Amide group nonplanar

Attempts to achieve macrocycles that are capable of stabilizing highly oxidized transition metal complexes has led to the design of noninnocent ligands. The structures of high-valent chromium (V) oxo species with the two tetraamido N ligands (36) and (37) were determined. Both structures were found to contain distinctly nonplanar amide groups, and in (36) all four amides are nonplanar. 

Marks and co-workers [10] studied the relation between inducing activity and structure in this class of compounds. The important generalization was derived that the compounds which are most active in this class are nonplanar and have sterically hindered esters or amide groups. Possibly steric hindrance may protect these compounds from hydrolytic enzymes which would convert them to more water-soluble and thus perhaps less inducing compounds. 

Out-of-plane deformations of the amide group from the stable planar form involve the pyramidalization of the amine group and/or twisting around the CO-N bond, which may be accompanied by pyramidalization of the carbonyl carbon atom. The stmcture and properties of nonplanar amides and lactams have been recently reviewed. ... 

Lactams are generally more reactive toward nucleophiles than are normal amides. The ease of the nucleophilic attack on the lactam carbonyl group is usually attributed to either relief of strain upon opening the ring [68], or to a reduction in the usual amide resonance due to nonplanarity of the bicyclic system [69]. However, the evidence to support unusual strain in the ring or reduced amide resonance in /3-lactam antibiotics is ambiguous. 

Structure determined by three dimensional Taken as imido group H bond parallel tc There is evidence for nonplanar amide ... 

Eor most common amides, cleavage is quite difficult, but in the case of an aziridine which has significantly reduced participation in amide resonance because of the nonplanar amide moiety, " hydrolysis is much simpler as shown in the illustration below. As the lone pair and the carbonyl group become more orthogonal (thereby reducing the level of resonance), the rate of amide hydrolysis increases. Aziridines are also less basic facilitating hydrolysis. 

Figure 4. Four different conformations observed for peptide backbones in cyclic tetra-peptides. The amide bonds in the two conformations containing all-trans peptide groups are nonplanar.

The most active compounds for induction have the following properties They are relatively water-insoluble, lipid-soluble molecules. They are most often nonplanar. If they contain esters or amides, these groups are sterically hindered [10]. 

These effects are a consequence of the collapse of what, in suspension, are highly nonplanar lamellae (27-29). The nonplanarity can take several forms but arises because molecular inclination to lamellar normals increases the surface area per end group or fold and so reduces surface congestion, as is common for the alkane subcell. The simplest polyethylene geometries are hollow p5T amids that form, at higher temperatures, with 312 fold surfaces in 110 sectors and a common c-axis (30). The adoption of 31f planes is thought to reflect the assrmmetric shape of sharp folds, both within and normal to the fold plane. 

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