Carbon functions, determination

This review will restrict itself to boron-carbon multiple bonding in carbon-rich systems, as encountered in organic chemistry, and leave the clusters of carboranes rich in boron to the proper purview of the inorganic chemist. Insofar as such three-dimensional clusters are considered at all in these review, interest will focus on the carbon-rich carboranes and the effect of ring size and substituents, both on boron and carbon, in determining the point of equilibrium between the cyclic organoborane and the isomeric carborane cluster. A typical significant example would be the potential interconversion of the l,4-dibora-2,5-cyclohexadiene system (7) and the 2,3,4,5-tetracarbahexaborane(6) system (8) as a function of substituents R (Eq. 2). 

These workers found that the efficiency of oxidation was a function of the residence time of the sample in the reactor and the flow rate of the carrier gas. A high precision of carbon dioxide determination was achieved at a sample flow rate of 50 ml/h and a carrier gas flow rate of 621/h, of which 401/h passes through the shielded zone. 

For tungsten and molybdenum carbides, an increase in substrate surface temperature leads to an increase of the lattice parameter of the film as a result of the increase in carbon concentration. The concentration seems to reach a maximum close to 50 mol% for 500 K in the Mo-C system and 700 K in the W-C system. At these temperatures, the respective M2C phase appears (Table 14.2). Figure 14.2 shows a plot of the carbon concentration (determined by AES) as a function of the substrate temperature. An opposite behaviour was observed for the nitrogen concentration in Mo-N films. Figure 14.3 shows that the N concentration in the a-MoN, phase (fee) decreased with substrate temperature.11 The phase domains were determined by X-ray and electron diffraction. No nitrogen was detected by AES in the Mo bee phase. No significant effect of temperature was observed on W-N films and Cr-N films. 

Figure 14.2 Carbon concentration (determined by AES using the sensitivity coefficients of table 1) in fi-WC, and 6-MoC,. films as a function of the temperature of the substrate the total gas pressure was 1.33 Pa and the applied voltage was 3000 V.

Bronsted exponents for base catalysed proton transfer from carbon acids determined by an acidity function technique in mixed solvents... 

A number of other proton transfer reactions from carbon which have been studied using this approach are shown in Table 8. The results should be treated with reserve as it has not yet been established fully that the derived Bronsted exponents correspond exactly with those determined in the conventional way. One problem concerns the assumption that the activity coefficient ratios cancel, but doubts have also been raised by one of the originators of the method that, unless solvent effects on the transition state are intermediate between those on the reactants and products, anomalous Bronsted exponents will be obtained [172(c)]. The Bronsted exponents determined for menthone and the other ketones in Table 8 are roughly those expected by comparison with the values obtained for ketones using the conventional procedure (Table 2). For nitroethane the two values j3 = 0.72 and 0.65 which are shown in Table 8 result from the use of different H functions determined with amine and carbon acid indicators, respectively. Both values are roughly similar to the values (0.50 [103], 0.65 [104]), obtained by varying the base catalyst in aqueous solution. The result for 2-methyl-3-phenylpropionitrile fits in well with the exponents determined for malononitriles by general base catalysis but differs from the value j3 0.71 shown for l,4-dicyano-2-butene in Table 8. This latter result is also different from the values j3 = 0.94 and 0.98 determined for l,4-dicyano-2-butene in aqueous solution with phenolate ions and amines, respectively. However, the different results for l,4-dicyano-2-butene are to be expected, since hydroxide ion is the base catalyst used in the acidity function procedure and this does not fit the Bronsted plot observed for phenolate ions and amines. The primary kinetic isotope effects [114] also show that there are differences between the hydroxide ion catalysed reaction (feH/feD = 3.5) and the reaction catalysed by phenolate ions (kH /kP = 1.4). The result for chloroform, (3 = 0.98 shown in Table 8, fits in satisfactorily with the most recent results for amine catalysed detritiation [171(a)] from which a value 3 = 1.15 0.07 was obtained. 

Figure 2. Examples of the behavior of the error function defined by equation [4] in determining local model free parameters. Shown are contours of the error function determined by sampling reasonable ranges of values for and xe. Examples are shown for the methyl carbons of Ile-3 and the alpha carbons of Ile-44 and Leu-69. Reproduced with permission from Wand et al. (1996). Copyright 1996 American Chemical Society.

The iodine number of activated carbon was determined in the beginning of the experiment, as well as at particular stages of column functioning, just before changing the column operating mode. 

As in the case of catalysts for oxygen reduction, the surface properties of Pt catalysts for methanol oxidation are governed by both the preparation method and the nature of carbon support. As discussed above, the presence of surface groups such as carboxylic, carbonyl, phenolic, lactone, and pyrone functionalities determine... 

