共查询到20条相似文献,搜索用时 15 毫秒
1.
Seung Kyu Min Dr. Mina Park Prof. N. Jiten Singh Prof. Han Myoung Lee Dr. Eun Cheol Lee Prof. Dr. Kwang S. Kim Dr. Anita Lagutschenkov Prof. Dr. Gereon Niedner‐Schatteburg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(34):10373-10379
Protonated and deprotonated adipic acids (PAA: HOOC? (CH2)4? COOH2+ and DAA: HOOC? (CH2)4? COO?) have a charged hydrogen bond under the influence of steric constraint due to the molecular skeleton of a circular ring. Despite the similarity between PAA and DAA, it is surprising that the lowest energy structure of PAA is predicted to have (H2O???H???OH2)+ Zundel‐like symmetric hydrogen bonding, whereas that of DAA has H3O+ Eigen‐like asymmetric hydrogen bonding. The energy profiles show that direct proton transfer between mirror image structures is unfavorable. Instead, the chiral transformation is possible by subsequent backbone twistings through stepwise proton transfer along multistep intermediate structures, which are Zundel‐like ions for PAA and Eigen‐like ions for DAA. This type of chiral transformation by multistep intramolecular proton transfers is unprecedented. Several prominent OH???O short hydrogen‐bond stretching peaks are predicted in the range of 1000–1700 cm?1 in the Car–Parrinello molecular dynamics (CPMD) simulations, which show distinctive signatures different from ordinary hydrogen‐bond peaks. The O? H? O stretching peaks in the range of 1800–2700 cm?1 become insignificant above around 150 K and are almost washed out at about 300 K. 相似文献
2.
Raman spectra have been recorded for monodisperse and polydisperse samples of oligooxyethylene at several temperatures in the range 310–77 K. Four scattering peaks are found with frequency dependent on temperature. One at 92–80 cm?1 is unaffected by changes in chain length and is assigned to a lattice mode. The others are chain-length dependent and are assigned either to the longitudinal acoustical modes (LAM-1 and LAM-3)or, less certainly, to a transverse acoustical mode. 相似文献
3.
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 T2.46 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. 相似文献
4.
Relative rate constants for the reaction of OH radicals with a series of n-alkanes have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10?12 cm3 molecule?1s?1, the rate constants obtained are (X1012 cm3 molecule?1 s?1): propane 1.22 ± 0.05, n-pentane 4.13 ± 0.08, n-heptane 7.30 ± 0.17, n-octane 9.01 ± 0.19, n-nonane 10.7 ± 0.4, and n-decane 11.4 ± 0.6. The data for propane, n-pentane, and n-octane are in good agreement with literature values, while those for n-heptane, n-nonane, and n-decane are reported for the first time. These data show that the rate constant per secondary C—H bond is ∽40% higher for —CH2— groups bonded to two other —CH2— groups than for those bonded to a —CH2— group and a —CH3 group. 相似文献
5.
We study dynamics of the CH3 + OH reaction over the temperature range of 300–2500 K using a quasiclassical method for the potential energy composed of explicit forms of short‐range and long‐range interactions. The explicit potential energy used in the study gives minimum energy paths on potential energy surfaces showing barrier heights, channel energies, and van der Waals well, which are consistent with ab initio calculations. Approximately, 20% of CH3 + OH collisions undergo OH dissociation in a direct‐mode mechanism on a subpicosecond scale (<50 fs) with the rate coefficient as high as ~10?10 cm3 molecule?1 s?1. Less than 10% leads to the formation of excited intermediates CH3OH? with excess vibrational energies in CO and OH bonds. CH3OH? stabilizes to CH3OH, redissociates back to reactants, or forms one of various products after intramolecular energy redistribution via bond dissociation and formation on the time scale of 50–200 fs. The principal product is 1CH2 (k being ~10?11), whereas ks for CH2OH, CH2O, and CH3O are ~10?12. The minor products are HCOH and CH4 (k~10?13). The total rate coefficient for CH3 + OH → CH3OH? → products is ~10?11 and is weakly dependent on temperature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 455–466, 2011 相似文献
6.
