Conformational investigation of two isomeric chiral porphyrins: A convergent approach with different techniques

Abstract

The conformation in solution of two atropisomeric meso-tetrabinaphthyl porphyrins, used as catalytic precursors in asymmetric synthesis, was studied by means of experimental ((1)H-NMR ROESY, UV-Vis, and circular dichroism) and computational (semiempirical structure optimization, DeVoe's coupled oscillators calculations) methods. UV-Vis and CD spectra are calculated for several molecular models, with a systematic sampling of the conformational space, and compared to the experimental ones, leading to a structural hypothesis which is confirmed by NMR and PM3.

Solid‐state Circular Dichroism and Hydrogen Bonding, Part 2: The Case of Hypothemycin Re‐investigated

“…42,48 In these latter, however, very less expensive semi-empirical methods (CNDO or ZINDO) were used for CD calculations. 69,70 CONCLUSIONS Analysis of the results discussed in the present article and comparison with other published data lead to some interesting conclusions. It must be stressed that, at least to a first approximation, exciton-coupled CD may be considered an additive property.…”

Structural determinations by circular dichroism spectra analysis using coupled oscillator methods: An update of the applications of the DeVoe polarizability model

“…Salvadori and co-workers 45 did a study on a more complex system, constituted by the two isomeric chiral porphyrin derivatives 17 and 18 in Chart 11. They were interested to carry out a conformational analysis of these molecules used as catalytic precursors in enantioselective oxidations.…”

Electronic Circular Dichroism

“…For compound 8, this is found for q ¼ 75 and y ¼ 75 , and for compound 9, for q ¼ 90 and y ¼ 90 . Semiempirical geometry optimizations and considerations on the 1 H-NMR chemical shifts further support this assignment [24].…”

“…One of the most complex cases treated so far is represented by porphyrins 8 and 9, which differ in atropisomerism around the two bonds indicated by gray straight arrows depicted in Scheme 9.4 [24]. NMR reveals that the two species are endowed with C 4 and D 2 symmetry, respectively.…”