Carbon derivatives, structural

Kramer, R. W., Kujawinski, E. B., and Hatcher, P. G. (2004). Identification of black carbon derived structures in a volcanic ash soil humic acid by Fourier transform ion cyclotron resonance mass spectrometry. Environ. Sci. Technol. 38, 3387-3395. 

The title of this three-part volume derives from a key theme of the book—the logic underlying the rational analysis of complex synthetic problems. Although the book deals almost exclusively with molecules of biological origin, which are ideal for developing the fundamental ideas of multistep synthetic design because of their architectural complexity and variety, the approach taken is fully applicable to other types of carbon-based structures. 

In view of the activity of 13, but the lack of activity for the alpha-ethyl homolog of DOM, the two isomeric ring-methylated derivatives Structures 16a and 16b were recently prepared (114). Neither isomer showed significant activity, either as an agonist in the rat fundus preparation or in a mouse assay, when compared with 13. It would appear that little bulk can be tolerated near the alpha-carbon, other than a methyl or methylene. 

More novel results were published in the area of the isomeric [l,2,4]triazolo[l,5-c]pyrimidine ring system. In Table 16, a few applications of earlier known methodologies are shown. All these compounds were synthesized by transformation of 4-imino-3-aminopyrimidine or analogous derivatives by reagents providing a one-carbon-atom structural unit (e.g., carboxylic acids or derivatives). 

Oleochemical alcohols are primary, even carbon-numbered structures with a high linearity (>95%), while the petrochemical derivatives can be even or odd numbered, and depending on the process, their linearity can be as high as the oleochemicals (Ziegler alcohols) or can exhibit variable branching (30% modified 0X0-60% standard OXO). 

Dash RK, Yushin G, Gogotsi Y et al (2005) Synthesis, structure and porosity analysis of microporous and mesoporous carbon derived from zirconium carbide. Micropor Mesopor Mater 86(l-3) 50-57... 

In the tryptophan branch (Fig. 22-17), chorismate is converted to anthranilate in a reaction in which glutamine donates the nitrogen that will become part of the indole ring. Anthranilate then condenses with PRPP. The indole ring of tryptophan is derived from the ring carbons and amino group of anthranilate plus two carbons derived from PRPP. The final reaction in the sequence is catalyzed by tryptophan synthase. This enzyme has an a2/32 subunit structure and can be dissociated into two a subunits and a /32 subunit that catalyze different parts of the overall reaction ... 

The structural basis of one of the classic examples of such stereospecificity, that of chymotrypsin for L-amino acid derivatives, is immediately obvious on examination of the crystal structure of the enzyme. D-Amino acid derivatives differ from those of L-amino acids by having the H atom and the side chain attached to the chiral carbon interchanged (structure 8.10). The d derivatives cannot bind because of steric hindrance between the side chain and the walls of enzyme around the position normally occupied by the H atom of L derivatives (Chapter 1). 

It is also possible to derive structural parameters from infrared spectroscopic data and these are (1) saturated hydrogen to saturated carbon ratio (2) paraffinic character (3) naphthenic character (4) methyl group content and (5) paraffin chain length. 

The monocyclic terpene hydrocarbons, many of which are formed readily from the acyclic terpenes by ring closure or from the bicyclic terpenes by ring fission, contain a six-carbon ring and may all be considered as derivatives of either cyclohexane or benzene. They may also be classified, on the basis of common larger fundamental structures, into two distinct types of substituted six-carbon ring structures ... 

When reacting either ethylene carbonate or propylene carbonate with an aliphatic diamine, a polyurethane can be produced (Figure 2.14). Polyethylene ether carbonate) diols (Harris et al., 1990), when fabricated into polyurethanes using MDI and BDO, produce elastomers that have polyester polyol features. This was shown using 13C NMR. The structure gives rise to potential for a very high virtual cross-linking density. These carbonate-derived polyesters have superior hydrolysis resistance compared to the traditional materials. 

