Overall Yield Trends

FIGURE 12.2 Correlation between AE and VMR from radial hexagon analysis. 

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It is of interest to compare results derived from utilizing the classical aqueous interfacial (CAIS) with those derived from utilizing the bisethylenediamine copper (BEDC) system reported in references 9 and 17. The yield of modified product is higher for the CAIS systems but the general overall yield trend as the stan-nane is varied is similar, indicating that the overall reaction pathways are similar for the two systems (yield trends CAIS -triphenyl >dioctyl >dibutyl > diphenyl > dimethyl BEDC-triphenyl > dioctyl > dimethyl > dibutyl > diphenyl). These trends have been established over only a narrow set of reaction conditions and should be more fully developed before acceptance as overall yield trends. 

Overall yields and product distributions obtained in experiments using CH3CI, CH2CI2, and C2H5CI are shown in Table 3. The overall trends of reactivities obtained with various coinitiators at various... 

Figure 12.3 shows the trend between % overall yield and VMR obtained from the radial hexagon analysis based on 587 plans for compounds with multiple plans as noted in Chapter 13. Most plans gravitate to the lower left-hand comer of the plot. The four plans in the top right comer are as follows with the % overall yields given in parentheses (a) Roesler plan [20] for vanillin (70.0) ... 

For the aqueous solution systems, the trend in yield is generally Ti> Zr > Hf For the interfacial system there are no clear trends with respect to yield as a ftmction of the Group IVB metal. The lack of an overall generally trend for the interfacial system may be due to other factors being important, such as ability of the reactants to arrive at the surface and/or penetrate the interface. 

The overall yield is Hf > Ti > Zr for both aqueous solutions and interfacial systems. While the Ti > Zr portion can be rationalized using die HSAB approach, where both R-SH and R-S are considered soft bases, the overall trend is difficult to explain. Treating CP2MCI2 and Cp2M" as intermediate bases, we would predict that die order should be Ti > Zr > Hf Group IVB metallocenes are considered as hard bases. 

On the basis of the observed trends in aldehyde rate coefficients (see later in this chapter) we expect that abstraction from the aldehyde group accounts for a large fraction of the overall reaction. Vandenberk and Peeters (2003) found that the overall yield of H2O from the reaction is 100 10%, and that the formation of formic acid in an addition-elimination mechanism accoimts for less than 3%. 

Comparison of Figure 4.1.10a and b demonsfrafes fhaf despite the quantitative differences in fhe deduced values, bofh fhe extraction methods yield a similar trend in the range of equivalence ratios investigated. The overall activation energy is observed to peak close to the stoichiometric condition and decrease on both the lean and rich sides. In addition, the overall activation energy values for n-heptane/air mixtures are observed to be lower when compared with iso-octane/air mixtures for all equivalence ratios under consideration. This similarity of trend and the differences in absolute values using two different extraction methods are also observed in the numerical computations with the available detailed... 

The comparison of coronal and photospheric abundances in cool stars is a very important tool in the interpretation of the physics of the corona. Active stars show a very different pattern to that followed by low activity stars such as the Sun, being the First Ionization Potential (FIP) the main variable used to classify the elements. The overall solar corona shows the so-called FIP effect the elements with low FIP (<10 eV, like Ca, N, Mg, Fe or Si), are enhanced by a factor of 4, while elements with higher FIP (S, C, O, N, Ar, Ne) remain at photospheric levels. The physics that yields to this pattern is still a subject of debate. In the case of the active stars (see [2] for a review), the initial results seemed to point towards an opposite trend, the so called Inverse FIP effect , or the MAD effect (for Metal Abundance Depletion). In this case, the elements with low FIP have a substantial depletion when compared to the solar photosphere, while elements with high FIP have same levels (the ratio of Ne and Fe lines of similar temperature of formation in an X-ray spectrum shows very clearly this effect). However, most of the results reported to date lack from their respective photospheric counterparts, raising doubts on how real is the MAD effect. 

Column IV shows the product ratios in the presence of ultrasound and in the presence of pyridine. Overall there is the same trend with sonication, namely a slight shift from one-electron towards two-electron pathway, though here there is a higher yield of benzaldehyde derived by-products (approx. 16%). 

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