Quadrant rules

Fig. 31.7 Modern presentations of the Quadrant Rule for predicting the course of enamide hydrogenation, following the original work of Knowles.

Fig. 31.12 (a) X-ray structure of the enamide complex that corresponds to the correct" hand of product (from [58]). Solvent hydrogens and counterion are omitted for clarity, (b) Structure of the cation in (a), (c) Application of the Quadrant Rule by these authors. 

The possibility of application of the quadrant rule for the IV-chloramine derivatives was discussed, and a similar rule was also proposed for the /V-cyano derivatives96. 

X-ray and CD analysis. The structure of procyanidin B-1 was unequivocally confirmed by x-ray analysis of its deca-(9-acetyl derivative by Weinges, one of the pioneers in the field of proanthocyanidin chemistry. One of the most powerful methods to establish the absolute configuration at C-4 of the T-unit in dimeric A- and B-type proanthocyanidins remains the chiroptical method via application of the aromatic quadrant rule. This has been repeatedly demonstrated by the author s own work and several other contributions listed in Refs. 7-12. 

DeAngelis, G.G. and Wildman, W.C., Circular dichroism studies. 1. A quadrant rule for the optically active aromatic chromophore in rigid polycyclic systems. Tetrahedron, 25, 5099, 1969. 

While for several phanes such as [njparacyclophanes, dioxa[n]para or [2.2]meta-paracyclophanes, the assignments by this rule were in agreement with the experimental results, they had to be revised for [2.2]meta- and [m][n]paracyclophanes after the application of more reliable methods. These discrepancies were discussed in previous sections (2.6.1, 2.9.1). A quadrant rule proposed for cyclic ketones includes also the configurational assignment to oxo[2.2]metacyclophanes (61-63) and stereoisomeric alcohols derived therefrom 113). 

Subsequently, the application of a quadrant rule developed for compounds bearing an asymmetric center adjacent to the aromatic chromophore by means of considerations of the CD and ORD spectra of products of established absolute configuration to the alkaloids of the 5,10b-ethanophenanthridine series led to conclusions on their absolute stereochemistry at variance with those mentioned above 42). 

Fig. 28 Quadrant rule for R-Z-Z-R chromophores (Z = S, Se, Te). Top Experimental and calculated CD spectra of dichalcogenide diselenide. Calculations were performed at the B3LYP/ TZVP level of theory. Bottom The quadrant rule for the P/M helicity of dichalcogenides. Data to prepare the figure were taken from [287]...

According to the mechanism of the enantioselective reduction, a concept has been evolved, termed the quadrant rule [81, 82]. This model addresses how the chiral ligand influences the preferential addition of hydrogen either to the re- or si-face of a C = X bond. As visualized in Fig. 3.30, upon coordination of the ligands to the metal atom, the substituents are oriented in such a way that... 

Scott and Wrixon have developed a quadrant rule for the c.d. of platinum(ii)-olefin complexes that depends on d-d orbital transitions. Application of the rule to monoterpenes was considered, and generally conformed to expectations based on known absolute configurations, but in some cases (notably 8-pinene) the results were not satisfactory. The complex measured may be that of a-pinene, for which a Cotton curve of the opposite sign is predicted. Further work on the use... 

A full report on the c.d. of square-planar complexes formed between chiral olefins and sodium tetrachloroplatinate shows that a quadrant rule (Figure 6) predicts the sign of the Cotton effect near 440 nm for a range of disubstituted and some trisubstituted ethylenes. The Pt atom is considered to bond to the less-hindered face of the olefinic bond. Despite the success of the quadrant rule... 

The availability of a large number of mono-, di-, tri-, and tetra-substituted allenyl steroids has made possible a study of their chiroptical properties. This led to a bifurcated quadrant rule which relates the configuration of the substituents to the sign of the lowest-energy Cotton effect. 

On the lowest level, using symmetry and nodal properties of the MOs of H2C=0 as a representative of the inherently symmetric carbonyl chromophore, an octant rule can be derived for the influence of a (static) perturber of the (n, n ) excitation The geometrical symmetry (C2v) of the H2C=0 unit with the two symmetry planes, yz and xz, leads to a quadrant rule. If the orbitals involved in the (n, n ) excitation of ketones are described as " = 2p and n = N 2p — 2pJ) (N being a normalization constant), the nodal plane (xy) of the virtual orbital generates the octant diagram for the contributions of substituents of chirally perturbed compounds (Figure 10). 

Partial molar rotatory powers [37]. Due primarily to the work of Litman and Schellman [38], it now appears that a quadrant rule is most appropriate for a peptide chromophore, in which case the sign does not change with the -(-z and — z directions. As for distance dependence, there are two dominant terms, r and r , which are of opposite sign with the term relevant to the above discussion and dominating at distances greater than 3 A. A statement of has been written for the methyl moiety perturbing a peptide n-n transition [38]... 

Charge-transfer complexes of dissymmetric olefins with either tetracyano-ethylene or Pt (sodium tetrachloroplatinate) exhibit chiroptical effects related to the chirality of the olefin. TT)e Pt complexes generally obey a Quadrant Rule. Chiral olefins may also be converted into osmate esters, exhibiting Cotton effects in the region of 480 nm the sign obeys a chirality rule (Figure 3) which... 

Unlike the Cu(II) complexes of other L-amino acids, that of L-histidine yields a positive d-d Cotton effect. Also, on the basis of the CD spectra of L-proline, L-hydroxyproline, and L-phenylglycine amide complexes of Cu(II) and Ni(II), which show positive Cotton effects in the d-d transition region, the adequacy of the hexadecant rule has been questioned (Wellman et ai, 1969) together with the planar rule (C2h), quadrant rule (C2v), and octant rule (/>2h) The several sector rules have been compared and discussed by Martin (1974, pp. 129-156). 

A quadrant rule (Fig. 3) for the n-71 Cotton effect of the N-dithiocar-bomethoxy (dithiourethane) chromophore R—S—CS—has been proposed (Ripperger and Schreiber, 1965 Ripperger, 1967, 1969). According to the experimental results, the signs are as shown in Fig. 4. It has been stated that this quadrant rule can be applied to pyrrolidines and open-chain compounds. 

Figure 3. Quadrant rule for dithiocarbamates. (From Ripperger, 1969. Reproduced with permission of Pergamon Press, Inc.)...

Figure 16. Quadrant rule for the amide chro-mophore. (From Schellman, 1968. Reproduced with permission of the American Chemical Society.)...

A sector rule for the rotatory strength of low-symmetry chromophores such as lactones, lactams, and peptides (Fig. 17) has been described by Ong et al (1977) and Weigand (1979, and references therein) and compared with the quadrant rule (Schellman, 1968). One of the most important conclusions is that the longest-wavelength singlet absorption (based on the perturbation theory) of an ester group and that of an amide arise from basically different... 

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