For partially resolved

Partial Resolution and Absolute Configurations. Partial resolution of the Co(admh)n(acac)g n complexes was effected by column chromatography on D-(+)-lactose. Co(admh)(acac)2 was resolved partially at room temperature using a 230-cm column that we have employed previously for partial resolution of metal g-diketonates (10). However, this procedure did not work for the bis- and tris-admh complexes. The bis and tris complexes were resolved partially, with much greater difficulty, by a low-temperature procedure that employed D-(+)-lactose on alumina as the adsorbent, isopentane-ether as the eluent, and temperatures of-95 to-125°C. After chromatography, the eluent was evaporated and the enantiomer in excess was concentrated by extracting the solid with chlorodifluoromethane at -120°C. The values of - er for the Co(admh)n(acac)3 n complexes (Table IV) are very small compared with - er for partially resolved Co(acac)g (17), indicating that resolution was incomplete in all cases. 

Figure 5. Absorption spectrum, CD, and optical rotatory dispersion for partially resolved A-(—)Sie-Co(admh)(acac)2 in absolute ethanol first-eluted fraction from...

Doucet et described the determination of isotope ratios using LIBS in air at atmospheric pressure for partially resolved uranium-235-uranium-238 and hydrogen-deuterium isotope shift lines. A PLSl regression model could accurately predict the isotopic ratio under conditions where the application of traditional univariate approaches for hydrogen and uranium would not be achievable. 

When partially resolved samples of 5-hydroxymethylpyrrolidin-2-one are allowed to react with benzaldehyde in the presence of an acid catalyst, two products, A (C12H13NO2) and B (C24H26N2O4), are formed. The ration A B depends on the enantiomeric purity of the starting material. When the starting material is optically pure, only A is formed. When it is racemic, only B is formed. Partially resolved material gives both A and B. The more nearly it is enantiomerically pure, the less B is formed. The products A is optically active but B is achiral. Develop an explanation for these observations, including structures for A and B. 

Another error can arise when two partially resolved peaks are asymmetrical, e.g., the rear half of the peak is broader the front half. In such a situation, it is clear that there can be two sources of error, which are depicted in Figure 4. Firstly, the retention times, as measured from the peak envelope, will not be accurate. Secondly, because the peaks are asymmetrical (and most LC peaks tend to be asymmetrical to the extent shown in the Figure 4), the second peak appears higher. This can incorrectly imply that the second solute is present at a higher concentration in the mixture than the first. It follows that it is important to know the value of the specific separation ratio above which accurate measurements can still be made on the peak maxima of the individual peaks. The apparent peak separation ratio, relative to the actual peak separation ratio for columns of different efficiency, are shown in Figure 5. The data has been obtained from theoretical equations. 

Figure 13.22 shows the resolution of the surfactants Tween 80 and SPAN. The high resolution obtained will even allow the individual unreacted ethylene oxide oligomers to be monitored. Figure 13.23 details the resolution of many species in both new and aged cooking oil. Perhaps the most unique high resolution low molecular weight SEC separation we have been able to obtain is shown in Fig. 13.24. Using 1,2,4-trichlorobenzene as the mobile phase at 145°C with a six column 500-A set in series, we were able to resolve Cg, C, Cy, Cg, C9, Cio, and so on hydrocarbons, a separation by size of only a methylene group. Individual ethylene groups were at least partially resolved out to Cjg. This type of separation should be ideal for complex wax analysis.

Cyclodextrins, toroidal molecules composed of 6, 7 and 8 D-glucose units, are now commercially available at reasonable cost. They form inclusion compounds with a variety of molecules and often differentially include sulfoxide enantiomers29,30. This property has been used to partially resolve some benzyl alkyl, phenyl alkyl and p-tolyl alkyl sulfoxides. The enantiomeric purities after one inclusion process ranged from 1.1 % for t-butyl p-tolyl sulfoxide to 14.5% for benzyl r-butyl sulfoxide. Repeating the process on methyl p-tolyl sulfoxide (10) increased its enantiomeric purity from 8.1% to 11.4% four recrystallizations raised the value to 71.5%. The use of cyclodextrins in asymmetric oxidations is discussed in Section II.C.l and in the resolution of sulfmate esters in Section II.B.l. 

It is well known that spontaneous resolution of a racemate may occur upon crystallization if a chiral molecule crystallizes as a conglomerate. With regard to sulphoxides, this phenomenon was observed for the first time in the case of methyl p-tolyl sulphoxide269. The optical rotation of a partially resolved sulphoxide (via /J-cyclodextrin inclusion complexes) was found to increase from [a]589 = + 11.5° (e.e. 8.1%) to [a]589 = +100.8 (e.e. 71.5%) after four fractional crystallizations from light petroleum ether. Later on, few optically active ketosulphoxides of low optical purity were converted into the pure enantiomers by fractional crystallization from ethyl ether-hexane270. This resolution by crystallization was also successful for racemic benzyl p-tolyl sulphoxide and t-butyl phenyl sulphoxide271. 

