N. Berova

Synthesis, absolute configuration and circular dichroism of some diarylmethane derivatives

Abstract Synthesis and assignment of the absolute configuration of different types of compounds bearing the diarylmethane moiety is presented. The absolute configuration was determined using chemical correlation and CD approaches based on the sign of the 0-0 vibronic transition within the α-aromatic ( 1 L b ) band of the substituted phenyl chromophore.

Circular dichroism of optically active 1,2-disubstituted 1,2-diphenylethanes—Part I: The cotton effects within the α-band

Resume Die zwei Phenylchromophore eines optisch aktiven 1,2-disubstituierten 1,2-Diphenylethans geben unabhangig voneinander Cotton-Effekte innerhalb des Wellenlangenbereichs der α-Bande. Durch Bildung der Summen-und Differenz-CD-Kurve fur ein threo/erythro Paar erhalt man CD-Spektren, die fur jedes “Halbmolekul” charakteristisch sind, und die im allgemeinen zwei 0-0—Linien um 37230 cm -1 aufweisen. Aus deren Vorzeichen kann die absolute Konfiguration an jedem der Chiralitatszentren eindeutig bestimmt werden.

Stereochemistry of some diastereoisomeric 2-substituted borneols

Abstract The absolute configurations of the benzylic chiral centers in the four diastereomeric (2-hydroxy-born-2-yl)phenylacetic acids are determined on the basis of the sign of the Cotton effect at about 225 nm of the circular dichroism curves. The favoured conformers are calculated using Allingers 1977 force field. The exo -OH forms are computed to be favoured by about 1 to 1.2 kcal mol −1 with respect to the endo -OH forms.

Conformational energy analysis of substituted diphenylethanes: Part VIII. Conformations of some hydroxy and amino 1-monosubstituted and 1,3-disubstituted 1,2-diphenylpropanes

Abstract Experimental estimates (NMR and IR) of the conformational preferences of some 1-monosubstituted and 1,3-disubstituted 1,2-diphenylpropanes are compared with those calculated by means of Momanys empirical force field (EFF). Except for the erythro 1,3-diol, the NMR J-constants indicate varying degrees of preference for conformations with antiperiplanar hydrogen atoms for both isomers. The EFF calculations agree well for the erythro 1,3-diol, although for the other compounds they tend to exaggerate the strains in the more congested conformations. The orders of preference and the equilibrium shifts, however, correlate satisfactorily with the EFF conformational energies.

Circular dichroism and absolute configuration of chiral phenyl-phenylamino-methanes

Abstract The CD-spectra of 20 phenyl phenylamino methanes and of 2 model compounds are presented. From some of these it was concluded that the absolute configuration assigned before in the literature was incorrect and this has been proved by an X-ray diffraction study of 8 . The absolute configuration of 10 and 11 could be assigned from their very similar CD-spectra. All other compounds had already been chemically correlated with 8 , 10 , or 11 . The CD-spectra are not simply sum-curves of those of the two individual chromophores. Most of them can be explained by the assumption of exciton interaction between their respective p-bands. For 17 to 22 several conformations seem to be possible according to molecular models and no safe CD-correlation can, therefore, be done.