Amides, structure

Although these reactions suggest the possibility of a tautomeric equilibrium between the amide and imidol forms in the A -unsub-stituted compounds, the ultraviolet,fluorescence, and infrared spectra of a series of such compounds support the amide structure only. 

Although three possible structures (11a, 12, and 13) of kasugamycin were considered on the basis of the stoichiometrical data presented previously, the amide structure (11a) was excluded as already described. 

UV spectra of a variety of 1 -alkyl-1 //-1-benzazepines,20,21 3//-l-benzazepines,20 l-acyl-l//-l-benzazepines,1 3,22,23 3-acyl-3//-3-benzazepines,22-23 3-alkyl-37/-3-benzazepines and their cations in concentrated sulfuric acid,24,25 and 3-mesyl-3//-3-bcnzazepine,2ft have been recorded. A comparison of the UV spectra of 3-alkyl-l, 5-dihydroxy-3//-3-benzazepinc-2,4-dicarboxylates and their bis-O-methyl ethers supports an enol rather than an amide structure for these derivatives.14... 

Prigge, S. T., Mains, R. E., Eipper, B. A. and Amzel, L. M. New insights into copper monooxygenases and peptide amidation structure, mechanism and function. Cell Mol. Life Sci. 57 1236-1259, 2000. 

Biodegradable polyesters are also made by copolymerization of aliphatic and aromatic forms, or by polyester amide structures. The molecular structures need... 

Stabilized with respect to the amide structure, is some 30 kcal mole less stable than the O-protonated form, therefore refers to gas phase protonation. Molecular orbital calculations by Hopkinson and Csizmadia (1973) put the same difference at only 6-2 kcal mole , again ignoring solvation. 

Chart 3. Cyclization of citrate siderophores to amidic structures... 

Hydroxy- and 4-hydroxy-pyridines are in equilibrium with their tautomeric amide structures containing a carbonyl. These tautomers are called 2-pyridone and 4-pyridone respectively. This type of tautomerism does not occur with the corresponding benzene derivative phenol, since it would destroy the stabilization conferred by aromaticity. 

There have been several reviews on alkali metal amide structural chemistry. Most of these deal with lithium amides but there is also significant coverage of the heavier elements and other topics such as derivatives of primary amides and hydrazides. " Two comprehensive reviews for lithium amides and related salts published in 1991 and 1995 include extensive tables of structural data. There have also been reviews of the of lithium amides as well as of the extensive use of alkah metal... 

In order to get information on the surface species responsible for the spectra obtained after adsorption of both cyclic nitro compounds, the adsorption of several potential intermediates has been investigated. It can be concluded from the adsorption of isocyanic acid that the absorption around 2190 cm 1 can be due to surface isocyanate species. To explain the absorption bands in the range 1600-1200 cm1, the first idea was a surface amide structure, such as was observed by Krietenbrink et al.,IS However, considering the low stability of this adsorption complex and the disappearance of the band around 1475 cm1 when going from C6HSN02 to C6D5N02 (a shift down to approximately 1395 cm1), the conclusion is arrived at that such an assignment would be incorrect. 

In the first step, the tertiary amide structure is reduced to hemiaminal 31 with the aid of the at complex (30) from D1BAH and butyl-lithium The hemiaminal opens selectively to aminoaldehyde 32 In a second step the ring nitrogen atom is protected as carbamate 11 with ethyl ehloroformate. 

The free energy of activation for the breakdown (AGcleav does not vary con siderably with the amide structure, while that for the conformational change at the nitrogen (aG onf) changes appreciably from the formamide to the acetamide (or propionamide). This confirms that the conformational step is influenced appreciably by the steric interaction of the R group in these N,N-dimethylamides. 

The pungency of the fruits of black pepper (Piper nigrum Piperaceae), a widely used condiment, is mainly due to the piperidine alkaloid piperine (Figure 6.24). In this structure, the piperidine ring forms part of a tertiary amide structure, and is incorporated via piperidine itself, the reduction product of A1 -pipcridcine (Figure 6.22). 

A number of studies have detected Maillard reaction products (melanoidins) in refractory organic matter from natural environments—for example, from sediments from a west African upwelling (Zegouagh et al., 1999) and archeological plant remains (Evershed et al., 1997). Poirer et al. (2000,2002) and Quenea et al. (2006a) showed that the refractory organic matter isolated from different soils consists in part of cross-linked melanoidins poorly resolved by 13C NMR spectroscopy. The presence of amide structures in soil as elucidated by 15N NMR is ascribed to either preserved proteinacious structures or melanoidin-type macromolecules (Derenne and Largeau, 2001). 

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