Carbon atoms, chemical synthesis

Since pantothenic acid contains an asymmetric carbon atom, chemical synthesis yields the racemic mixture. On the other hand, when enzymatic synthesis is used, only the biologically active form of pantothenic acid is produced. 

In the 1890s, Nef mentioned that the functional group —NC of the isocyanides contains a divalent carbon atom C° and therefore there is a large difference between their chemistry and that of the other chemical compounds that contain only tetravalent carbon atoms Any synthesis of isocyanides corresponds to a conversion of into and all chemical reactions of isocyanides correspond to transitions of the carbon atoms C into... 

The fungus responsible for Dutch elm disease is spread by European bark beetles when they burrow into the tree Other beetles congregate at the site attracted by the scent of a mixture of chemicals some emitted by other beetles and some coming from the tree One of the compounds given off by female bark beetles is 4 methyl 3 heptanol Suggest an efficient synthesis of this pheromone from alcohols of five carbon atoms or fewer... 

Write a balanced chemical equation for (a) the reaction between sodium hydride and water (b) the formation of synthesis gas (c) the hydrogenation of ethene, H,C= GH2, and give the oxidation number of the carbon atoms in the reactant and product (d) the reaction of magnesium with hydrochloric acid. 

First, the short chain length PHAs, poly(HASCL), are composed of monomeric units containing up to 5 carbon atoms. The most well-known representatives are poly(3-hydroxybutyrate) (PHB), and its copolymers with hydroxyvalerate. Of all the PHAs, PHB is by far the most commonly encountered in nature [18]. It is the simplest PHA with respect to chemical structure, having a methylene (-CH3) group as the pendent R-unit in Fig. 1. Owing to its enzymatic synthesis, PHB has an exceptional stereochemical regularity. The chains are linear and the chiral centers all are in the R-stereochemical conformation, which implies that this polymer is completely isotactic. 

The starting materials for the chemical synthesis of kojic acid are also carbohydrates, but only hexoses and their derivatives have been used for this purpose. Maurer and his coworkers studied the synthesis extensively in order to clarify the mode of formation of the 7-pyrone system from carbohydrates. They succeeded in preparing di-O-acetylkojic acid (XLIII) by purely chemical means, first from D-glucose54 and then from D-galac-tose.67 The mechanism of formation of XLIII, which does not contain any asymmetric carbon atoms, was apparently not dependent on the configura-... 

Porphyrazines (pz), or tetraazaporphyrins, are compounds that can be viewed as porphyrin variants in which the meso carbon atoms are replaced with nitrogen atoms, as Fig. 1 shows (1). This difference intrinsically gives porphyrazines discrete physiochemical properties from the porphyrins. In addition, despite their similar molecular architecture, porphyrazines are prepared by an entirely different synthetic route than porphyrins—by template cyclization of maleonitrile derivatives, as in Fig. 2, where the open circle with the A in it represents the peripheral substituent of the pz—rather than by the condensation of pyrrole and aldehyde derivatives (1). The pz synthetic route allows for the preparation of macrocycles with chemical and physical properties not readily accessible to porphyrins. In particular, procedures have been developed for the synthesis of porphyrazines with S, N, or O heteroatom peripheral functionalization of the macrocycle core (2-11). It is difficult to impossible to attach the equivalent heteroatoms to the periphery of porphyrins (12). In addition, the preparation and purification of porphyrazines that bear two different kinds of substituents is readily achievable through the directed cocyclization of two different dinitriles, Fig. 3 (4, 5, 13). 

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