Compared with the parent system and those with identical substitution in all four carbons, the structure of other derivatives should be affected by the substitution pattern and by the nature of the substituents. For 1,2-disubstituted derivatives, structure type C, in which the doubly substituted cyclobutane bond is weakened (and lengthened), or a related structure type in which the bond is cleaved, should be favored. This is born out by several observations mentioned earlier. For example, the geometric isomerization of 1,2-diaryloxycyclobutane (Sect. 4.1) can be rationalized by one-bond rotation in a type C radical ion. Similarly, the fragmentation of the anti-head-to-head dimer of dimethylindene (Sect. 4.4) may involve consecutive cleavage of two cyclobutane bonds in a type C radical ion. The (dialkylbenzene) substituents have a lower ionization potential (IP 9.25 eV) [349] than the cyclobutane moiety (IP 10.7 eV) [350] hence, the primary ionization is expected to occur from one of the aryl groups. 

Fig. 8 Overlap of the three pharmacophores representing the interactions found for paclitaxel in the 1JFF structure (A), epothilone A in the NMR-derived structure (B), and epothilone A in the QSAR model from Botta and co-workers (C), respectively. Blue C7-OH (epothilones) oxetane ring (paclitaxel) red C13 carbon (epothilones) phenyl ring (paclitaxel) yellow Cl carbonyl oxygen (epothilones) Cl carbonyl oxygen (paclitaxel) purple thiazole ring (epothilone) C3 benzamide (paclitaxel). (3-tubulin monomer is represented as a green cartoon and residues involved in hydrogen bonds are in orange (hydrogens are omitted for sake of clarity)...

These valency statements are consistent with the characteristic multiplet structures in 4f photoemission and N4 5 x-ray absorption, as well as the low-lying distribution of the occupied carbon-derived MO s. 

As regards the interactions between the encaged metal ions and the host cage, the Sc2 C84 system presents a very different picture to the Ce2 C72 case. In Sc2 C84 the fine structure and branching ratio in the Sc-L2 3 x-ray absorption spectra require a strong hybridisation between the 3d levels of the Sc ions and carbon-derived MO s of the C84 molecules. 

Nitrophenyl chloroformate activation. The reaction of polysaccharides with chloroformates forming reactive carbonate derivatives has often been used to link bioactive compounds, such as affinity ligands and enzymes, onto polysaccharide matrixes. It was reported that upon reaction with ethyl chloroformate cyclic carbonate as well as ethyl-carbonate structures are formed (9-13). Activation with N-succinimi-do chloroformate (14), 2,4,5-trichloroformate (14) and 4-nitrophenyl chloroformate (14, 15) reportedly led to the introduction of pending carbonate moieties. 

The CGMT model was intended to describe (non-cyclic) homonuclear and heteronuclear double-bonded systems. However, in the meantime other multiple-bonded species have also been synthesized, as will be seen in the following. They also often exhibit structural features which are not familiar from the analogous carbon derivatives, and are not yet fully understood. Some of them are, however, related to the phenomena discussed above and may be understood on a similar base. I will not go into details in these cases, but will refer to recent literature when available. 

The Patemo-Buchi reaction on furan has been studied from a theoretical point of view [42]. The HOMO of furan has an energy of 0.32 eV, and the atomic coefficients of this orbital (Fig. 3.3) are in agreement with an attack of the carbonyl oxygen on the a carbon. The structures of the possible adducts deriving from the attack of benzaldehyde in the a position of furan are depicted in Figure 3.4. The exo isomer is more stable (0.5 kcal mol 1) than the other isomer, in agreement with the experimental results. 

Processing of CDC was recently reviewed by Nikitin and Gogotsi [28], Carbon derived from selective etching of metals by halogens has shown great promise as the active material in electrochemical capacitors [15,29-31] because of the structure and properties that can be fine-tuned [21,32] and control of surface functional groups [33],... 

Behavior of Carbethoxynitrene toward Polyisoprene Structures. After studying the reaction of a number of divalent carbon derivatives with polyenes (17, 18), attention was directed to monovalent nitrogen derivatives. Of these, carbethoxynitrene, N—C02Et, gives addition reactions with olefins (12, 13). It can be produced either by photolysis of ethyl azidoformate (12), or by a-elimination (13) (Figure 5). 

The stereochemical factors influencing the formation of cyclic carbonates have not been fully elucidated, and the number of derivatives whose structures have been unequivocally proved is quite small. In fact, the structures of the known cyclic carbonate derivatives of pyranosides have all been allocated on the basis of analogies with corresponding 0-isopropylidene acetals. This is particularly unfortunate where the possibility of both five-and six-membered carbonate rings exists, as in the case of 1,2 3,4- and 1,2 4,6-dicarbonate esters of D-galactopyranose (VII VIII). A five-mem-... 

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