The octant rule. 15. Antioctant effects: synthesis and circular dichroism of 2-exo- and 2-endo-alkylbicyclo[2.2.1]heptan-7-ones and bicyclo[3.2.1]octan-8-ones

Chiroptical properties and molecular geometry of substituted succinic anhydrides and imides

“…spectra of these compounds, the higher energy n-n* band is shifted to the red and strongly overlaps with the second n-n* band which is slightly shifted to the blue. Both bands are still discernible in the imide (11) but only a single band at 240 nm of double intensity is observed for compound (12) (Figure 5). The change of the n-n* transition energy in (11) and (12) probably results from the electronic interactions of electron lone pairs on substituent oxygens with the chromophore orbitals in these high symmetry molecules.…”

“…An increased dielectric constant of the solvent diminishes these interactions giving an enhanced population of the equatorial form in polar media; compare the spectra of (8b) in water and hexafluoropropan-2-01 (HFP). Even stronger dipole-dipole interactions, stabilizing the diequatorial form, are expected for tartrimide (11) and its 0,O'-di-t-butyl derivative (12). This was evidenced by the C.e.…”

Asymmetric meta-arene–alkene photocycloaddition controlled by a 2,4-pentanediol tether

“…7 Acid treatment of 3a and 3b resulted in the cleavage at the cyclopropyl group, regioselectively, 8 with subsequent hydrogenation over a Pd-C catalyst giving 5 in 40% yield (Scheme 4). The structure of the intermediate was determined by the spin-decoupling experiments.…”

Chromatographic enantiomer separation and absolute configuration of spiro[benzo-1,3-dioxole-2,9′-bicyclo[3.3.1]nonan]-2′-one and the corresponding diastereomeric hydroxy acetals

“…These results conform with the observation that β-axial hydroxy groups do not make "antioctant" contributions, unlike alkyl groups, and this also confirms that the shape and location of the third nodal surface differ from substituent to substituent. 8 Thus an analysis of the CD spectra of hydroxyacetals 3a,b has permitted us to assign the absolute configuration of the compounds presented in Scheme 2.…”

“…7 The failure of the octant rule for 1 could be explained by the interaction of the two carbonyl chromophores since they are placed close to the nodal planes where the Cotton effects change sign. 8 A further insight into understanding the rules relating the signs of the Cotton effect to the absolute configurations could be obtained by a study of chiral bicyclononanes of a suitable molecular structure. Molecules containing the carbonyl and other chromophores in a comparatively well defined spatial relationship are very interesting from this point of view.…”