The gas phase reaction of the hydroxyl radical with the unsaturated peroxyacyl nitrate CH2 ? C(CH3)C(O)OONO2 (MPAN) has been studied at 298 ± 2 K and atmospheric pressure. The OH-MPAN reaction rate constant relative to that of OH + n-butyl nitrate is 2.08 ± 0.25. This ratio, together with a literature rate constant of 1.74 × 10?12 cm3 molecule?1 s?1 for the OH + n-butyl nitrate reaction at 298 K, yields a rate constant of (3.6 ± 0.4)× 10?12 cm3 molecule?1 s?1 for the OH-MPAN reaction at 298 ± 2 K. Hydroxyacetone and formaldehyde are the major carbonyl products. The yield of hydroxyacetone, 0.59 ± 0.12, is consistent with preferential addition of OH at the unsubstituted carbon atom. Atmospheric persistence and removal processes for MPAN are briefly discussed. © 1993 John Wiley & Sons, Inc. 相似文献
7.
The rate coefficients for the reaction OH + CH3CH2CH2OH → products (k1) and OH + CH3CH(OH)CH3 → products (k2) were measured by the pulsed‐laser photolysis–laser‐induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k1 and k2 are as follows: k1 = (6.2 ± 0.8) × 10?12 exp[?(10 ± 30)/T] cm3 molecule?1 s?1, with k1(298 K) = (5.90 ± 0.56) × 10?12 cm3 molecule?1 s?1, and k2 = (3.2 ± 0.3) × 10?12 exp[(150 ± 20)/T] cm3 molecule?1 s?1, with k2(298) = (5.22 ± 0.46) × 10?12 cm3 molecule?1 s?1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n‐propanol and iso‐propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10?19 and (1.90 ± 0.10) × 10?18 cm2 molecule?1, respectively. The atmospheric implications of the degradation of n‐propanol and iso‐propanol are discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 10–24, 2010 相似文献
8.
IR spectra are plotted from anilides of 1-piperidine carboxylic acids C5H10N(CH2)n CONHC6H4R in CHCl3 and CDCl3 solutions. In the cases of n = 1 and n = 4, weak intramolecular (NH?N) hydrogen bonds are formed. An asymmetrical energy surface occurs and the proton is present at the N of the anilide group. In the cases of n = 2 and n = 3, intramolecular proton transfer hydrogen bonds of the types NBH?NP ? ?NB?H+Np are formed. In contrast to the intramolecular OH? N ? O?1 ? H+N bonds with 1-piperidine carboxylic acids, these bonds to not cause IR continua but two bands: one in the region 3250–3190 and one in the region 2500–2450 cm?1. The fact that, instead of IR continua, bands are observed is explained by the following: (1) these hydrogen bonds are relatively long; (2) they show only a narrow distribution of bond length; (3) the electrical fields at these bonds are small, since they are strongly screened. 相似文献
9.
Pedro D. Vaz Dr. Mariela M. Nolasco Dr. Francisco P. S. C. Gil Dr. Paulo J. A. Ribeiro‐Claro Prof. John Tomkinson Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(30):9010-9017
Spectroscopic evidence for C? H ??? O hydrogen bonding in chloroform ??? acetone [Cl3CH ??? O?C(CH3)2] mixtures was obtained from vibrational inelastic neutron scattering (INS) spectra. Comparison between the INS spectra of pure samples and their binary mixtures reveals the presence of new bands at about 82, 130 and 170 cm?1. Assignment of the 82 cm?1 band to the νO ??? H anti‐translational mode is considered and discussed. In addition, the βC? H mode of CHCl3 at 1242 cm?1 is split in the spectra of the mixtures, and the high‐wavenumber component is assigned to the hydrogen‐bonded complex. The plot of the integrated intensity of this component shows a maximum for x=0.5, in agreement with the 1:1 stoichiometry of the chloroform ??? acetone complex, with a calculated complexation constant of 0.15 dm3 mol?1. Results also show that the complex behaves as an independent entity, that is, despite being weak, such interactions play a key role in supramolecular chemistry. 相似文献
10.
The collisional activation mass spectra prove that non-decomposing ionized methyl acetate [CH3COOCH3]+? and its enolic isomer [CH2?C(OH)OCH3]+? exist as stable species in potential wells. It is shown, however, that prior to CH3O? loss the decomposing [CH2?C(OH)OCH3]+? ion isomerizes via a rate determining symmetry forbidden [1.3] hydrogen rearrangement to ionized methyl acetate. The alternative mode of two consecutive formally symmetry allowed [1.2] hydrogen migrations can be certainly excluded for this isomerization. The activation energy of such hydrogen rearrangements is of the order of 41–83 kcal · mol?1 depending on the electronic nature of the cations (“open” or “closed” shell systems). 相似文献
11.
