(glycinato)cobalt(III) complexes, first prepared by Ley & Winkler, differ in their molecular symmetry. Based on this difference it is possible to assign by ¹³C-NMR. spectroscopy the facial configuration to the red β-complex and the peripheral configuration to the violet α-isomer.