Inversion, atomic

Atomic Inversion, Pyramidal (Lambert) Axially and Planar Dissymmetric Molecules, Absolute Configuration 6 19... 

Polypeptide Stereochemistry Goodman, Verdini, Choi and Masuda).. Pyramidal Atomic Inversion Lambert). 

The question might be asked Are there similar mechanisms for changing the configuration of molecules without breaking bonds in molecules with coordination numbers other than 3 and 5 The answer is yes. One of the most important series of inorganic compounds consists of six-coordinate chelate compounds exemplified by the tris(ethylenediamine)cobalt(lIl) ion. Because of the presence of the three chelate rings, the ion is chiral and racemization can take place by a mechanism that is closely related to atomic inversion or Berry pseudorotaiion (the mechanism for six-coordination is termed the Bailar twist see Chapter 13k... 

A detailed ab initio and modified neglect of diatomic overlap (MNDO) study of structural parameters and pyramidal phosphorus atom inversion and also enthalpy differences between the participants in the conformational equilibrium (axial and equatorial) of 1-R-phosphorinanes (R = H, CH3, C2H5) has been investigated and is in good agreement with the observed NMR and X-ray values <1999IJB660>. 

Quaternary ammonium salts with asymmetric nitrogen atoms. Inversion of configuration is not possible because there is no lone pair to undergo nitrogen inversion. For example, the methyl ethyl isopropyl anilinium salts can be resolved into enantiomers. 

From these studies, two motional processes have been postulated, a low-energy pseudorotational motion and a higher-energy arsenic atom inversion process. Detailed equilibrium studies have been conducted involving ring, chain, and oligomeric forms of these species. ... 

An N-bonded thiocyanate or isothiocyanate will be termed an N-thiocyanato complex and its formula will be written M—NCS, and an (S-bonded or normal thiocyanate will be termed an jS-thiocyanato complex, written M—SON the corresponding formalism will apply to the other ions. Where the mode of coordination is not known the complex will be termed thiocyanate and written M—CNS. Beck and Fehlhammer (86) have rightly objected to this atom inversion, against chemical knowledge, but it, nevertheless, remains a convenient shorthand and is not likely to cause confusion in this review which contains few, if any, references to fulminates, thiofulminates, etc. 

Configurational stability of Ph(/-Pr)2SiLi has been estimated by means of H NMR [Eq. (9)] (24). The two methyl groups in each isopropyl group are diastereotopic and anisochronous at room temperature in a wide range of solvents. The nonequivalence is observed up to I85°C. Since rotation around the Si-C bonds appears to be fast on the NMR time scale, the nonequivalence of the isopropyl methyl groups in the anion is evidence for slow inversion about silicon. This result indicates that unimolecular atomic inversion about silicon must be slow on the NMR time scale, and a lower limit to inversion about the trivalent silicon can be set at about 24 kcal/mol, which is consistent with theoretical studies (see Section VIII). 

Atomic Inversion The simplest reaction a molecule such as ammonia can undergo is the inversion of the... 

Trisubstituted atoms with a lone pair, such as amines, may undergo the process of pyramidal atomic inversion on the NMR time scale. The resonances of the two methyls in the aziridine 5-15 become equivalent at elevated temperatures through rapid nitrogen inversion. 

The results are shown as Arrhenius plots in Fig. 28.4. In view of the large OKIE, there can be little doubt that QMT dominates the H-atom inversion. Furthermore, the Arrhenius plot for H-atom inversion is curved and the rate con-... 

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