Search results for " Methods"
showing 10 items of 4102 documents
Crystal structure and reactivity of 2-chloro-3,5-dinitrothiophene and of 2-phenylsulphonyl-3,5-dinitrothiophene with nucleophiles
1988
The geometry obtained by a crystal structure determination of the title compounds, as compared with that of the analogous benzene derivatives, along with results of ab initio calculations, is used to interpret the different SNAr reactivities in some thiophene and benzene compounds. The smaller rotation of the nitro groups with respect to the aromatic rings observed in thiophene derivatives should be considered a relevant factor in the higher reactivity in the thiophene series.
Potential energy surface for the decomposition of mandelic acid
1997
Abstract The decomposition of mandelic acid has been studied by ab initio calculations at the MP2/6-31G ∗∗ level. Three competitive reaction pathways have been characterized, two are stepwise processes with the formation of an α-lactone intermediate, achieved by the nucleophilic attack of either the carbonylic oxygen atom (mechanism A) or the hydroxylic oxygen atom (mechanism B) of the carboxyl group, followed by a ring opening; the third pathway (mechanism C) is a one-step process. The calculated rate coefficient agrees with experimental data. The decomposition is energetically favourable along mechanism A.
Interpretation of the electronic absorption spectrum of free base porphin by using multiconfigurational second-order perturbation theory
1998
Abstract Multiconfigurational second-order perturbation (CASPT2) calculations have been performed on the low-lying optically allowed valence excited states of the free base porphin molecule in order to assign the four lowest bands of the spectrum. The low-lying triplet states have also been characterized. A basis set of the atomic natural orbital type of split-valence plus polarization quality for first-row atoms has been employed. Polarization functions are important for an accurate description of the transitions. These CASPT2 results provide a consistent picture of the experimental spectrum. Each band of the spectrum up to 4.5 eV is composed of a pair of states, which become degenerate in…
On the vertical excitation energy of cyclopentadiene
2004
The vertical excitation energy for the lowest valence pi--pi(*) transition of cyclopentadiene is investigated. Using a combination of high-level theoretical methods and spectroscopic simulations, the vertical separation at the ground state geometry is estimated to be 5.43+/-0.05 eV. This value is intermediate between those calculated with coupled-cluster and multireference perturbation theory methods and is about 0.13 eV higher than the observed maximum in the absorption profile.
Tricks and Tracks in the Identification and Quantification of Endocannabinoids
2013
Abstract The endocannabinoid system serves pivotal roles in a diverse range of physiological and pathophysiological states, including behavior, pain, schizophrenia, obesity, Alzheimer disease, multiple sclerosis and cardiovascular disease. A number of endocannabinoids (eCBs) and their receptors have been characterised and identified in a plethora of biological matrices. The eCBs include N-arachidonoyl ethanolamine (anandamide), 2-arachidonoyl glycerol, 2-arachidonoyl glyceryl ether (noladin ether), O-arachidonoyl ethanolamine (virodhamine) and N-arachidonoyl dopamine. Advanced targeted mass spectrometry methods, particularly the selected reaction monitoring, has facilitated sensitive quanti…
Fate of several hydroxyalkyl isoprene radicals: Formation of hydroxycarbonyl compounds
2005
Abstract The fate of two hydroxyalkyl radicals derived from the oxidation of isoprene with OH radical, resulting in the formation of two hydroxycarbonyls, was investigated by means of theoretical quantum chemistry methods. All the stationary points were optimised at the UMP2/6-31G(d) level, and high-level ab initio calculations were performed at the QCISD(T)/6-31G(d) level of computation upon MP2 optimised structures in order to refine the energy of the molecules characterised. Our results show that the reaction of hydroxyalkyl radicals with O 2 is a very favoured pathway that explains the formation of the two hydroxycarbonyls optimised.
Energy and environmental impact of an anaerobic membrane bioreactor (AnMBR) demonstration plant treating urban wastewater
2020
Abstract In order to assess the environmental feasibility of anaerobic membrane bioreactor (AnMBR) technology for urban wastewater (UWW) treatment at ambient temperature, a demonstration plant was operated within the LIFE MEMORY project ( http://www.life-memory.eu/en/ ). This plant incorporates full-scale hollow-fiber membrane modules and was fed with the effluent from the pre-treatment of the “Alcazar de San Juan” WWTP (Alcazar de San Juan, Ciudad Real, Spain). Because of the dimensions of this plant, the system can be regarded as a previous step to the scale-up of AnMBR technology for full-scale UWW treatment. High-energy recovery potentials were achieved treating medium-/high-loaded UWW …
Towards a converged barrier height for the entrance channel transition state of the N(2D)+CH4 reaction and its implication for the chemistry in Titan…
2011
Abstract The N( 2 D) + CH 4 reaction appears to be a key reaction for the chemistry of Titan’s atmosphere, opening the door to nitrile formation as recently observed by the Cassini–Huygens mission. Faced to the controversy concerning the existence or not of a potential barrier for this reaction, we have carried out accurate ab initio calculations by means of multi-state multi-reference configuration interaction (MS-MR-SDCI) method. These calculations have been partially corrected for the size-consistency errors (SCE) by Davidson, Pople or AQCC corrections. We suggest a barrier height of 3.86 ± 0.84 kJ/mol, including ZPE, for the entrance transition state, in good agreement with the experime…
Excited State N−H Tautomer Selectivity in the Singlet Energy Transfer of a Zinc(II)-Porphyrin-Truxene-Corrole Assembly
2017
International audience; An original corrole-containing polyad for S-1 energy transfer, in which one zinc(II)-porphyrin donor is linked to two free-base corrole acceptors by a truxene linker, is reported. This polyad exhibits a rapid zinc(II)-porphyrin*free-base corrole transfer (4.83x10(10)s(-1); 298K), even faster than the tautomerization in the excited state processes taking advantage of the good electronic communication provided by the truxene bridge. Importantly, the energy transfer process shows approximately 3-fold selectivity for one corrole N-H tautomer over the other even at low temperature (77K). This selectivity is due to the difference in the J-integral being effective in both t…
Formation of meso-1,2-Bis(dimethylamino)-1,2-diphenylethane by Oxidative C-C Coupling Reaction
2005
The title compound was obtained from the reaction of N,N-dimethylbenzylamine with n-butyl lithium and sulfur in tetrahydrofuran at room temperature. Its molecular structure was investigated by means of single crystal X-ray diffraction and quantum chemical DFT methods. The formation of meso-1,2-bis(dimethylamino)-1,2-diphenylethane is likely to be due to an unusual α-deprotonation of N,N-dimethylbenzylamine, instead of the well known ortho-lithiation, with a subsequent oxidative C-C coupling of the anions. Ab initio calculations of the corresponding α- and o-deprotonated anions of N,N-dimethylbenzylamine showed the former to be more stable than the latter, due to delocalisation of the negati…