Chiral Recognition. The use of chiral hosts to form diastereomeric inclusion compounds was mentioned above. But in some cases it is possible for a host to form an inclusion compound with one enantiomer of a racemic guest, but not the other. This is caUed chiral recognition. One enantiomer fits into the chiral host cavity, the other does not. More often, both diastereomers are formed, but one forms more rapidly than the other, so that if the guest is removed it is already partially resolved (this is a form of kinetic resolution, see category 6). An example is use of the chiral crown ether (53) partially to resolve the racemic amine salt (54). " When an aqueous solution of 54 was... 

An advantage of the mass spectrometer as a detector is that it may allow differentiation of compounds with similar retention characteristics or may allow the identification and/or quantitative determination of components that are only partially resolved chromatographicaUy, or even those that are totally unresolved. This may reduce the time required for method development and is discussed in more detail in Chapter 3. 

The great advantage of the mass spectrometer is its abihty to use mass, more accurately the mass-to-charge ratio, as a discriminating feature. In contrast to, for example, the UV detector, which gives rise to broad signals with little selectivity, the ions in the mass spectrum of a particular analyte are often characteristic of that analyte. Under these conditions, discrete signals, which may be measured accurately and precisely, may be obtained from each analyte when they are only partially resolved or even completely umesolved from the other compounds present. 

Already partially resolved methyl-1-naphthylphenylgermanium hydride ([otp°° + 10) could also be separated on column A into two fractions characterized by [a] g5 = + 80 and —42 respectively. Partial resolution could even be obtained for the configuration-ally less stable methyl-1 -naphthylphenylgermanium chloride if the elution was carried out with diethyl ether 53), which is much less nucleophilic towards germanium than methanol, which causes the racemization of this compound. 

C NMR of linear cross-linked PS. The proton decoupled 13C NMR spectra of linear and 1% cross-linked PS at 75 MHz in chloroform are illustrated in Figure 3. These spectra are similar to those for linear and cross-linked chloromethylated PS previously reported at lower field (14), although we have been able to resolve more structure in tHe" aliphatic and aromatic regions here. The quarternary and methylene carbon resonances at about 146 ppm and between 40 and 50 ppm respectively, are the most strongly affected by stereochemistry (20). The ortho and meta resonances at 128.4 ppm show partially resolved structure in the linear PS, as does the para carbon at 126.1 ppm. The methine resonance at... 

So we are still left with two models of the stereochemistry of DNA alkylated by a PAH diol epoxide the PAH either lies in a groove of DNA or else tries to intercalate between the bass of DNA. Since it is covalently bonded to a base it must cause considerable distortion if it tries to lie between the bases. However, the stacking observed in the crystalline state seems to argue for partial intercalation. We will need crystal structures of at least one appropriately alkylated polynucleotide before this problem can be resolved. And when this is done it will be just the beginning of the answer to the problem of alkylation of DNA by activated carcinogens. The subsequent question is, what is the lesion in DNA that is important in carcinogenesis, and then what does it cause to happen so that tumor formation is initiated ... 

The implication of these results is that deposition of, for example, R( +)-crystals on to the racemic films provides a nucleation site for R( + ) -molecules in the film, leaving behind a partially resolved film of predominantly S( — )-molecules. Deposition of S( — (-crystals should, alternatively, leave behind a film composed predominantly of R( + )-molecules. This model is supported by the ESP data obtained on the clean acidic surface, where the free energy of enantiomer crystals appears to be lower compared with liquid-like film states than that of the racemic crystals. 

Fig. 3. (a) Partially resolved nuclear hyperfine structure in the p.SR spectrum for Mu in GaAs in an applied field of 0.3 T. The structure occurs in the line corresponding to 0 = 90° and Ms = —1/2. (b) Theoretical frequency spectrum obtained by exact diagonalization of the spin Hamiltonian using the nuclear hyperfine and electric quadrupole parameters in Table I for the nearest-neighbor Ga and As on the Mu symmetry axis. Both Ga isotopes, 69Ga and 71Ga, were taken into account. From Kiefl et al. (1987). 

As early GC peaks elute in a few seconds or less, rapid scanning of the mass range of interest is necessary. Fast scanning also allows partially resolved GC peaks to be sampled several times,peak slicing, to facilitate identification of the individual components (Figure 12.5) provided that the dead volume of the interface is small compared to peak volumes. For the speedy interpretation of spectral data from complex chromatograms a... 

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