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101.
The reactivity of 2,2-dimethyl-5-methoxyindan-1-ol (1) and 2,2-dimethyl-6-methoxytetral-1-ol (2) radical cations has been studied both in acidic and basic solution. At pH≤4 both 1+ and 2+ undergo CαH deprotonation as the exclusive reaction with k=4.6×104 and 3.2×104 s−1, respectively. In basic solution 1+ and 2+ behave as oxygen acids undergoing −OH-induced αOH deprotonation in a diffusion controlled process (k−OH≈1010 M−1 s−1). An intermediate alkoxyl radical is formed which undergoes a 1,2-hydrogen atom shift in competition with CC β-scission (with 1+) or as the exclusive pathway (with 2+). A behavior which is interpreted in terms of the greater ease of ring-opening of a five membered ring as compared to a six-membered one. 相似文献
102.
Ottaviani P Giuliano M Velino B Caminati W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(2):538-543
The 1:1 molecular complex between oxetane and water has been investigated by using free-jet millimeter-wave spectroscopy. The rotational spectra of five isotopomers (with H(2)O, D(2)O, DOH, HOD and H(2) (18)O) have been assigned. Partial r(0) and r(s) structures of the complex have been derived. The water moiety lies in the plane of symmetry of oxetane, with the "free" hydrogen E with respect to the ring. The oxetane ring appears to be slightly nonplanar, with the C(beta) carbon tilted on the opposite side of the water unity. The three atoms involved in the hydrogen bond adopt a linear arrangement with an O(ring).H distance of about 1.86 A, and the angle between the COC bisector and the O(ring).H bond being congruent with 106 degrees. Additionally, quantum-chemical calculations for the complex were performed and were found to be in agreement with the experimental results. 相似文献
103.
M. Francesca Ottaviani Annalisa Geniali Michela Cangiotti Filippo Mangani 《Research on Chemical Intermediates》2002,28(2-3):117-130
Mastic resin used as a covering film for painting protection was analyzed by electron paramagnetic resonance (EPR) spectroscopy, both as received and upon aging in sun-light. The effect of prolonged exposure to sun-light was mimicked by UV and, more so, by xenon lamp irradiation. Solid mastic presented EPR signals due to radicals trapped by PBN in solution. Data in the literature indicated the formation of acyl radicals (RCO·). These radicals preferentially dissolved in medium polarity solvents. The radical concentration in the solid mastic increased over time more than 50 times upon UV irradiation for 96 h and, even more, by xenon irradiation for 800 h. Also the PBN-trapped radicals in solution increased in concentration by irradiation. Small nitroxide radicals (TEMPO) interacted with a polar fraction of mastic dissolved in methanol, but mainly interacted with low polar mastic molecules in hydrophobic solvents. It was suggested, on the basis of both the PBN-spin trapping data and the TEMPO mobility variation in the solvents at different polarities, that terpenoid molecules partially polymerize by a radical mechanism to form low molecular weight products. A polyaromatic-radical (pyrene-TEMPO) and a biomolecule-radical (doxylcholestane) both interact weakly with mastic molecules in cyclohexane solutions. A positively charged surfactant radical (dimethylammonium-TEMPO bromide) was easily adsorbed onto the solid mastic surface suggesting that detergents are responsible for mastic degradation. In conclusion, this study provided information on the degradation mechanism of mastic resin and on its interacting ability towards external molecules and pollutants. 相似文献
104.
The hydrogen-bonded complex cyclobutanone-water has been studied by Fourier-transform molecular-beam microwave spectroscopy in the frequency range of 6-18.5 GHz. The rotational spectra of ten isotopomers have been assigned and measured. Five of them have been obtained from different isotopic species (or configurations) of water (H2O, D2O, DOH, HOD, and H2 18O). The remaining five correspond to the four singly substituted 13C and to the 18O species of cyclobutanone, observed in natural abundance. For all species the inertial defect is in the range from -10.44 to -10.50 uA2, showing that the cyclobutanone frame is effectively planar and that the water molecule is coplanar to this frame. The hydrogen bond, almost linear, is formed between a water proton and one of the lone pairs of the cyclobutanone oxygen. 相似文献
105.
The present work deals with the evaluation of measurement uncertainty in the determination of carbon dioxide (CO2) concentration in atmosphere, given the high relevance of this greenhouse gas that influences earth climate. In order to carry out CO2 measurements, non dispersive infrared (NDIR) analysers are usually employed as they are stable and scarcely affected by interferences from other air components or pollutants. Typical uncertainty sources are the resolution of the analyser, its time drift and the contributions due to instrument calibration, which is required in order to produce traceable measurement results. The calibration uncertainty takes into account the uncertainty of the composition of the calibration gas mixtures, the instrument repeatability and the possible or residual lack of fit of the adopted mathematical model. 相似文献
106.
This paper presents Constraint Programming as a natural formalism for modelling problems, and as a flexible platform for solving
them. CP has a range of techniques for handling constraints including several forms of propagation and tailored algorithms
for global constraints. It also allows linear programming to be combined with propagation and novel and varied search techniques
which can be easily expressed in CP. The paper describes how CP can be used to exploit linear programming within different
kinds of hybrid algorithm. In particular it can enhance techniques such as Lagrangian relaxation, Benders decomposition and
column generation. 相似文献
107.
This paper presents constraint programming (CP) as a natural formalism for modelling problems, and as a flexible platform for solving them. CP has a range of techniques for handling constraints including several forms of propagation and tailored algorithms for global constraints. It also allows linear programming to be combined with propagation and novel and varied search techniques which can be easily expressed in CP. The paper describes how CP can be used to exploit linear programming within different kinds of hybrid algorithm. In particular it can enhance techniques such as Lagrangian relaxation, Benders decomposition and column generation. 相似文献
108.
Michela Begala Pierluigi Caboni Maria João Matos Giovanna Lucia Delogu 《Tetrahedron letters》2018,59(18):1711-1714
The reaction of 2-hydroxybenzyltriphenylphosphonium bromide with substituted benzoyl chlorides under Wittig conditions, led to 2-phenylbenzofuran derivatives 4a–p and the unexpected formation of 3-benzoyl-2-phenylbenzofuran derivatives 5a–p. Benzoyl chlorides possessing electron-withdrawing groups afforded 3-benzoyl-2-phenylbenzofuran derivatives in higher yields than those with electron-donating groups. This reaction represents a simple and regioselective, one-pot route towards the preparation of deactivated 3-benzoyl-2-phenylbenzofuran compounds which are difficult to obtain by the direct acylation of 2-phenylbenzofurans. 相似文献
109.
110.
We consider the one-dimensional nonlinear Schrödinger equation with Dirichlet boundary conditions in the fully resonant case (absence of the mass term). We investigate conservation of small amplitude periodic solutions for a large measure set of frequencies. In particular we show that there are infinitely many periodic solutions which continue the linear ones involving an arbitrary number of resonant modes, provided the corresponding frequencies are large enough, say greater than a certain threshold value depending on the number of resonant modes. If the frequencies of the latter are close enough to such a threshold, then they can not be too distant from each other. Hence we can interpret such solutions as perturbations of wave packets with large wave number. 相似文献