Carbonyl linkage

C=N—, linkage and water. The reaction of carbonyl compounds with secondary and tertiary amines generally does not result in the formation of an azomethine linkage. Carbonyl compounds having an a-hydrogen atom react with secondary amines to give enamines. When, however, the perchlorate salts of the secondary amines are employed, ternary iminium salts are obtained . The reaction of certain cyclic ketones with tertiary amines at low temperatures results in unstable complex formation. ... 

The coordination and organometallic chemistry of zirconium and hafnium are surveyed for the year 1991.107,108 There is useful material in a review of homogeneous Group 4 metallocene Ziegler-Natta catalysts, a review of the coordination chemistry of cyclopentadienyl titanium carboxylate and related complexes O and a review of bis(cycIopentadienyl)zirconium(IV) or hafnium(IV) complexes with Si-, Ge-, Sn-, N-, P-, As-, Sb-, 0-, S-, Se-, Te- or transition metal-centred anionic ligands. Cationic zirconocene or hafiiocene complexes serve as Lewis acids with unique reactivities, they are active for C-F bond activation, coordinative activation of ether linkages, carbonyl activation and C-O bond cleavage. New synthetic methods based on the... 

This oxidation proceeds readily if the methylene group is activated by linkage to (a) a carbonyl group, (b) an aromatic ring (c) an olefine link also activates adjacent CH2 and CH groups. 

Analysis We can disconnect both the symmetrical a,p-imsaturated carbonyl linkages ... 

Fig. 7. Reactions of ttiglycetides at the carbonyl ester linkage. R represents the alkyl side chain.

The aromatic core or framework of many aromatic compounds is relatively resistant to alkylperoxy radicals and inert under the usual autoxidation conditions (2). Consequentiy, even somewhat exotic aromatic acids are resistant to further oxidation this makes it possible to consider alkylaromatic LPO as a selective means of producing fine chemicals (206). Such products may include multifimctional aromatic acids, acids with fused rings, acids with rings linked by carbon—carbon bonds, or through ether, carbonyl, or other linkages (279—287). The products may even be phenoUc if the phenoUc hydroxyl is first esterified (288,289). 

The carbonyl groups in the diketo- and keto-aleohol bases are not readily detected by the usual reagents and as these bases can be reduced to the dihydrie alcohols, it was assumed at first that lobeline and lobelanine contained one and two ether linkages respectively and formulse based on this assumption, and satisfying the other experimental evidence then available, were put forward by Wieland, Schopf and Hermsen, of which that for lobeline (II) may be quoted as an example. 

The peptide linkage is usually portrayed by a single bond between the carbonyl carbon and the amide nitrogen (Figure 5.3a). Therefore, in principle, rotation may occur about any covalent bond in the polypeptide backbone because all three kinds of bonds (N——C, and the —N peptide bond) are sin-... 

FIGURE 5.2 The peptide bond is shown in its usnal trans conformation of carbonyl O and amide H. The atoms are the oi-carbons of two adjacent amino acids joined in peptide linkage. The dimensions and angles are the average valnes observed by crystallographic analysis of amino acids and small peptides. The peptide bond is the light gray bond between C and N. (Adapted from Ramachandran, G. A., ct ai, 1974. Biochimica Biophysica Acta 359 298-302.)... 

The ant Iridomyrmex pruinosus utilizes 2-heptanone as an alarm pheromone. Figure 17 illustrates the existence of a close correlation of the similarity between 2-heptanone and its analogs in molecular model silhouettes with their alarm activity45. It is noteworthy that the replacement of the methylene group in position 3 of 2-heptanone by the ether linkage yields n-butyl acetate which has the same activity as the natural pheromone. Considerable activity is still retained even when the carbonyl group is replaced by the hydroxyl group. 

Naturally occurring compounds called cyanogenic glycosides, such as lotau-stralin, release hydrogen cyanide, HCN, when treated with aqueous acid. The reaction occurs by hydrolysis of the acetal linkage to form a cyanohydrin, which then expels HCN and gives a carbonyl compound-fa) Show the mechanism of the acetal hydrolysis and the structure of the cyanohydrin that results. 

Monosaccharides normally exist as cyclic hemiacetals rather than as open-chain aldehydes or ketones. The hemiacetal linkage results from reaction of the carbonyl group with an —OH group three or four carbon atoms away. A... 

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