Chlorination of ammonia and aliphatic amines by Cl2: DFT study of medium and substituent effects

The mechanism of chlorination of ammonia and aliphatic amines by Cl₂ was studied by quantum‐chemical calculations using a series of DFT functionals. Three different reaction pathways were considered for the reaction between Cl₂ and NH₃ in the gas phase. Several intermediates and transition state structures, not described earlier, were located on the corresponding potential energy surface. It is calculated that the reaction field effects (SCIPCM) on the chlorination is much less pronounced than the effect of a specific solvent interaction which was modeled by an explicit water molecule. It is also found that the calculated energy barrier and the reaction free energy of the chlorination of different amines are dependent on the alkyl‐substituent effects. With increase in the basicity of amine, the chlorination reaction becomes more feasible. Calculated geometries of intermediates and overall reaction energetics are significantly influenced by the method for a treatment of electron correlation (DFT vs. MP2), and by the fraction of HF exchange (χ) in DFT functionals. With increase in the χ in the corresponding functional, the DFT results approach those obtained at the MP2 level, and are closer to experimental values, as well. Copyright © 2008 John Wiley & Sons, Ltd.     

A new level at 192.5 keV in Ge

In the experiments on ⁷⁴Ge(d, pγ)⁷⁵Ge, a 52.5±0.1 keV γ-ray was found in ⁷⁵Ge with a half-life of 216±5 ns. From the analysis of the γ-ray spectra the conversion coefficient of the 52.5 keV γ-ray was determined. Then, a new level of is confirmed to exist at 192.5 keV. The reduced transition probabilities of the 52.5 keV transition are deduced to be (6.9^+5.6 _−2.1) × 10⁻⁵ for B(M1) and 31⁺³ ₋₂ for B(E2) in Weisskopf units.     

An unexpected C–C cleavage reaction: new and mild access to <Emphasis Type="Italic">o</Emphasis>-OH and <Emphasis Type="Italic">o</Emphasis>-NH-Tos benzoic acids or benzoamides

Catalyzed by DBU or DBN, 2-acetoxy benzofuranones and 2-acetoxy-N-Tos indolin-3-ones, were readily prepared from o-acyl phenols and o-acyl anilines, respectively, reacted with H₂O or a range of amines to afford o-OH and o-NH-Tos benzoic acids or benzoamides in moderate to excellent yields.     

Theoretical study on the mechanism for NH3BH3 reduction of ketones and imines

In spite of a potential hydrogen storage material, ammonia borane (AB) was recently found to be a good hydrogenation reagent. It can reduce certain ketones to alcohols or borate esters, and imines to amines. The mechanisms of these reactions are not fully understood yet, and have been systematically studied using high-level CCSD(T) calculations in this work. We have validated theoretically that the forming of alcohols and amines undergoes concerted double-hydrogen transfer (DHT) mechanism. Furthermore, we predicted that the DHT process is facile for more general ketones and imines. For the borate ester formation, we found a pretty high barrier for the experimentally derived stepwise mechanism. Alternatively, we propose that the reaction starts with the DHT process to form alcohol and NH₂BH₂, followed by alcoholysis of NH₂BH₂ to form the first B–O bond. This mechanism is in good agreement with the current experimental facts, and also explains why ketone reduction affords different products at different conditions. For these reaction systems, the performances of M06-2x and MP2 (underestimate the barrier by 5–7 kcal/mol, but with right trends) are better than B3LYP and BLYP methods (underestimate the barrier by 0–5 kcal/mol).     

