Search results for "Roca"
showing 10 items of 1893 documents
Industrial applications of the aggregation of block copolymers in supercritical CO 2 : a SANS study
2002
Industrial applications of supercritical carbon dioxide (scCO2) rely upon the rather selective and easily adjustable solvent ability of CO2. CO2 near the critical point is a poor solvent for high molecular weight (HMW) hydrocarbon polymers, while it is a very good solvent for amorphous fluorinated polymers. By increasing the pressure, CO2 becomes a good solvent even for HMW hydrogenated chains. Specially engineered amphiphilic di-block copolymers, with CO2-philic and CO2-phobic portions, are expected to undergo trough a monomer–aggregate transition when the solvent density of the scCO2 changes. Here small-angle neutron scattering (SANS) results are reported for a block copolymer dissolved i…
Tandem asymmetric Michael reaction-intramolecular Michael addition. An easy entry to chiral fluorinated 1,4-dihydropyridines.
2010
A novel one-pot tandem asymmetric Hantzsch-type process has been employed to generate fluorinated 1,4-dihydropyridines (1,4-DHPs) as single diastereoisomers. It involves the condensation of (R)-(+)-allyl p-tolyl sulfoxide, fluorinated nitriles, and alkyl propiolates, giving access to a new family of enantiomerically pure fluorine-containing 1,4-DHPs.
Asymmetric synthesis of fluorinated amino macrolactones through ring-closing metathesis
2007
The synthesis of new chiral fluorinated amino and azamacrolactones of types 1 and 2 is described. A ring-closing metathesis (RCM) reaction constitutes the key step in this methodology, which uses fluorinated amino alcohols 7 as starting materials. The influence of the CF2 group, which is located in the alpha-position relative to the carbon bearing the amino group, on the efficiency of the RCM reaction is noteworthy. This method allows for the preparation of the desired fluorinated macrolactones in excellent yields.
Small hydrocarbon cyclophanes: Synthesis, X-ray analysis and molecular modelling
2002
Small hydrocarbon cyclophanes, such as [2.2.0]m,m,m-cyclophane (20) and [2.2.0]p,m,m-cyclophane (21), are strained analogues of the well-known π-prismand [2.2.2]p,p,p-cyclophane (1). The synthetic route to these molecules is based on well-established cyclophane methodology which offers a general access to a whole family of hydrocarbon cyclophanes. Single crystal X-ray analysis and molecular modelling showed that the reduction of the ring size from 18-membered (1) to 14-membered (21) or 13-membered (20) has a substantial effect on the size and the shape of the cyclophane’s cavity, thus blocking its ability to complex Ag+ ions. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
Formation, phase composition, and transformations of Langmuir-Blodgett multi- and monolayers containing Fe
1992
Mono- and multilayers of ferric stearate were formed by the Langmuir-Blodgett technique. Thermodesorption of the hydrocarbon chains results in well defined thin oxidic films. Their reduction to Fe2+ and α-Fe was followed by conversion electron Mossbauer spectroscopy. Resonance lines can be observed even if the Fe coverage is less than one monolayer.
Enhanced Sieving of C2‐Hydrocarbon from Methane by Fluoro‐Functionalization of In‐MOF with Robust Stability
2021
Developing efficient adsorbent materials is crucial for adsorption and separation to realize the purification of energy source and raw chemicals. Here, we report a novel and robust 3D In-based MOF built up with fluorine-functionalized ligands, QMOF-2F, with improved separation properties of C2-light hydrocarbons over methane at room temperature respect isoreticular non-fluorinated MOF. QMOF-2F shows a remarkable chemical stability in different solvents, including water, and pH (2-12). DFT calculations support the key role of fluorine-functionalization on the improved performance of QMOF-2F.
Vibronic structure in triatomic molecules : The hydrocarbon flame bands of the formyl radical (HCO). A theoretical study
1998
A theoretical study of the vibrational structure of the math 2A′ ground and math 2A′ excited states of the formyl radical, HCO, and its deuterated form, DCO, has been performed. The potential energy surfaces have been computed by means of a multiconfigurational perturbative method, CASPT2. The computed geometries and the harmonic and anharmonic frequencies are successfully compared to the available experimental information. The vibrational intensities of the transition math 2A′↔math 2A′ have been computed both for absorption and emission. The results lead to accurate determinations of several structural parameters and some reassignments of the vibrational transitions of the so-called hydroc…
Stabilisation of LDPE cross-linked in the presence of peroxides III. Mass spectrometric study of chemical changes taking place in the n-octadecane–di…
2000
Abstract An attempt was made to identify the products of the reaction between dicumyl peroxide and Irganox 1081, carried out in n -octadecane (saturated hydrocarbon), in conditions of fast decomposition of the peroxide (180°C, 5 min). Mass spectrometry (MS) was employed to find m/z values of molecular and fragment ions in analyses of the components ( n -octadecane, dicumyl peroxide, Irganox 1081) and of the following systems: n -octadecane–dicumyl peroxide, n -octadecane–Irganox 1081 and n -octadecane–dicumyl peroxide–Irganox 1081, after holding them at a temperature of 180°C for 5 min. The tendency of sulphur in Irganox 1081 to oxidise, specifically in the presence of dicumyl peroxide, was…
Calculation of the Phase Behavior of Lipids
1998
The self-assembly of monoacyl lipids in solution is studied employing a model in which the lipid's hydrocarbon tail is described within the Rotational Isomeric State framework and is attached to a simple hydrophilic head. Mean-field theory is employed, and the necessary partition function of a single lipid is obtained via a partial enumeration over a large sample of molecular conformations. The influence of the lipid architecture on the transition between the lamellar and inverted-hexagonal phases is calculated, and qualitative agreement with experiment is found.
Electrical conductivity and permittivity of water-AOT-n-heptane microemulsions
1995
Measurements of the electrical conductivity and of the complex permittivity of water-sodium bis(2-ethylhexyl) sulfosuccinate (AOT)-n-heptane microemulsions are reported. The experimental results are rationalized in terms of a hopping mechanism of AOT anions within clusters of reversed micelles. The dependence of the hopping rate and of the cluster dimensions upon the ratio [water]/[AOT] and temperature is discussed.