Nitrogen pyramidalization

Section 7 16 Atoms other than carbon can be chirality centers Examples include those based on tetracoordmate silicon and Incoordinate sulfur as the chirality center In principle Incoordinate nitrogen can be a chirality center m compounds of the type N(x y z) where x y and z are different but inversion of the nitrogen pyramid is so fast that racemization occurs vrr tually instantly at room temperature... 

The question of the correctness of such an explanation of the nonplanarity of 2-azirine and the planarity of pyrrole was analyzed in Mo et al. [89JMS(201)17]. The evolution of the MOs as a function of the pyramidalization angle in nitrogen was traced. For both 2-azirine and pyrrole nitrogen pyramidalization leads to the stabilization of all 7t-MOs of the planar structure and, conversely, to the destabilization of several [Pg.368]

The strengthening of the Si N bond is accompanied by a reduction in the XSiO angles and an increase in the nitrogen pyramidalization. These are reflected in the corresponding decrease in the deviation of the silicon atom from the plane of the equatorial oxygen atoms (Asi) and increase in the deviation of the nitrogen atom from the plane of the neighboring... 

The invertomers of the nitrogen pyramid 1-chloro-2,2-dimethylaziridine have been separated by enantioselective complexation GC on the chiral metal chelate nickel(II)-bis[(3-heptafluorobutanoyl)-( l.R>)-camphorate] (Ni-CAM2) in squalane (Schurig et al., 1979). The resolution of the chiral aziridine into two sharp peaks with a = 1.5 in 45 min at 60° C demonstrated the stereochemical integrity of the invertomers (cf. Figure 6). 

Brois, S. J. (1968b) Aziridines. XII. Isolation of a stable nitrogen pyramid. J. Amer. Chem. Soc. 90, 508-509. 

Fig. 5.46 Cyclopropylamine conformations at the B3LYP/6-31G level. Structure 1 is a hilltop whose two imaginary frequencies indicate that it wants to undergo nitrogen pyramidalization and rotation about the C-N bond to form the transition states (nomenclature ts 1/2 connects 1 and 2, etc.) and, eventually, the minima. Each C, species has an enantiomer of the same energy...

Some theoretical works report the geometric features of penams skeleton, considering the strain of the bicyclic system and the bridgehead nitrogen pyramidality (see Section 2.03.3.1). For instance, the two possible conformations (axial and equatorial with respect to the C-3 carboxyl group) of the penicillins thiazolidine ring have been localized as two minima by ab initio calculations employing several theoretical methods (Hartree-Fock (HF), density functional... 

In the case of 6Pfr = bV f = 0 this expression reduces to eq. (3.111). In practice, variation of the one- and two-electron densities on the lone pair (4/ r, bV f < 0) leads to modification of the nitrogen pyramid. Numerical estimates show that the... 

In order to calculate the height Fmax of the potential barrier from the measured tunneling frequencies [see Eq. (6), (7) ref. 3-14>] it is necessary to know the geometry of the molecule (especially the height of the nitrogen pyramid), which may also be obtained from analysis of the microwave spectra. Fitting then a barrier shape function 13> to the observed spectral data leads to the value of Fmax. Thus an approximate shape of the potential curve is obtained. 

FIGURE 3. Enamine nitrogen pyramidality. 0 is L RNR, co is the angle between the extended C—N bond and L RNR bisector. (Reprinted from Ref. 6, p. 16 by courtesy of Marcel Dekker, Inc.). 

Nitrogen pyramidal amides (N-benzoyl-7-azabicyclo[2.2.1]heptanes) 01YZ65. 

Most chiral trisubstituted amines can t be resolved into enantiomers because nitrogen pyramidal inversion occurs loo rapidly, but the substance known as Trdger /i base is an exception. Make a molecular model of Troger s base, and then explain why it is resolvable into enantiomers. 

In hydrazine, NH2NH2, there are only single bonds both nitrogens are like amine nitrogens, pyramidal and sp hybridized. 

Ohwada T (2001) Nitrogen pyramidal amides and related compounds. Yakugaku Zasshi 121 65-77... 

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