Orbitals amides

Angle subtended by the axes of the nitrogen lone pair and the carbonyl carbon 2p orbital. Amide distortion parameters defined in accordance with Winkler-Dunitz . 

In the allyl anion, carboxylate, and nitro systems we had four electrons in the Tt system spread out over three atoms. The nitrogen in the amide group also has a pair of electrons that could conjugate with the K bond of the car-bonyl P P- Again. f°r effective overlap with the tc bond,, he lowest orbital amide... 

In contrast with amines, amides (RCONH ) are nonbasic. Amides don t undergo substantial protonation by aqueous acids, and they are poor nucleophiles. The main reason for this difference in basicity between amines and amides is that an amide is stabilized by delocalization of the nitrogen lone-pair electrons through orbital overlap with the carbonyl group. In resonance terms, amides are more stable and less reactive than amines because they are hybrids of two resonance forms. This amide resonance stabilization is lost when the nitrogen atom is protonated, so protonation is disfavored. Electrostatic potential maps show clearly the decreased electron density on the amide nitrogen. 

The amide bond that links different amino acids together in peptides is no different from any other amide bond (Section 24.3). Amide nitrogens are non-basic because their unshared electron pair is delocalized by interaction with the carbonyl group. This overlap of the nitrogen p orbital with the p orbitals of the carbonyl group imparts a certain amount of double-bond character to the... 

A further comparison of structures 41 and 42 shows that the main difference between the structures occurs near this same reactive bond. Structure 42 represents the most stable conformation expected of Dalanyl-Dalanine, where the amide is trans substituted and the nitrogen is oriented so that its lone pair of electrons may overlap with the tt orbitals of the carbonyl group. In... 

The value is derived from a zero-field spectrum recorded at 150 K. A q could not be determined at 4.2 K because the compound is in the limit of slow paramagnetic relaxation and the strong unquenched orbital moment forces the internal field into the direction of an easy axis of magnetization. As a consequence, the quadrupole shift observed in the magnetically split spectra results only from the component of the EFG along the internal field and the orientation of the EFG is not readily known dbabh is a bulky N-coordinating amide... 

A priori borataethenes would be expected to be much more stable than the corresponding boraethenes because, as Rundle presciently noted about organometallic structures,50 all low-lying atomic orbitals are involved in the bonding. In fact, the stabilization of 52 is the driving force for the acidity of C—H bonds of proper orientation a to tricoordinate boron. Such acidity was first detected by Rathke and Kow through the treatment of B-methyl-9-borabicyclo[3.3.1] nonane (53) with hindered lithium amides, such as lithium 2,2,6,6-tetramethylpiperidide51 (Eq. 18) ... 

Schafer, L., I. S. Bin Drees, R. F. Frey, C. Van Alsenoy, and J. D. Ewbank. 1995c. Molecular Orbital Constrained Gas Electron Diffraction Study of N-Acetyl N -MEthyl Alanine Amide. J. Mol. Struct. (Theochem) 338, 71-82. 

New examples of the preparation of stannylamines, largely by established methods, are shown in Equations (164) and (165). Sodium bis(trimethylstannyl)amine can be prepared from sodium amide and a stannylamine,499 and can act as the precursor to other bis- and tris(stannyl)amino compounds.499 500 The tristannylamines are planar about the nitrogen, with the unshared pair in a 2p orbital. Tris(chlorodimethylstannyl)amine, with five-coordinate tin, is close to centrosymmetrical, and reacts with pyridine to give a tetrastannabicyclo[3.1.1]heptane.501... 

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