Kinetics and mechanism of the reactions of aryl chlorodithioformates with pyridines and secondary alicyclic amines

The reactions of pyridines and secondary alicyclic (SA) amines with phenyl and 4‐nitrophenyl chlorodithioformates (PClDTF and NPClDTF, respectively) are subjected to a kinetic study in aqueous ethanol (44 wt% ethanol) solution, at 25.0 °C, and an ionic strength of 0.2 M (KCl). The reactions are studied spectrophotometrically. Under amine excess, pseudo‐first‐order rate coefficients (k_obs) are found. Plots of k_obs versus [amine] are linear and pH independent, with slope k_N. The Brønsted‐type plots (log k_N vs. pK_a of aminium ions) are linear for the reactions of PClDTF with SA amines (slope β of 0.3) and pyridines (β = 0.26) and those of NPClDTF with pyridines (β = 0.30). For the reaction of NPClDTF with SA amines the Brønsted‐type plot is biphasic, with slopes β₁ = 0.2 (at high pKa) and β₂ = 1.1 (at low pKa). The pK_a value at the center of curvature (pK) is 7.7. The magnitude of the slopes indicates that the mechanisms of these reactions are stepwise, with the formation of a zwitterionic tetrahedral intermediate as the rate‐determining step, except for the reaction of NPClDTF with SA amines where there is a change in the rate‐determining step, from formation to breakdown of the tetrahedral intermediate, as the amine basicity decreases. Copyright © 2009 John Wiley & Sons, Ltd.     

Isoscalar quadrupole strength in Ca from the (p,p′α0) reaction at Ep = 100 MeV

The ⁴⁰Ca(p,p′ α) reaction has been studied at an incident proton energy E_p = 99.5 MeV for proton laboratory scattering angles Θ_p^lab = 17°, 23° and 27°. Emission of α particles coincident with the scattered proton has been measured for an angular range Θ_α 0° − 180° relative to the recoil axis. A multipole decomposition for the α₀-decay channel to the ³⁶Ar ground state has been performed from the angular-correlation functions. The energy distribution of the dominating E2 strength deduced in the excitation energy range E_x = 11–21 MeV agrees reasonably well with the results from electron and α-induced α₀-decay investigations. The exhaustion of the E2 energy-weighted sum rule in this channel up to an energy of 17 MeV is 16.1(4.0)%, in accord with the study of the (α, α′ α₀) reaction. However, this value is twice what is found in the (e,e′ α₀) experiment in the same energy region. Thus, the puzzling discrepancy in the E2 strengths derived from electromagnetic and hadronic probes remains unsolved.     

Graph-theoretical parameters for π-MO calculation of a series of aromatic amines in the light of DFT theory: comparison with experimental CT transition energies

Expressions for the energies of the highest occupied π-molecular orbitals of a series of aromatic amines have been derived in terms of the vertex weight h _N (for amine nitrogen) and edge weight k _C–N (for the C–N bond) by representing the amine molecule in terms of vertex- and edge-weighted graphs. Graph-theoretical methods have been used to evaluate the quantities involved in such expressions. The HOMO energies of the amines calculated by density functional theory using the 6-31++G** basis set have been correlated with these expressions to estimate the perturbational parameter h _N and the Coulomb integral α. The acceptability of the estimated values of α and h _N has been tested by their ability to explain the experimentally observed trends in the CT transition energies of a series of charge-transfer complexes of amines with tetracyanoethylene. An important structural feature, namely rotation of the –NH₂ group about the C–N bond due to steric repulsion with the nearest H-atom in the case of 1-amino compounds, has been observed by such a correlation. The result agrees well with the DFT-optimized geometries of the structures.     

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.     

The HO4H → O3 + H2O reaction catalysed by acidic,neutral and basic catalysts in the troposphere

A detailed effects of catalyst X (X?=?H₂O, (H₂O)₂, NH₃, NH₃···H₂O, H₂O···NH₃, HCOOH and H₂SO₄) on the HO₄H → O₃?+?H₂O reaction have been investigated by using quantum chemical calculations and canonical vibrational transition state theory with small curvature tunnelling. The calculated results show that (H₂O)₂-catalysed reactions much faster than H₂O-catalysed one because of the former bimolecular rate constant larger by 2.6–25.9 times than that of the latter one. In addition, the basic H₂O···NH₃ catalyst was found to be a better than the neutral catalyst of (H₂O)₂. However it is marginally less efficient than the acidic catalysts of HCOOH, and H₂SO₄. The effective rate constant (k'_t) in the presence of catalyst X have been assessed. It was found from k'_t that H₂O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320?K at 0?km altitude. However, compared with the rate constant of HO₄H → H₂O?+?O₃ reaction, the k _eff values for H₂O catalysed reaction are smaller by 1–2 orders of magnitude, indicating that the catalytic effect of H₂O makes a negligible contribution to the gas phase reaction of HO₄H → O₃?+?H₂O.

