Juan Murgich

The areas of signals present in 12 consecutive frequency bins of the H nuclear magnetic resonance (NMR) spectra of different vacuum residues (VRs) were correlated with the yield of the deasphalting/demetallization process (DEMEX) under fixed and variable conditions (antisolvent/load ratio and rectification temperature). Prediction models for the demetallized oil (DMO) obtained under variable process conditions generated by partial least squares

An ab inito SCF-MO calculation of the electric field gradient (EFG) using a double zeta basis set with polarization is reported for N−3, HN3 NCN3, and H3CN3. A similar calculation using a Dunning set with polarization is also reported for N−3, HN3, and H3CN3. Excellent correlation was found between the calculated and the components obtained from gas phase microwave data. The calculation showed that the terminal N atom had a positive nuclear quadrupole coupling constant and its pincipal z axis was found to be perpendicular to the NNN direction in substituted azides. The changes in the charge distribution of HN3 and NCN3 obtained from the analysis of the atomic multipoles was shown to be in general agreement with the variations found in the N EFG components calculated for these azides. The 14N nuclear quadrupole resonance frequencies of the terminal and the first N atom of the azide group have been measured at 77 K for phenyl, benzyl, triphenylmethane, and tosyl azide. An analysis based on the Townes and Dailey approach of the measured NQR data showed that the terminal N atom have lost more σ than π orbital population. A similar analysis for the first N atom of azides showed strong inductive and resonance interactions with the substituents.

A combination of Molecular Mechanics and Density Functional Theory allowed the calculation of the charge distribution and the adsorption energy on the (001) surface of hematite (α-Fe 2 O 3 ) of a set of twelve molecules that represent fragments of resins and asphaltenes. The ...

Problems surrounding molecular aggregation, covalent molecular weight, and their experimental investigation in asphaltene chemistry are reviewed. Chromatographic, fluorescence spectroscopic, and mass spectroscopic (MS) methods for the investigation of these ...

Cl NQR frequencies for 2:2 salts of trichloroacetic acid (TCA) with 4-methylpyridine-N-oxide and 4-methylquinoline-N-oxide were measured at 77 K. Comparison of Cl frequencies for 2:1 and 2:2 salts shows that the crystal field makes a small contribution to the frequency shifts (FS) ...

The contributions of each localized orbital of the CN group and of the molecular remainder to the N electric field gradient (EFG) were calculated for nitriles with R = H, F, CH3, OH, NH2, CCH, COH, NO, CN and the E and Z forms of iminoacetonitrile. The changes in the EFG ...

A relationship between some of the critical points of the Laplacian of the charge density of the N valence shell and the electric field gradient (EFG) present at the nucleus of the three-coordinated N atom was found for the amine group in urea and some of its adducts and salts. The qzz component of the EFG was shown to be determined by two nonbonded charge distribution local maxima present below and above the molecular plane in the N valence shell. The asymmetry parameter of the EFG was found to be related also to this nonbonded charge concentration. The effect of increasing protonation in urea produced a decrease in the N nonbonded charge concentrations, an increase in bonded concentration along the N–H bond directions and complex fluctuations in the bonded concentration along the N–C bond. The combined effect of the additional H bonds involving the amine group of urea and of the O atom protonation on the N valence shell concentration, is also discussed.

The 14N NQR frequencies measured at 77 K for the amine group of the 1:1 salts of nitric acid with methylurea and 1,3‐ and 1,1‐dimethylurea and the phosphoric acid salt of 1,3‐dimethylurea are reported. The analysis of the NQR data showed that the N loses population from its π orbital. The decrease in π population is partially compensated by an increase in the population of the NC σ bonds. The loss of π population is enhanced when the H atoms of the amine group are substituted by electron‐donating groups such as CH3.

The 14N NQR frequencies of urea complexes with H2O2 (1:1), NH4Cl (1:1), oxalic (2:1), phosphoric (1:1), and nitric acid (1:1) at 77 °K are reported. The analysis of the NQR data indicates that the population of the N nonbonding orbital decreases and that the population of the s N–H and N–C bonds increases as the degree of protonation of the O atom of urea increases. These changes are consistent with a larger weight of structures like C = N+H2 as the protonation increases. The NQR results are in agreement with those obtained from a CNDO/2 calculation for the uronioum ion [Yu. A. Panteleev and A. A. Lipovskii, Zhu. Struk. Khim. 17, 2 (1976)].

