Search results for "Benzene"
showing 10 items of 1701 documents
The benefit of multipore zeolites: Catalytic behaviour of zeolites with intersecting channels of different sizes for alkylation reactions
2009
Abstract The catalytic behaviour of two multipore zeolites containing channels of different sizes, SSZ-33 (10 windows × 12 MR) and ITQ-22 (8 × 10 × 12 MR pores), for alkylation of benzene with ethanol and benzene with isopropanol or propylene, has been studied and compared to that of zeolites with intersecting channels of the same size, ZSM-5 (10 × 10 MR channels) and Beta (12 × 12 MR channels), which are industrially used for the above-mentioned process. For the alkylation of benzene with ethanol in gas phase, ITQ-22 behaves like the 10 MR ZSM-5 with respect to ethylbenzene selectivity, while the behaviour of SSZ-33 is close to that of a 12 MR zeolite such as Beta. For the alkylation of be…
Alkylation of Benzene with Short-Chain Olefins over MCM-22 Zeolite: Catalytic Behaviour and Kinetic Mechanism
2000
Abstract Benzene alkylation with ethene and propene has been carried out under liquid-phase reaction conditions over zeolites MCM-22, Beta, and ZSM-5. MCM-22 seems to be a good catalyst for benzene alkylation especially with propene, showing high activity and stability and good selectivity. Kinetic experiments show that alkylation with propene follows an Eley–Rideal type mechanism.
Valence Topological Charge-Transfer Indices for Dipole Moments
2003
Valence topological charge-transfer (CT) indices are applied to the calculation of dipole moments. The dipole moments calculated by algebraic and vector semisums of the CT indices are defined. The combination of the CT indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them with the dipole moment of the valence-isoelectronic series of benzene and styrene. Two CT indices, μ v e c (vector semisum of vertex-pair dipole moments) and μ V v e c (valence μ v e c ) are proposed. μ v e c and μ V v e c are important for the predicti…
NMR Study of Kraft Pulp Mill Waste and Natural Humic Substances
1988
High field proton NMR spectroscopy in DMSO-d6 solution is applied for structural analysis of main high molecular fractions of natural humus and waste lignin from kraft pulp mill. The spectra are similar in great part. Main differences appear in p-disubstituted benzene proton and -CH2 -CO-proton signals which are absent in spectrum of waste lignin obviously due to chlorination. A new observation of 51 Hz 1:1:1 triplet in both spectra is discussed.
Substituent effects on the stability of the four most stable tautomers of adenine and purine
2019
Substituent effects at the C2-, C8- and N-positions of adenine and purine in their four the most stable tautomers are studied by means of B97D3/aug-cc-pvdz computation applying substituents of varying electronic properties: NO2, CN, CHO, Cl, F, H, Me, OMe, OH and NH2. The substituent effect is characterized by the substituent effect stabilization energy (SESE) and substituent Hammett constant σ. For adenine, SESE is obtained with purine as the reference system. Additionally, for both adenine and purine, SESE characteristics are estimated with benzene, imidazole and amino-pyrimidine as reference systems, when possible, taking into account substitution in topologically equivalent positions. T…
A new pyrazolo pyrimidine derivative inhibitor of cyclooxygenase-2 with anti-angiogenic activity
2003
In a previous study, we reported a new pyrazolo pyrimidine derivative, N(4)-benzyl-N(6),N(6)-dimethyl-1-1(tert-butyl)-1H-pyrazolo[3,4-d]pyrimidine-6,4-diamine (DPP), which inhibited potently cyclooxygenase-2 activity in intact cell assays with minor activity against cyclooxygenase-1 (IC(50)=0.9 nM for cyclooxygenase-2 versus IC(50)=59.6 nM for cyclooxygenase-1). In the present work, this behaviour was confirmed in vivo by using the 24-h zymosan-injected mouse air pouch model (ID(50)=1.36 nM/pouch for prostaglandin E(2) level). We also studied the possible beneficial effect of DPP in the angiogenesis-dependent murine air pouch granuloma and rat paw carrageenan-induced hyperalgesia models. DP…
Crystal structure of 1-ferrocenyl-2-(4-methyl-benzo-yl)spiro-[11H-pyrrolidizine-3,11'-indeno[1,2-b]quinoxaline].
2014
In the title compound the four-fused-rings system is approximately planar and the pyrrolidine rings of the pyrrolidizine fragment adopt a twist conformation. In the crystal, molecules are linked by C—H⋯O hydrogen bonds and C—H⋯π interactions, forming double-chains parallel to the c axis.
A novel approach to predict aquatic toxicity from molecular structure
2008
The main aim of the study was to develop quantitative structure-activity relationship (QSAR) models for the prediction of aquatic toxicity using atom-based non-stochastic and stochastic linear indices. The used dataset consist of 392 benzene derivatives, separated into training and test sets, for which toxicity data to the ciliate Tetrahymena pyriformis were available. Using multiple linear regression, two statistically significant QSAR models were obtained with non-stochastic (R2=0.791 and s=0.344) and stochastic (R2=0.799 and s=0.343) linear indices. A leave-one-out (LOO) cross-validation procedure was carried out achieving values of q2=0.781 (scv=0.348) and q2=0.786 (scv=0.350), respecti…
Toward the Physical Interpretation of Inductive and Resonance Substituent Effects and Reexamination Based on Quantum Chemical Modeling
2017
An application of a charge of the substituent active region concept to 1-Y,4-X-disubstituted derivatives of bicyclo[2.2.2]octane (BCO) [where Y = NO2, COOH, OH, and NH2 and X = NMe2, NH2, OH, OMe, Me, H, F, Cl, CF3, CN, CHO, COMe, CONH2, COOH, NO2, and NO] provides a quantitative information on the inductive component of the substituent effect (SE). It is shown that the effect is highly additive but dependent on the kind of substituents. An application of the SE stabilization energy characteristics to 1,4-disubstituted derivatives of BCO and benzene allows the definition of inductive and resonance contributions to the overall SE. Good agreements with empirical approaches are found. All calc…
The Equilibrium Structure of Benzene
2000
The re structure of benzene is revised on the basis of high-level quantum chemical calculations at the CCSD(T)/cc-pVQZ level as well a reanalysis of the experimental rotational constants using computed vibrational corrections. A least-squares fit to empirically determined Be constants yields re(CC) = 1.3914 ± 0.0010 A and re(CH) = 1.0802 ± 0.0020 A; the latter distance is significantly shorter than the best previous estimate based on experimental data. Comparison of computed rg and rz distances with experiment as well as considerations of bond lengthening due to anharmonicity are consistent with the estimated re distance, indicating that the recommended structural parameters are very accura…