Highlights

• A detailed effects of catalyst of H₂O, (H₂O)₂, NH₃, NH₃···H₂O, H₂O···NH₃, HCOOH and H₂SO₄ on the HO₄H → O₃?+?H₂O reaction has been performed.

• From energetic viewpoint, H₂SO₄ exerts the strongest catalytic role in HO₄H → O₃?+?H₂O reaction as compared with the other catalysts.

• At 0 km altitude H₂O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320 K.

• HO₄H → H₂O?+?O₃ reaction with H₂O cannot be compete with the reaction without catalyst, due to the fact that the effective rate constants in the presence of H₂O are smaller.

     

Vibronic coupling and intersystem crossing in aromatic amines

The fluorescence and phosphorescence spectra of the aromatic amines acridan, iminobibenzyl, and carbazole have been measured in Shpolskii matrices at 10 K. Under these conditions the emission exhibits a detailed vibrational structure which has been analyzed. The change of the polarization degree observed within the fluorescence spectra at 77 K, particularly pronounced in acridan and iminobibenzyl, is attributed to vibronic interaction between the closely lying S₁(¹A₁) and S₂(¹B₁) excited states. This process activates a b₁ vibration with a frequency of 1200 cm⁻¹ in the ground state. The appearance of a long-axis (b₁) polarized vibration (700 cm⁻¹) following the out-of-plane polarized 0-0 band of the phosphorescence of these amines at 77 K is suggested to arise from vibronic interactions in the triplet manifold. This second-order spin-orbit coupling (soc) process is superimposed upon the dominant first-order electronic soc mechanism, which couples the lowest π, π^* triplet with high-energy (σ, π)^* singlet states.     

Synthesis,structural aspects and nonlinear optical properties of novel phthalimide derivatives: theoretical and experimental approach

Novel phthalimides ( 1 , 2 , 3 ) possessing variability of cyclic amines have been synthesized and characterized by analytical and spectroscopic techniques. Phthalimide 1 and 2 crystallized in a triclinic system with space group Pī; however, an orthorhombic system with a chiral space group of P2₁2₁2₁ was observed for 3 possessing piperidine cyclic amine. The hydrogen atoms attached to the central chiral carbon were oriented anti to each other resulting in minimum steric repulsion. The occurrence of C–H···O hydrogen bonds in 1 , 2 , 3 enabled the building of several supramolecular structures. Hyperpolarizability 197.6096 Debye Ų calculated for 1 was found to be higher than the hyperpolarizabilities, 138.0836 and 165.2521 Debye Ų measured for 2 and 3 , respectively. Subsequently, phthalimides ( 1 , 2 , 3 ) were assessed for second harmonic generation (SHG) response, and a negligible response was recorded for 1 and 2 ; however, 3 showed a significant response of 14.2 mV. In addition to acentric structure, helical structural motifs identified in 3 could be responsible for its enhanced SHG response. Copyright © 2014 John Wiley & Sons, Ltd.     

Stereodynamics of the O(3P) with H2 (D2) (v=0, j=0) reaction

Quasi-classical trajectory theory is used to study the reaction of O(³P) with H₂ (D₂) based on the ground ³A' potential energy surface (PES). The reaction cross section of the reaction O+H₂ → OH+H is in excellent agreement with the previous result. Vector correlations, product rotational alignment parameters 〈P₂ (j'·k)〉 and several polarized-dependent differential cross sections are further calculated for the reaction. The product polarization distribution exhibits different characteristics that can be ascribed to different motion paths on the PES, arising from various collision energies or mass factors.     

