Mixtures of model compounds

A shift of stretching vibrations vc=0 from 1590 to 1640 cm-1 is observed in the mixture of model compounds which points to intermolecular coordination interactions. 

A Sulfur K Edge X-ray Absorption Near Edge Structure (XANES) Spectroscopy method has been developed for the direct determination and quantification of the forms of organically bound sulfur in nonvolatile petroleum and coal samples. XANES spectra were taken of a number of model compounds, mixtures of model compounds, heavy petroleum and coal samples. Analysis of the third derivatives of these spectra allowed approximate quantification of the sulfidic and thiophenic components of the model mixtures and of heavy petroleum and coal samples. These results are compared with those obtained by X-ray Photoelectron Spectroscopy (XPS). 

Chlorination of Mixtures of Model Compounds. A laboratory chlorination technique that was compatible with the XAD concentration technique and the mutagenicity assay was developed. Thus, a relatively long chlorine contact time in comparison to sampling time was used to complete the reaction before sampling and to achieve a low residual... 

The concentrations of amino acids in the buffered aqueous solutions (pH 6.2) were selected to give a total organic carbon content of 1-3 mg/L, and chlorination conditions were as described for the chlorination of mixtures of model compounds. The chlorinated solutions were concentrated by XAD-2 adsorption/ethyl ether elution, tested for mutagenicity, and analyzed by GC-MS. 

The product yields from mixtures of model compounds were predicted to within +2% from those of the constituents. 

Approximate uncertainty based on measurements on mixtures of model compounds... 

Carbon-13 NMR Spectroscopy. High resolution 13C NMR spectra of maltenes, bitumen, and liquid products taken up in a 1 2 mixture of CDC13 were obtained on a Varian XL-100-15 FT spectrometer equipped with a V-4412 probe and a 2.5 mega word disc. A pulse angle of 45° and a repetition period of 60 s were selected to avoid saturation of any nonprotonated carbons. Gated decoupling was also employed to suppress NOE effects in the line intensities. These precautions have been shown for mixtures of model compounds to minimize error in integrated line intensities to less than 10% (3). 

Large aluminum oxide (100-200 g Al203,Merck Aluminiumoxid 90,70-230 mesh ASTM) columns and carbon (Alltech, SK 4, 80/100) columns with he-xane/dichloromethane and toluene as eluents have been used to fractionate the mixtures of model compounds [29,30]. Activated carbon chromatography managed to remove most starting compounds and some sulfur from the synthesis mixtures. The mixtures of PCDTs and PCTAs obtained were further fractionated and purified by reversed-phase HPLC with a Silas orb C8 SPH (ELSICO) and a Spherisorb S5 ODS-2 column. Acetonitrilerwater (65 35) at a flow rate of 1 ml/min was used as eluent and the UV detector adjusted to 254 nm [30,32]. 

Figure 8 H NMR spectra of (A) desilylated product of completely soluble polymer hb-Pl (sample taken from Table 1, entry 4), (B) desilylated product of partially soluble polymer hb-Pl (sample taken from Table 1, entry 5), (C) mixture of model compounds 15 (Fig. 7), (D) pure isomer 1,3,5-15, and (E) pure isomer 1,2,4-15.

Buckles et al. suggested tentative structural assignments for 53a and 53b and their respective benzamido acids on the basis of ultraviolet spectral data and by comparison of physical properties with those of model compounds. They pointed out that it is not possible to establish structural relationships from configurations of the diastereomeric 2-benzamido-3-methoxy-3-phenylpropionic acids (54), each of which, on treatment with acetic anhydride, give mixtures of the azlactones. Similar observations have been made by others. ... 

The formation of compound (1) has been established under well-defined laboratory conditions in such reaction mixtures [15,26-35]. Comparison of nuclear magnetic resonance (NMR) spectra of model compounds prepared by Bakker and Cerfontain [29] with those of the reaction mixture has also clearly shown the presence of (1). p-Sultones (1) have also been identified in commercial scale equipment under less well-defined conditions [21-24]. 

Chemical shift (p.p.m.) of model compounds in H20 relative to internal 1,4-dioxane (67.86 p.p.m.). Chemical shifts for these compounds are given at pH 5.5-7.5. Estimated precision for the chemical shifts is 0.05 p.p.m.h See Refs. 82 and 83. See Ref. 20.d These assignments may have to be interchanged. See Ref. 21 numbers in the brackets below the given chemical shift values refer to those published in Ref. 86. f See Ref. 19. The chemical shift for the -anomeric carbon atom was found to be 100.6 p.p.m. and was determined from an anomeric mixture of this compound. The existence of the a-Man — Ser unit was confirmed by the l]CH value (169 Hz) obtained for this compound. See Ref. 84. 