Two new doubly methoxido-bridged MnIII dinuclear complexes, [MnIII(mphp)(μ-OCH3)(CH3OH)]2·2CH3OH (1) and ([MnIII(ahbz)(μ-OCH3)(CH3OH)]2·2CH3OH (2), have been synthesized by using the tridentate ligands H2mphp (H2mphp = 2-methyl-6-(pyrimidin-2-yl-hydrazonomethyl)-phenol) and H2ahbz (H2ahbz = N-(2-amino-propyl)-2-hydroxy-benzamide). The complexes have been characterized by single-crystal X-ray diffraction analysis and magnetic measurements. Complexes 1 and 2 have a similar dimeric molecular structure. Two [Mn(L)(CH3OH)]+ moieties (L2? = mphp2? or ahbz2?) are bridged by two μ-OCH3? groups in the axial-equatorial asymmetric manner. The coordination geometry of MnIII is an axially elongated octahedron with two oxygens of a methanol ligand and a methoxido ligand situated at the axial positions. Magnetic measurements indicate that 1 and 2 exhibit antiferromagnetic behavior with the fitting parameter of J = ?1.49(3) cm?1, D = ?1.3(1) cm?1, g = 1.98(1) and zJ′ = ?0.18(4) cm?1 for 1, and J = ?1.6(2) cm?1, D = 4.5(3) cm?1, g = 2.06(1) and zJ′ = 1.4(1) cm?1 for 2 on the basis of the spin Hamiltonian ? = ?2J?Mn1?Mn2. 相似文献
12.
合成和表征了一个新的杯[4]芳烃衍生物,11,23-二羟亚胺甲基-25,27-二羟基-26,28-二丙氧基杯[4]芳烃 (B)及其与乙腈生成的组成为B·2CH3CN的化合物。1H NMR显示,在B·2CH3CN中B采取锥型构象,X-射线衍射分析确证在溶液中所发现的构象。在晶格网络中存在着B·2CH3CN以二聚体形式的自插入现象。在B3LYP/6-311G(d)水平上计算了该自插入二聚体中的非共价相互作用能,并对基集叠加误差进行了校正。在二聚体中的B·2CH3CN,一个CH3CN通过与羟亚胺基形成氢键使之稳定,结合能为–5.02 kJ·mol-1,另一个CH3CN则通过与另一个羟亚胺基形成氢键以及与另一B·2CH3CN中B苯环空腔间的C–H···π相互作用使之稳定,结合能分别为–14.23 kJ·mol-1和–3.77 kJ·mol-1。自插入的驱动能为–7.54 kJ·mol-1。 相似文献
13.
Synthesis and Characterization of Secondary Nitrosamines from Secondary Amines Using Sodium Nitrite and p‐Toluenesulfonic Acid
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We synthesized nitrosamines (R2N? NO) with R=iPr ( 1 ), nPr ( 2 ), nBu ( 3 ), and hydroxyethyl ( 4 ) from the amine using sodium nitrite/p‐toluenesulfonic acid in CH2Cl2. The rate of formation of 1 – 4 increases in the direction iPr<nPr<nBu2CH2OH. Compounds 1 – 3 were obtained as colorless solids, whereas 4 is a bright yellow liquid. Compounds 1 – 4 were characterized by elemental analysis, MS, IR, and multinuclear NMR (1H, 13C, and 15N) spectroscopies. Additionally, we measured the UV/Vis spectra of all compounds, which show maxima of absorption at approximately 221 nm and molar extinction coefficients between 3043 and 4859 L mol?1 cm?1. We calculated the optimized structures of 1 – 4 (B3LYP/6‐311+G(d,p)) and computed the NMR spectroscopic chemical shifts and infrared frequencies. Furthermore, we carried out a natural bond orbital (NBO) analysis of the nitrosamine moiety. Lastly, the compounds described in this work are valuable starting materials for the synthesis of 2‐tetrazenes with potential interest to replace highly toxic hydrazines in rocket propulsion. 相似文献
14.