When you perform calculations, such as using half-life of carbon to determine the age of the skull in Figure 22 or the pH of the products in Figure 23, you may need to use the log or antilog function on your calculator. A logarithm (log) is the power or exponent to which a number, called a base, must be raised in order to obtain a given positive number. This textbook uses common logarithms based on a base of 10. Therefore, the common log of any number is the power to which ten is raised to equal that number. Examine Table 4. Note the log of each number is the power of ten for the exponent of that number. For example, the common log of 100 is two and the common log of 0.01 is -2. 

C3H2O3 CH=CHOCO II 0 Vinylene carbonate MW Planar based on variation of rotational constants. No potential function determined. Isotopic species studied 135, 136)... 

Based on comparison of data from UV, fluorescence, and NMR spectroscopy, and from carbon isotope determination for humic substances isolated from coastal and open ocean environments, the authors have concluded the following (1) other than its metal complexation and redox functions, the only resemblance between humic substances from open ocean (marine) and terrestrial environments is that they are both colored organic acids soluble in water, and (2) marine humic substances are formed in situ and only in the coastal zone is there an admixture of terrestrially derived humic substances from rivers. However, this second conclusion has not yet been reconciled with the observations discussed by Mayer in Chapter 8 that riverine humic... 

It is thus clear that there is a network of relations between the functions determining the folllowing partitions octanol - water (Pow), water - biota (BCF), water - generic organic carbon in sediment (Koc), water - atmosphere (Hc) — and between each of them and thermodynamic properties such as aqueous solubility (S), vapor pressure (P), and melting point (Tm). 

Substance 0 was obtained from the flowers of C. autumnale by chromatographic separation of the mother liquors from the crystallization of colchicine (303). The material, m.p. 254 256°, [a]o —144° (chloroform), contains four methoxyl groups and one acetyl function. A carbon-hydrogen determination was not reported, but on the basis of the methoxyl and acetyl determination, a molecular formula, CgjHjjNOe, was proposed. The tropolone ring appears to be absent. 

Electrostatic interactions between the carbon surface and the active-phase precursors have also to be taken into account in the preparation of carbon-supported catalysts. The presence of oxygen functionalities on the carbon surface, which can be produced upon the activation process (for activated carbons) and/or by subsequent oxidation treatments, renders it amphoteric. This implies that it can be more or less charged, positively or negatively, depending on the pH of the surrounding solution. Preparation variables such as the polarity of the solvent, the pH of the solution, the anionic or cationic nature of the metal precursor, and the isoelectric point (lEP) of the carbon support determine the extent of precursor-support interaction and, in this way, the total uptake and dispersion of the active phase in the final catalyst [17,20,37]. Thus, for carbons containing acidic surface groups and, as a consequence, a low isoelectric point, best results in the preparation of supported catalysts are achieved when a cationic precursor is used in basic media. Under these conditions, the acidic complexes (-COOH, -OH) are deprotonated (-COO , -0 ) in such a way that... 

Figure 6.9 NO conversion at 473 K as a function of the nitrogen content of the carbon catalyst determined by XPS. (Data from ref. 129.)...

Limited information exists in the literature, however, on the homo- or copolymerization of vinyl ethylene carbonate, 1 (VEC or 4-ethenyl-l,3-dioxolane-2-one) for the preparation of cyclic carbonate functional polymers. A few comments regarding polymerization of VEC are given in an early patent [9], In the only reported study of the copolymerization behavior of VEC, Asahara, Seno, and Imai described the copolymerization of VEC with vinyl acetate, styrene, and maleic anhydride and determined reactivity ratios [10. Their results indicated that VEC would copolymerize well with vinyl acetate, but in copolymerizations with styrene, little VEC could be incorporated into the copolymer. VEC appeared to copolymerize with maleic anhydride, however the compositions of the copolymers was not reported. Our goal was to further explore the use of VEC in the synthesis of cyclic carbonate functional polymers. 

Solution Copolymerizations. Our primary objective in this preliminary study was to gain a qualitative understanding of the copolymerization behavior of VEC with various types of unsaturated monomers. Particularly, we wanted to determine if VEC could be incorporated into a variety of polymer types of interest to the coatings industry. Since VEC is used to provide cyclic carbonate functionality for subsequent reaction or crosslinking, limited amounts of VEC are used in the copolymerizations. A semi-batch process was used in the copolymerization experiments to approach starved-feed conditions. Starved-feed conditions can result in copolymers with more uniform composition since the conversion is kept high in the reactor. While there are a large number of variables to consider, we elected to focus on monomer composition, polymerization temperature, and initiator level. 

Determination of Carbon Functional Group Concentrations The concentration of aromatic and aliphatic carbons may be obtained using some simple assumptions. The stoichiometry of the aliphatic portion of the sample can be estimated and C(ar) can be calculated using a method suggested by Brown and Ladner (14). The method determines C(ar) by difference. 

Pittman CU, Jiang W, He GR, Gardner SD, Oxygen plasma and isobutylene plasma treatments of carbon fibre Determination of surface functionality and effects on composite properties, Carbon, 36(1-2), 25-37, 1998. 

TITRIMETRIC METHODS FOR CARBON FIBER SURFACE FUNCTIONALITY DETERMINATION... 

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