Non-equivalence, and Configuration

Inversion, Non-equivalence, and Configuration.— Lowering of the inversion barrier of the acylphosphine (49) by conjugation of the phosphorus lone pair of electrons with the carbonyl group was confirmed by the sensitivity of inversion to the nature of Non-equivalence of the apical fluorine atoms in 

Inversion, Non-equivalence, and Configuration.—Analysis of SCF-LCAO calculations indicates that whereas the inversion of ammonia is dominated by electronic repulsions, the inversion of phosphine is controlled by nuclear repulsion. The phosphorus f/-orbital functions markedly affected the properties of both the pyramidal and planar states.  

study of the inversion of phosphole derivatives such as (55) has shown that even in complex spin systems a relatively accurate estimate of the inversion barrier may be obtained without recourse to a complete lineshape analysis. In this study, alkyl and aryl substituents did not 

Non-equivalence of the methylene protons of (62) was observed for a solution in carbon tetrachloride but not for a solution in deuterium oxide - a solvent which could break up the intramolecular hydrogenbonding shown in (62). Also, non-equivalence of the methyl groups was 

The diastereomeric salt of (—)-a-phenylethylamine with the (—)-thioic acid (64) has a Sp at lower field than that with the (+)-thioic acid.  

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Table 7.2 Terms arising from some configurations of non-equivalent and equivalent electrons...

Much literature precedent supports the assignment of tacticity in methyl acrylate polymers using NMR techniques [40,41]. In the H-NMR spectrum, the shift of the methylene protons is sensitive to dyad stereochemistry. For example, in an isotactic (meso) dyad 28, the methylene protons are chemically non-equivalent and appear as two separate sets of signals, whereas in a syndiotactic (racemic) dyad 29, the methylene protons are equivalent. The H-NMR spectrum of 27 showed multiplets at 1.89 and 1.5 ppm due to the two diastereotopic methylene protons of the isotactic dyad. The rest of the spectrum is consistent with the structure of the n=4 tetrad 27. A racemic dyad structure would have been expeeted to give resonances of intermediate shift to that of the two resonances observed for the telomer 27. This evidence strongly implies that 27 has the allisotactic configuration shown in Scheme 8-12. 

Distinct NMR resonances were first observed for the enantiomers of 2,2,2-trifluoro-l-phenylethanol in the presence of (/ )-phenylethylamine. With (/ )-2-naphthylethylamine the magnitude of the non-equivalence was increased. A systematic study of a series of aryl alcohols in the presence of amines showed a consistent correlation between the sense of non-equivalence and the absolute configuration of the alcohol. From the simple solvation models proposed, the reciprocality of the CSA approach is evident, i.e. if chiral A can be used to assay racemic B then chiral B can be used to assay racemic A. With this in mind 1 -(9-anthryl)-2,2,2-trifluoroethanol (15a) was developed as a CSA for chiral amines. It is also effective with alcohols, lactones, a-amino acid esters, a-hydroxy acid esters and sulphoxides and is the most widely used chiral solvating agent. Other more specific solvating agents have been developed. Kagan has developed A -(3,5-dinitrobenzoyl)-l-phenylethylamine,forexample, as a CSA specifically for the assay of chiral sulphoxides prepared from sulphides by a modified Sharpless oxidation (section 6.3.2). 

For a 7C% 1 configuration in which two non-equivalent n orbitals (i.e., orbitals whieh are of n symmetry but whieh are not both members of the same degenerate set an example would be the n and 7i orbitals in the B2 moleeule) are oeeupied, the above analysis must be expanded by ineluding determinants of the form 7iia7i ia, ... 

If is inferesfing fo nofe fhaf of fhe 5, S, P, P, and farms which arise from two non-equivalent p electrons, as in the s 2s 2p 3p configuration of fhe carbon atom, only 5,... 

In the excited electron configuration given, there are two electrons in partly filled orbitals, a Ad (electron 1) and a 5/ electron (electron 2). These are non-equivalent electrons (Section 7.1.2.3a) and we need consider only the coupling of the orbital angular momenta, fj andf2> and the spin angular momenta, Sj and S2-... 

It has 6-coordination with a chelating acetate [106] and may be converted (reversibly) into Ru(OAc)2(PPh3)3, which has the/ac-configuration with one monodentate and one bidentate acetate. It is fluxional at room temperature but at —70°C the phosphines are non-equivalent on the NMR timescale [107],... 

Reaction of 1-nitropropane with glutaraldehyde in aqueous ethanol in the presence of sodium hydroxide yields a mixture of two products, the major component of which, lr-ethyl-l-nitrocyclohexane-2c,6f-diol (98), can be isolated in 36% yield ). Acid-catalyzed acetylation converts (98) into the di-O-acetate, hydrogenation yields the corresponding amine, which has been characterized as the hydroacetate, N-acetate and triacetate. Configurational assignments followed from NMR data, which clearly showed the steric non-equivalence of the two hydroxyl groups vicinal to the tertiary center. 

The relative configuration of adjacent, constitutionally non-equivalent, carbon atoms can be specified as erythro or threo, as appropriate, by adding the required prefix to the terms diisotactic and disyndiotactic , as necessary (see Section 2.2). 

Again, if the two electrons are non-equivalent, all possible couplings arise (e.g., a % % 1 configuration yields 3A, 3E, 3E, JA, JE, and JE states). In contrast, if the two electrons are equivalent, certain of the term symbols are Pauli forbidden. Again, techniques for dealing with such cases are treated later in this Chapter. 

A set of pairs of quantum numbers n,7, with the indicated number of electrons having these quantum numbers, is called an electronic configuration of the atom (ion). Thus, we have already discussed the cases of two non-equivalent electrons and a shell of equivalent electrons. If there is more than one electron with the same nf, then the configuration may look like this ... 

In order to indicate the parity, defined here as (—l),1+ 2, we have to add to the term a special symbol (e.g. for odd configurations the small letter o). Then, for example, the levels of the configuration nsn p will be lP[, 3 0,1,2- Thus, the spectra of two non-equivalent electrons will consist of singlets and triplets. 

Let us notice that momenta of each shell may be coupled into total momenta by various coupling schemes. Therefore, here, as in the case of two non-equivalent electrons, coupling schemes (11.2)—(11.5) are possible, only instead of one-electronic momenta there will be the total momenta of separate shells. To indicate this we shall use the notation LS, LK, JK and JJ. Some peculiarities of their usage were discussed in Chapters 11 and 12 and will be additionally considered in Chapter 30. Therefore, here we shall restrict ourselves to the case of LS coupling for non-relativistic and JJ (or jj) coupling for relativistic wave functions. We shall not indicate explicitly the parity of the configuration, consisting of several shells, because it is simply equal to the sum of parities of all shells. 

Part 2 is devoted to the foundations of the mathematical apparatus of the angular momentum and graphical methods, which, as it has turned out, are very efficient in the theory of complex atoms. Part 3 considers the non-relativistic and relativistic cases of complex electronic configurations (one and several open shells of equivalent electrons, coefficients of fractional parentage and optimization of coupling schemes). Part 4 deals with the second-quantization in a coupled tensorial form, quasispin and isospin techniques in atomic spectroscopy, leading to new very efficient versions of the Racah algebra. 

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