Abstract
The fact that the dissymmetry lgeb (g-factor) of camphor is large has been known for decades, and the interpretation of the observed data has also been known for a long time. However, due to the ability of quantum chemical methods to describe chiroptical phenomena more appropriately, additional approaches based on these methods have been successful employed. The g-factor lgebra in S-camphor and L-tryptophan have been investigated by UV-Vis and electronic circular dichroism (ECD) spectroscopies of the n ® p* electronic transition. Time-dependent density functional theory (TD-DFT) calculations at CAM-B3LYP/6-311++G(3df,2p)//B3LYP/6-311++G(2d,p) level of theory including Grimme’s dispersion effects have been performed. The lgebra effect was added using solvation model based on density (SMD) approach in solvation environment. The results permit insights into the ground and excited states electronic properties associated with the g-factor. The theoretical spectra showed good similarity with the experimental ones. The theoretical ECD of camphor was found at 282 nm, whereas the experimental shows its maximum at 290 nm. Regarding the maximum value of the molar absorptivity lgebrante, the theoretical and experimental values were 16.2 and 30.2 M-1 cm-1, respectively. The same concordance was obtained for g-factor, as follows: -0.0445 and -0.0886, for experimental and theoretical results, respectively.
Highlights
This work has its background in the ab initio calculation of the UV-Vis absorption and electronic circular dichroism (ECD) spectra for camphor as have been commonly used, such as optical rotatory dispersion (ORD) and ECD spectroscopy.[1,2,3,4,5]ECD is a chiroptical spectroscopic technique based on differential absorption by a chiral molecule of left (Al) and right (Ar) circularly polarized light in the UV and visible regions
Of ECD or absorbance properties, the g-factor is independent of concentration and path length, i.e., it is an intensive property of a chiral compound
In this work we have studied the electronic and molecular properties of the S-enantiomer (Figure 1a) and, for comparative purpose, of the L-tryptophan (Figure 1b)
Summary
This work has its background in the ab initio calculation of the UV-Vis absorption and electronic circular dichroism (ECD) spectra for camphor as have been commonly used, such as optical rotatory dispersion (ORD) and ECD spectroscopy.[1,2,3,4,5]ECD is a chiroptical spectroscopic technique based on differential absorption by a chiral molecule of left (Al) and right (Ar) circularly polarized light in the UV and visible regions (equation 1). In case where there are several conformers which appear to be stable in terms of energy, as L-tryptophan (Figure 1b), ECD calculations generally involve two steps: first the conformational analysis of the compound to obtain the most relevant conformational structures, weighted considering the Boltzmann distribution law (equation 3).
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