In the spectra of model compounds such as succinic anhydride (SA), tri-n-butyl-stannyl 2-methylpropanoate (TBMP) and their mixtures and a copolymer of tri-... 

A study of the simultaneous reaction of model compounds typically present in VGO, led to the proposal of approximated networks. The mixture was composed of DBT,... 

Preparation of model compounds and polyurethanes. A procedure for the preparation of the non-silicon containing monocarbamate and biscarbamate models has been reported previously (8). In order to obtain the silicon containing model compound, 5.0 g of bis(4-aminophenyl) dimethyl silane [synthesized according to Pratt, et.al (9)] was added to 7.0 g ethyl chloroformate at room temperature. A salt immediately formed. The mixture was refluxed for 15 min. The solution was then cooled, vacuum filtered, and recrystallized from ethanol to yield 1.0 g of a white powder MP 162-3 °C Anal. c20H26°4N2Si Calc. C, 62.17 H, 6.70 N, 7.23 Found C, 62.01 H, 6.79 N, 7.42. 

The results of theoretical calculation using both general rate and transport-dispersive models were in good agreement with the overloaded band profiles determined experimentally, therefore, the method has been found to be suitable for the prediction of band profiles [88], Natural pigments were generally used as a complicated mixture of various compounds with chromophore substructure. Their separation by preparative RP-HPLC is not necessary, and the application of preparative RP-HPLC for the purification of one or more pigment fractions is not expected in the near future. 

Finally, we recently found that TIQDT is also suited for estimating the potential hazards associated with mixtures of TGFDs [Thienpont et al., manuscript in preparation]. We have found that mixtures of eight compounds with both similar MoA act according to the concentration-addition model (Fig. 6). Moreover, a mixture of these eight compounds at their NOEC inhibited almost completely... 

The separation of a mixture of aromatic compounds (benzene, naphthalene, anthracene, chrysenes, and benz(a)pyrene) at 31 bar is shown in Figure 3. This chromatogram was obtained with a Perkin Elmer Model 250 ultraviolet detector with the high-pressure cell placed after the cooling heat exchanger and before the flow control valve. A similar chromatogram is obtained with an Isco Model UAA with a 10 mm micro cell placed after the flow control valve. 

There are several potential sources of error. Both methods of analysis use a binary model mixture, composed of sulfidic and thiophenic components. Thickness effects in the XANES of these model systems would alter the calibrations. There may be contributions from species not adequately represented by a simple dibenzothiophene-dibenzylsulfide model. While the XPS data are represented by 163.3 eV and 164.1 eV components, the model compound data base is as yet limited and not sufficient for a definitive interpretation in terms of alkyl sulfide and thiophenic forms. Examination by both XPS and XANES of a wider variety of model compounds and multiple component model compound mixtures will better define the sulfur species represented by these quantification methods. 

The first group consists of the model dependent approach in which mathematical models are generated for every formulation property of interest as a function of the composition of the mixture of the compounding substances and possibly process variables [23]. This method is called the simultaneous approach. The settings of all the variables (mixture components and/or process variables) in the employed model have to be... 

One of the major problems in studying polymers quantitatively is the absence of model compounds for the purpose of calibration. A method of obtaining spectra of the components of a mixture spectra is based on obtaining the ratio of absorbances. This method was first used by Hirschfeld 851 for mixtures of components differing in relative concentration. This approach was later generalized but is limited to a rather... 

By AEDA the four odorants shown in Figure 9 were detected with the highest FD-factors in dill herb [33], A mixture of these compounds, dissolved in water at the same concentration ratios occurring in the herb (Table 16) very much resembled the typical odor of the dill herb. If (S)-a-phellandrene or the dill ether (B and A Fig. 9), respectively, were omitted, the mixture lost its typical odor note. On the contrary, omission of myristicin and methyl 3-methylbutanoate (D and C Fig. 9) did not significantly influence the overall dill herb aroma of the model mixture [33, 66], The data indicated that (S)-a-phellandrene and the dill ether are the character impact compounds of the dill herb. Since, on the basis of AEDA or calculation of OAVs further odorants have been shown to contribute to the dill herb flavor [33, 66], the results of the simulation experiments revealed that obviously the two monoterpenes are able to mask the flavor contributions of these compounds. 

Humic Materials. Adsorption studies of model compounds have been primarily directed toward single compound classes rather than mixtures, even simple... 

---