Carboxyl Chemical composition

Structural keys describe the chemical composition and structural motifs of molecules represented as a Boolean array. If a certain structural feature is present in a molecule or a substructure, a particular bit is set to 1 (true), otherwise to 0 (false). A bit in this array may encode a particular functional group (such as a carboxylic acid or an amidelinkage), a structural element (e.g., a substituted cyclohexane), or at least n occurrences of a particular element (e.g., a carbon atom). Alternatively, the structural key can be defined as an array of integers where the elements of this array contain the frequency of a specific feature in the molecule. 

Goal Constitution. Chemical composition studies (35,36) indicate that brown coals have a relatively high oxygen content. About two-thirds of the oxygen is bonded carboxyl, acetylatable hydroxyl, and methoxy groups. Additionally, unlike in bituminous coals, some alcohoHc hydroxyl groups are beheved to exist. 

Hemozoin, also known as malaria pigment, is, in teims of its chemical composition, identical to (3-hematin. Hemozoin is formed as a crystallization product of heme under the acidic conditions present in the food vacuole of malarial parasites. In the crystal, the heme molecules are linked into dimers through reciprocal iron-carboxylate bonds to one of the propionate side chains of each porphyrin. The dimers form chains linked by hydrogen bonds. 

The chemical composition of B. papyrifera olibanum is markedly different from that of other Boswellia, with small amounts of monoterpenes and sesquiterpenes, large amounts of w-octanol (18) and -octy I acetate (40), with the latter being the major compound, and the presence of particular diterpenes [incensole (127), incen-sole acetate (129), incensole oxide (130) and incensole oxide acetate (131)] and the absence of both isoincensole and isoincensole acetate (128). Linear carboxylic acids from hexanoic acid (10) to lauric acid (93) were also identified in B. papyrifera olibanum exclusively. 

In contrast to the other large cats, the urine of the cheetah, A. jubatus, is practically odorless to the human nose. An analysis of the organic material from cheetah urine showed that diglycerides, triglycerides, and free sterols are possibly present in the urine and that it contains some of the C2-C8 fatty acids [95], while aldehydes and ketones that are prominent in tiger and leopard urine [96] are absent from cheetah urine. A recent study [97] of the chemical composition of the urine of cheetah in their natural habitat and in captivity has shown that volatile hydrocarbons, aldehydes, saturated and unsaturated cyclic and acyclic ketones, carboxylic acids and short-chain ethers are compound classes represented in minute quantities by more than one member in the urine of this animal. Traces of 2-acetylfuran, acetaldehyde diethyl acetal, ethyl acetate, dimethyl sulfone, formanilide, and larger quantities of urea and elemental sulfur were also present in the urine of this animal. Sulfur was found in all the urine samples collected from male cheetah in captivity in South Africa and from wild cheetah in Namibia. Only one organosulfur compound, dimethyl disulfide, is present in the urine at such a low concentration that it is not detectable by humans [97]. 

In spite of this variation in molecular weights and solubilities humic acid and fulvic acid have a very similar chemical composition. These acids consist of aromatic moieties such as phenols, benzenepolycarboxylic acids, hydroxybenzenepolycarbo-xylic acids, 1,2-dihydroxybenzene carboxylic acids, together with more complex condensed structures and polycylic compounds. It is conjectured that these various units are joined together by aliphatic chains (45, 54) the distribution of functional groups is presented in Table 5. 

Nakagami, T. and Yokota, T. (1978a). Esterification of wood with unsaturated carboxylic acids IV Chemical composition and molecular weight of the acetone-soluble fraction of (I-methylcroto-nylated woods. Mokuzai Gakkaishi, 24(5), 311-317. 

To date, the composition of active sites is known for many enzymes, the most probable action mechanisms are suggested, and comparison data exist on catalytic group properties in enzymes and free molecules in solutions. Note also that the chemical composition of catalytic active sites of enzymes is independent of the presence of any specific compounds. Moreover, the majority of them are the well-known compounds for homogeneous catalysis histidine imidazole, carboxylic groups of aspartic and aminoglutaric acids, flavins, hemins, etc. However, as homogeneous catalysts, they possess rather moderate or even poor catalytic activity in appropriate reactions. 

Kobayashi et al. studied catalyst systems in which the chemical composition of the Nd-carboxylates was varied in terms of their electron-withdrawing properties Nd(OCOR)3 (R = CF3, CC13> CHC12, CH2C1, CH3) [177]. In this study the highest activity was found for Nd(OCOCCl3)3-based systems. 

We have performed two kinds of analyses in order to determine the chemical composition of the liquid products. First, we analyzed die elemental con osition of the product. The raw material is composed of 76,2% of C, 9.6% of H and 14.2% of O (percentages in mass). Sulfur was also analyzed, but it was not detected (detection limit = 0.05%). These percentages siqipose an H-to-C ratio of 1.52. For the hydrogenated products, no oxygen was detected, except for experiment EXP04 (1.25% in mass). Therefore, we can affirm that carboxylic groups are either completely reduced to -CHj or removed as CO. ... 

Problem 18.22 The residue left upon ignition of a sodium salt of a carboxylic acid was white, soluble in water, turned moist litmus blue, and reacted with dilute hydrochloric acid with the formation of bubbles. What was its probable chemical composition ... 

Choice of solvent. The solvent cannot be selected on the basis of rules or theoretical considerations but must be experimentally determined. There are certain theoretical considerations which serve as a general guide for example, it is known that naphthalene, CioHs, is insoluble in water, H2O, but soluble in benzene, CeHe. From similar studies the general rule is drawn that a solid is best dissolved in a liquid which it resembles in chemical composition and structure. An organic carboxylic acid RCOOH is expected to dissolve in water since it contains the hydroxyl group, OH but if... 

The structural formula reveals that this polymer contains two different types of carboxyl group which have different dissociation constants. While the first dissociation step is characterized by a pK value of 3.4, the pK value of the second step is about 7.4. Both pK values were determined via titration of the prepolymer with sodium hydroxide solution. The exchange capacity of the finished stationary phase is directly proportional to its polymer content. It may be calculated in advance, since, owing to the chemical composition, the concentration of the exchange groups in the prepolymer is known. 

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