Photoinduced transformations in (As1–xBix)2S3 glass observed by Raman spectroscopy

Raman spectra of (As_1–xBi_x)₂S₃ glass samples with x ≤ 0.2 measured at the excitation with above-bandgap (532 nm) laser light at a relatively low power density (P_exc = 4 kW/cm²) clearly confirm the amorphous character, thereby markedly extending the known compositional interval of existence of the (As_1–xBi_x)₂S₃ glass previously known (x ≤ 0.06). Spectra measured at an increased P_exc (40 kW/cm²) reveal a photostructural transformation in the illuminated area of the glass leading to an additional contribution of Bi–S bonds as well as to an increasing number of cage-type As₄S₄ units with homopolar As–As bonds. A number of new features in a broad range up to about 1,000 cm⁻¹, which emerge in the Raman spectra of the (As_1–xBi_x)₂S₃ glasses with high (x ≥ 0.14) Bi content and increase in intensity with the exposure time, are related to a photochemical transformation, namely, oxidation of arsenic and sulphur on the (As_1–xBi_x)₂S₃ glass surface with formation of units containing arsenate AsO₄³⁻ and sulphate SO₄²⁻ ions. These processes are irreversible and occur only in the presence of a sufficient amount of bismuth.     

A mild and efficient method for the synthesis of a new class of furo[3,2-c]chromenes in aqueous media

An efficient synthesis of 2-hydroxy-3-[2-oxo-2-phenylethylidene]-2-phenyl-2, 3-dihydro-4 H-furo[3, 2-c]chromene-4(2H)-one is described. This involves the reaction between dibenzoylacetylene and 4-hydroxycoumarine in the presence of NaH (10 mol %) in nearly quantitative yield. Treatment of this heterocyclic system with trimethyl chlorosilane in CHCl₃ leads quantitatively to 4-oxo-3-[2-oxo-2-phenylethylidene]-2-phenyl-3H, 4H-furo[3,2-c]chromene-1-ium chloride. Direct addition of nucleophiles, such as alcohols, amines or trialkyl phosphites to this salt in water as the solvent produces functionalized 2-phenyl-4H-furo[3,2-c] chromen derivatives in excellent yields.     

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).     

New approach to surface ionization and drift-tube spectroscopy of organic molecules

A new physical model of ionization of organic molecules from the class of amines on the oxidized surface of transition metals is suggested. According to this model, the process involves the capture of protons or hydroxyl groups forming on the oxide surface upon water molecule adsorption. The adequacy of the model is demonstrated experimentally with test amines, such as Novocaine (procaine), bencaine, Dimedrol (diphenylhydramine), etc. A theory of drift motion of ion beams that includes the space charge effect is proposed. It is shown that the quantity P _i=μj/ε₀ v _g ² (where μ is the ion mobility, j is the ion current density, ɛ₀ is the permittivity, and v _g is the longitudinal velocity of an ionized gas) plays the role of perveance for intense drift ion beams. A new type of drift-tube spectrometer that uses an ion source due to surface ionization is developed.     

Phase stability,thermal, electrical and structural properties of (Bi2O3)1−x−y(Sm2O3)x(CeO2)y electrolytes for solid oxide fuel cells

In this study, (Bi₂O₃)_1?x?y(Sm₂O₃)_x(CeO₂)_y ternary system was synthesized by using solid-state reaction method. Structural, morphological, thermal and electrical properties of the samples were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy, thermo gravimetry/differential thermal analyzer and four-probe method. The XRD measurement results indicated that the samples (x = 10–15, y = 5–10–15–20) had cubic δ-phase crystallographic structure. The phase stability of the samples was checked by the differential thermal analyzer measurements, which indicates most of the samples have stable δ-Bi₂O₃ phase. The electrical conductivity measurement results showed that the electrical conductivity increased with mol% CeO₂ molar ratio at a fixed molar ratio of Sm₂O₃. The highest electrical conductivity obtained for the (Bi₂O₃)_0.65(Sm₂O₃)_0.15(CeO₂)_0.20 system was 1.55 × 10^?2 (Ω.cm)^?1 at 600 °C. The activation energies were also calculated at low temperature range (350–650 °C) which vary from 1.1325 to 1.4460 eV and at high temperature (above 650 °C) which vary from 0.4813 to 1.1071 eV.     