Ethanol, its deuterated derivatives (C2H5OD, C2D5OD) and fluoroethanols (CFH2CH2OH, CF3CH2OH) have been isolated in low temperature matrices and investigated in the far-infrared region. From the concentration dependency of the observed bands and from studies of the pure alcohols in the gaseous, liquid, and solid phase it was found that the hydrogen bond stretching frequencies νσ associated with the hydrogen bonded system OH?O appear in the 100 – 160 cm?1 range. At higher M/A ratios the OD(OD) torsion modes τOH are dominating and were identified in the 200 – 300 cm?1 region. The influence of various matrix materials like argon, krypton, xenon, nitrogen and methane on the low frequency spectra of ethanol have also been studied. It was found, that nitrogen and methane matrices produce significant changes in the far infrared spectra. 相似文献
15.
The kinetics of the reaction of O + CH3OCH3 were investigated using fast-flow apparatus equipped with ESR and mass-spectrometric detection. The concentration of O(3P) atoms to CH3OCH3 was varied over an unusually large range. The rate constant for reaction was found to be k = (5.0 ± 1.0) × 1012 exp [(?2850 ± 200/RT)] cm3 mole?1 sec?1. The reaction O + CH3OH was studied using ESR detection. Based on an assumed stoichiometry of two oxygen atoms consumed per molecule of CH3OH which reacts, we obtain a value of k = (1.70 ± 0.66) × 1012 exp [(?2,280 ± 200/RT)] cm3 mole?1 sec?1 for the reaction The results obtained in this study are compared with the results from other workers on these reactions. The observation of essentially equal activation energies in these two reactions is indicative of approximately equal C? H bond strengths in CH3OCH3 and CH3OH. This is in agreement with recent measurements of these bond energies. 相似文献
16.
The crystal structures, magnetic properties, and catalase-like activities of assymmetric dinuclear manganese(III, III) complexes, [Mn2III, III(spa)2(μ-Me3CCO2)(Me3CCO2)(CH3OH)] ( 1 ) and [Mn2III, III(vpa)2(μ-Me3CCO2)(Me3CCO2)(CH3OH)] ( 2 ), (H2spa = 3-salicyclideneamino-1-propanol, H2vpa = O-vanillin), were reported. The crystal structures of complexes 1 and 2 consist of the same discrete asymmetric coordination environment of dinuclear clusters, where the two manganese atoms are bridged by two alkoxo oxygens of the spa or vpa ligands and one bidentate carboxylate ion, whereas an additional oxygen atom of monodentate carboxylate coordinated to the first metal ion, and the second metal ion was coordinated by one oxygen atom of the solvent CH3OH. Magnetic investigations (2–300 K) reveal an intramolecular antiferromagnetic spin exchange interaction with axial-field splittings: J = ?12.3 cm?1 (D = ?0.10 cm?1) and J = ?13.3 cm?1 (D = ?0.15 cm?1) for complexes 1 and 2 , respectively. The complexes should show catalase-like activity for H2O2 disproportionation in CH3OH solvent at 25° with rate constants of k = 6.35 dm3moI?1s?1 and 6.20 dm3mol?1s?1 for complexes 1 and 2 , respectively. 相似文献
17.
《Journal of Coordination Chemistry》2012,65(24):4259-4270
One nonlinear and one linear trinuclear copper(II) complex [Cu3(dien)2(pdc)2CH3OH]2?·?6CH3OH (1) and [Cu3(pdc)2(CH3OH)6(H2O)4] (2) were prepared and characterized structurally, where dien is diethylenetriamine and pdc3? the trianion of 3,5-pyrazoledicarboxylic acid. Both complexes consist of 3,5-pyrazoledicarboxylato-bridged trinuclear copper(II) centers. In 1, copper(II) ions are five-coordinate in distorted square pyramids with bond angles 164.78° for Cu(1)–Cu(2)–Cu(3) and 164.51° for Cu(4)–Cu(5)–Cu(6). In 2, the three copper(II) ions are six-coordinate with elongated octahedral geometry. The trinuclear units of 1 and 2 interact through hydrogen bonds to form 3-D and 2-D supramolecular networks, respectively. Variable temperature magnetic susceptibility measurements show that 1 and 2 are antiferromagnetically coupled with J values of ?11.2 and ?13.3?cm?1. 相似文献
18.