ABSTRACT The volatile aromatic fraction (240 °C and 10–3 Torr pressure) of Athabasca bitumen was separated via thin-layer chromatography (TLC) (Ag+/SiO2), followed by alumina column chromatography, into 13 mono-, di-, and triaromatic subfractions, each of which was subjected to field ionization mass spectrometry (FIMS) analyses. Altogether, close to 6000 constituent molecules, ranging in molecular weight from 200 to 800 Da, have been observed, including the partially and fully aromatized, ring-opened, and truncated derivatives of essentially all of the saturated biomarkers detected here or earlier in the saturated fraction of this bitumen. All molecules detected were of aromatic character, with the exception of a complex suite of cyclic terpenoid (and steroid) sulfides, having adsorptive properties similar to those of the triaromatic hydrocarbons. In several cases, the FIMS analyses were supplemented by conventional biomarker analyses and a novel biomarker analysis, employing basic aqueous extraction of the whole oil sands. The high-molecular-weight portion (MW > 482 Da) of each subfraction isolated (which usually does not show up in conventional biomarker analyses) varies in concentration from a few to about 10 wt %. This fraction may arise from processes analogous to the combination reactions occurring in the addition of biomarker molecules to asphaltene by C–C, C–S–C, and C–O–C covalent bond formation. In the present system (with the exception of the cyclic sulfides), only C–C bond additions can be operative.

It is shown by sequential reprecipitation that both n-C 5 and n-C 7 Athabasca asphaltene contain significant amounts of precipitant solubles, comprising resins and low-molecular-weight asphaltene-like substances in about the same percentage amounts relative to the ...

ABSTRACT The 14N NQR spectra of quinoline, 2-chloroquinoline, 1,5-naphthyridine and its hydrated form, 1,8-naphthyridine, 1,3-benzodiazine, 2,3-benzodiazine, 1,2-benzodiazine, and 1,4-benzodiazine were obtained at 77 K. Also the N electric field gradient EFG for quinolines, naphthyridines, and benzodiazines was calculated using an ab initio method with a 6-31G* set. The effect of an additional ring and the substitution of a neighboring C by a N atom on the N EFG was interpreted by means of the topology of the charge distribution of the corresponding monocyclic azines used as model compounds.

The 14 N NQR spectra of H bonded complexes of 1,4 diazabicyclo [2,2,2] octane, also known as triethylenediamine (TED), with phenol (1:2), p-chlorophenol (1:2), p-nitrophenol (1:2), hydroquinone (1:1), resorcinol (1:1) and thiourea (1:2) were observed at 77 K. The 14 N frequency shifts ...

The temperature dependence of the 14N nuclear quadrupole resonance (NQR) spectrum of K-TCNQ was measured from 77 to 300 K. The NQR frequency shifts with temperature can be explained by considering the effects of the thermal averaging of the quadrupole parameters and the rearrangement of the TCNQ− and K+ stacks. The 14N NQR data are consistent with the observed Peierls transition found for K-TCNQ.

In order to determine the forces acting in the asphaltene and resin molecular aggregates, an analysis of the origin of the intermolecular interactions in organic molecules was made. The results showed that the forces present in the aggregates of asphaltenes and resins were only ...

An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Areas of resonance signals present in 12 frequency bins of the 1H NMR spectra of the vacuum residues of five Colombian crudes and a blend were correlated with their SARA components and some physicochemical properties. The residues studied were obtained ...

Journal of Molecular Structure (Theochem), 307 (1994) 1-8 0166-1280/94/S07.00 1994 - Elsevier Science BV All rights reserved Ab initio study of the molecular electrostatic potential of monocyclic and bicyclic azines Humberto J. Soscun M^'0, Yosslen Aray^, Juan Murgich15, Alan ...

The contributions of each localized orbital of the CN group and of the molecular remainder to the N electric field gradient (EFG) were calculated for nitriles with R = H, F, CH3, OH, NH2, CCH, COH, NO, CN and the E and Z forms of iminoacetonitrile. The changes in the EFG ...

ABSTRACT It was found that the topology of the Laplacian of the molecular charge distribution can be used in the evaluation of the reactivity of model active sites such as those involved in the gas phase H abstraction from CH4 by MgO and LiO molecules. The improvement of the catalytic activity of the surfaces of these solid oxides based in this result is also discussed.

A relationship between some of the critical points of the Laplacian of the charge density of the N valence shell and the electric field gradient (EFG) present at the nucleus of the three‐coordinated N atom was found for the amine group in urea and some of its adducts and salts. The q ...

The previously reported 14 N NQR spectrum of the CN groups of Ba [Fe (CN) 5 NO] · 3H 2 O (BNP) was shown to also contain lines of Na 2 [Fe (CN) 5 NO] · 2H 2 O used in the preparation of BNP. The number of NQR lines and their relative intensities in BNP confirmed that it ...