Selectivity of nitro versus fluoro substitution in arenes in their reactions with charged O‐ and S‐nucleophiles

The relative mobility of nitro and fluoro substituents in 1,3‐dinitro‐ and 1‐fluoro‐3‐nitrobenzenes, 3,5‐dinitro‐ and 3‐fluoro‐5‐nitrobenzotrifluorides under the action of the nucleophiles (2ArYH)·K₂CO₃ and ArY^?K⁺ in solution and the nucleophiles ArYH·K₂CO₃ (Y = O, S) under heterogeneous conditions was studied by a competitive method in DMF at 40–140 °C. The unique dependences of ΔΔH^≠ on ΔΔS^≠ and ΔΔH^≠ on ΔΔG^≠ were determined for all the substrates and nucleophiles. The dependence of the mechanistic pathway on the nucleophile is discussed. Two results are relevant to the reactions studied: (i) substituent effects in the nucleophiles (2ArYH)·K₂CO₃ and ArYH·K₂CO₃ on the activation entropies suggest that the entropy favours the displacement of nitro group; (ii) the negative signs of ΔΔH^≠ and ΔΔS^≠ for the reactions of the nucleophiles ArY^?K⁺ indicate that the enthalpy determines the displacement of nitro group. It is concluded that the selectivity of the reactions with aryloxide and arylthioxide ions cannot be explained by the hard–soft acid–base principle only. Copyright © 2007 John Wiley & Sons, Ltd.     

A simple approach to the synthesis of highly functionalized 3-alkylidene-2,3-dihydro-1<Emphasis Type="Italic">H</Emphasis>-pyrrole-2-ol derivatives and related pyrroles

The reaction of various primary amines with acetylenic esters at ambient temperature in THF/H₂O (50:50) produced related enaminones. Subsequently reaction of these in situ prepared enaminones with dibenzoylacetylene leads to 3-alkylidene-2,3-dihydro-1H-pyrrol-2-ol derivatives in good yields. The reaction of these products with various alcohols in the presence of a catalytic amount of HCl produced highly functionalized pyrroles in nearly quantitative yields.     

Can (H2O) n (n = 1–2) as effective catalysts in the CH2OO + H2S reaction under tropospheric conditions?

The addition reaction of CH₂OO?+?H₂S → HSCH₂OOH without and with catalyst X (X?=?H₂O and (H₂O)₂) has been investigated by CCSD(T)-F12a/VTZ-F12//B3LYP/aug-cc-pVTZ method and canonical variational transition state theory with small curvature tunneling correction. When H₂O was introduced in the CH₂OO?+?H₂S reaction, it not only acts as a catalyst for producing HSCH₂OOH, but also plays as a reactant to forming HOCH₂OOH. The formation channel of HSCH₂OOH is more important than the formation channel of HOCH₂OOH with its calculated rate constant larger by 11.0–43.2 times within the temperature 280–320?K. Then, (H₂O)₂ catalysed CH₂OO?+?H₂S → HSCH₂OOH reaction has been taken into account with its rate lower 1.9–4.2 times than the reaction of CH₂OO?+?H₂S → HSCH₂OOH with water. Also, CH₂OO?+?H₂S with H₂O cannot compete with the CH₂OO?+?H₂S reaction without water. This is different from CH₂OO?+?(H₂O)₂ reaction, which is about 4 orders of magnitude larger than the rate constant for CH₂OO?+?H₂O reaction. Such discrepancy is possible because C(CH₂OO)···O(H₂O) interaction has been enhanced more obviously by H₂O as compared to that of C(CH₂OO)···O(H₂S) interaction.