Pranav R. Shirhatti Prof. Dilip K. Maity Surjendu Bhattacharyya Prof. Sanjay Wategaonkar 《Chemphyschem》2014,15(1):109-117
The C?H???Y (Y=hydrogen‐bond acceptor) interactions are somewhat unconventional in the context of hydrogen‐bonding interactions. Typical C?H stretching frequency shifts in the hydrogen‐bond donor C?H group are not only small, that is, of the order of a few tens of cm?1, but also bidirectional, that is, they can be red or blue shifted depending on the hydrogen‐bond acceptor. In this work we examine the C?H???N interaction in complexes of 7‐azaindole with CHCl3 and CHF3 that are prepared in the gas phase through supersonic jet expansion using the fluorescence depletion by infra‐red (FDIR) method. Although the hydrogen‐bond acceptor, 7‐azaindole, has multiple sites of interaction, it is found that the C?H???N hydrogen‐bonding interaction prevails over the others. The electronic excitation spectra suggest that both complexes are more stabilized in the S1 state than in the S0 state. The C?H stretching frequency is found to be red shifted by 82 cm?1 in the CHCl3 complex, which is the largest redshift reported so far in gas‐phase investigations of 1:1 haloform complexes with various substrates. In the CHF3 complex the observed C?H frequency is blue shifted by 4 cm?1. This is at variance with the frequency shifts that are predicted using several computational methods; these predict at best a redshift of 8.5 cm?1. This discrepancy is analogous to that reported for the pyridine‐CHF3 complex [W. A. Herrebout, S. M. Melikova, S. N. Delanoye, K. S. Rutkowski, D. N. Shchepkin, B. J. van der Veken, J. Phys. Chem. A 2005 , 109, 3038], in which the blueshift is termed a pseudo blueshift and is shown to be due to the shifting of levels caused by Fermi resonance between the overtones of the C?H bending and stretching modes. The dissociation energies, (D0), of the CHCl3 and CHF3 complexes are computed (MP2/aug‐cc‐pVDZ level) as 6.46 and 5.06 kcal mol?1, respectively. 相似文献
19.
Geoffrey S. Tyndall Thomas A. Staffelbach John J. Orlando Jack G. Calvert 《国际化学动力学杂志》1995,27(10):1009-1020
Rate coefficients have been measured for the reaction of OH radicals with methylglyoxal from 260 to 333 K using the discharge flow technique and laser-induced fluorescence detection of OH. The rate coefficient was found to be (1.32±0.30) × 10?11 cm3 molecule?1 s?1 at room temperature, with a distinct negative temperature dependence (E/R of ?830 ± 300 K). These are the first measurements of the temperature dependence of this reaction. The reaction of OH with acetaldehyde was also investigated, and a rate coefficient of (1.45 ± 0.25) × 10?11 cm3 molecule?1 s?1 was found at room temperature, in accord with recent studies. Experiments in which O2 was added to the flow showed regeneration of OH following the reaction of CH3CO radicals with O2. However, chamber experiments at atmospheric pressure using FTIR detection showed no evidence for OH production. FTIR experiments have also been used to investigate the chemistry of the CH3COCO radical formed by hydrogen abstraction from methylglyoxal. © 1995 John Wiley & Sons, Inc. 相似文献
20.
The kinetics of the gas-phase reactions of allyl chloride and benzyl chloride with the OH radical and O3 were investigated at 298 ± 2 K and atmospheric pressure. Direct measurements of the rate constants for reactions with ozone yielded values of ??(O3 + allyl chloride) = (1.60 ± 0.18) × 10?18 cm3 molecule?1 s?1 and ??(O3 + benzyl chloride) < 6 × 10?20 cm3 molecule?1 s?1. With the use of a relative rate technique and ethane as a scavenger of chlorine atoms produced in the OH radical reactions, rate constants of ??(OH + allyl chloride) = (1.69 ± 0.07) × 10?11 cm3 molecule?1 s?1 and ??(OH + benzyl chloride) = (2.80 ± 0.19) × 10?12 cm3 molecule?1 s?1 were measured. A study of the OH radical reaction with allyl chloride by long pathlength FT-IR absorption spectroscopy indicated that the co-products ClCH2CHO and HCHO account for ca. 44% of the reaction, and along with the other products HOCH2CHO, (ClCH2)2CO, and CH2 ? CHCHO account for 84 ± 16% of the allyl chloride reacting. The data indicate that in one atmosphere of air in the presence of NO the chloroalkoxy radical formed following OH radical addition to the terminal carbon atom of the double bond decomposes to yield HOCH2CHO and the CH2Cl radical, which becomes a significant source of the Cl atoms involved in secondary reactions. A product study of the OH radical reaction with benzyl chloride identified only benzaldehyde and peroxybenzoyl nitrate in low yields (ca. 8% and ?4%, respectively), with the remainder of the products being unidentified. 相似文献