Assignment of the absolute configuration of (+)-5,5′,6,6′-tetrahydro-7,7′-spiro[7H-cyclopenta[b]pyridine], a new inherently chiral spiropyridine, by a nonempirical analysis of its circular dichroism spectrum

Claps, Michele; Parrinello, Nunziatina Laura; Saá, Carlos; Varela, Jesús A.; Caccamese, Salvatore; Rosini, Carlo

doi:10.1016/j.tetasy.2006.04.034

Cited by 5 publications

(3 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The CE sign of weak 1 L b band was not correctly predicted with the latter two functionals. The long-range separated functionals such as LC-B3LYP and CAM-BLYP may be potential alternatives to better describe the electronic transitions for certain difficult cases, but further assessment of such methods on the present system was beyond the scope of this study. Although there are many examples of successful reproduction and interpretation of the CD spectra of chiral molecules by the cost-efficient yet reliable TD-DFT method, the coupled cluster methods are certainly preferred (where possible) for such molecules that possess well-behaved ground states as well as excited states reasonably well described by single excitation.…”

Section: Resultsmentioning

confidence: 99%

Theoretical and Experimental Studies on Circular Dichroism of Carbo[n]helicenes

2012

View full text Add to dashboard Cite

The chiroptical properties of a series of carbo[n]helicenes (n = 4-10) were investigated by the state-of-the-art approximate coupled cluster and density functional theory calculations. The theoretical calculation at the RI-CC2/TZVPP//DFT-D2-B97-D/TZVP level nicely reproduced the experimental CD spectra in both excitation energy and rotational strength without any shift or scaling. These calculations afforded the electric and the magnetic transition dipole moment vectors in [n]helicenes, allowing us to discuss the observed rotational strengths as a function of the number of benzene rings. Although the observed CD intensity was not immediately correlated to any of the calculated parameters, the anisotropy (g) factor of the (1)B(b) band and the specific rotation were found inversely proportional to n and nicely correlated with the helical pitch, but discontinuous at n = 6, where the aromatic rings start to overlap. In contrast, the g factor at the (1)B(a) band was rather insensitive to n. It was also revealed that the excitation energies of the (1)B(b) and (1)B(a) bands are inversely proportional to n over the entire range of n examined. The theoretical predictions also enabled us to rectify the erroneous experimental CD spectra of [5]- and [6]helicenes reported earlier, by using the enantiopure samples resolved by chiral HPLC.

show abstract

Section: Resultsmentioning

confidence: 99%

Theoretical and Experimental Studies on Circular Dichroism of Carbo[n]helicenes

2012

View full text Add to dashboard Cite

show abstract

“…Such a large amount of exact exchange in BH-LYP and B2-PLYP methods seems to diminish the problems related to the self-interaction error, and thus outperform in reproducing the UV and CD spectra of anti - dAD . The long-range separated functionals such as LC-B3LYP and CAM-BLYP may be a potential alternative to better describe the electronic transitions for certain difficult cases, but further assessment of such methods on the present system was beyond the scope of our study. Although we will eventually employ the results of the more accurate RI-CC2/TZVPP calculations in the following discussion, the BH-LYP and B2-PLYP methods may be of reasonable choice when the system in mind is relatively large and the expensive methods such as the RI-CC2 calculation become practically not feasible.…”

Section: Resultsmentioning

confidence: 99%

Theoretical and Experimental Investigations of Circular Dichroism and Absolute Configuration Determination of Chiral Anthracene Photodimers

et al. 2012

View full text Add to dashboard Cite

Substituted anthracenes photodimerize to stereoisomeric [4 + 4] cyclodimers, some of which are inherently chiral. Recent supramolecular photochirogenic studies enabled the efficient preparation of specific stereoisomers, the absolute configurations of which should reflect the chiral environment of supramolecular host or scaffold employed but have not been determined, hindering detailed mechanistic elucidation and further host/scaffold design. In this study, we performed the combined experimental and state-of-the-art theoretical analyses of the circular dichroism spectra of chiral cyclodimers of 2-anthracenecarboxylic and 2,6-anthracenedicarboxylic acids to reveal the configurational and molecular orbital origin of the Cotton effects observed, and unambiguously determined the absolute configurations of these chiral cyclodimers. The present results allow us to directly correlate the enantiotopic face-selectivity upon photocyclodimerization with the absolute configuration of the cyclodimer derived therefrom and also to precisely elucidate the chiral arrangement of two cyclodimerizing anthracenes.

show abstract

“…46 In particular, transitions at 300 nm (3 ¼ 1800 M À1 cm À1 ), 237 nm (3 ¼ 12200 M À1 cm À1 ) and 221 nm (3 ¼ 33200 M À1 cm À1 ), are of p / p* type and prominent; the last one has its transition electric dipole moment along the long axis of the molecule. The UV-Vis spectrum of pyridine as a chromophore, [47][48][49][50] however, is similar to that of benzene and characterized with a broad band at $270 nm consisting of two almost degenerate electronic transitions: a symmetry allowed, but weak, p / p* transition at 260 nm (3 ¼ 2000 M À1 cm À1 ) and a weaker n/ p* transition at longer wavelengths $270 nm; the corresponding electric transition moments are in plane for the p / p* state and perpendicular to the same plane for the n / p* state. The UV-Vis spectrum of compound (R)-2 (Fig.…”

Section: Uv-vis and CD Spectroscopic Studies Of Model Compounds (R/ S)-2mentioning

confidence: 99%