Optical activity. I. Rotational strengths of twisted ethylene, nonplanar 1,3-butadiene, and the chiral methylcyclohexanones from molecular orbital wave functions (original) (raw)
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Chirality, 2002
We report ab initio calculations of the frequency-dependent electric dipole-magnetic dipole polarizabilities, b(m), at the sodium D line frequency and, thence, of the specific rotations, [a] D , of 2,7,8-trioxabicyclo[3.2.1]octane, 1, and its 1-methyl derivative, 2, using the Density Functional Theory (DFT) and Hartree-Fock/Self-Consistent Field (HF/SCF) methodologies. Gauge-invariant (including) atomic orbitals (GIAOs) are used to ensure origin-independent [a] D values. Using large basis sets which include diffuse functions DFT [a] D values are in good agreement with experimental values (175.8°and 139.2°for (1S,5R)-1 and -2, respectively); errors are in the range 25À35°. HF/SCF [a] D values, in contrast, are much less accurate; errors are in the range 75À95°. The use of small basis sets which do not include diffuse functions substantially lowers the accuracy of predicted [a] D values, as does the use of the static limit approximation: b(m) » b(o)
Theor Chem Acc, 2008
The Absolute configuration (AC) of the chiral alkane D 3 -anti-trans-anti-trans-anti-trans-perhydrotriphenylene (PHTP), 1, is determined by comparison of density functional theory (DFT) calculations of its vibrational circular dichroism (VCD) and optical rotation (OR) to the experimental VCD and OR of (+)−1, obtained in high enantiomeric excess using chiral gas chromatography. Conformational analysis of 1 demonstrates that the all-chair (CCCC) conformation is the lowest in energy and that other conformations are too high in energy to be significantly populated at room temperature. The B3PW91/TZ2P calculated IR spectrum of the CCCC conformation of 1 is in excellent agreement with the experimental IR spectrum, confirming the conformational analysis and demonstrating the excellent accuracy of the B3PW91 functional and the TZ2P basis set. The B3PW91/TZ2P calculated VCD spectrum of the CCCC conformation of S-1 is in excellent agreement with the experimental VCD spectrum of (+)−1, unambiguously defining the AC of 1 to be S(+)/R(−). The B3LYP/aug-cc-pVDZ calculated OR of S-1 over the range 589-365 nm has the same sign and dispersion as the experimental OR of (+)−1, further supporting the AC S(+)/R(−). Our results confirm the AC proposed earlier by Farina and Audisio. This study provides a further demonstration of the excellent accuracy of VCD spectra predicted using Stephens' equation for vibrational rotational strengths together with the ab initio DFT methodology, and further documents the utility of VCD spectroscopy in determining the ACs of chiral molecules.
International Journal of Quantum Chemistry, 2015
A theoretical procedure has been developed and implemented to calculate the optical rotation of chiral molecules in ordered phase via origin-independent diagonal components j 0 xx ð2x; xÞ; j 0 yy ð2x; xÞ, j 0 zz ð2x; xÞ of the optical activity tensor and origin-independent components A a;bc ð2x; xÞ, for a 6 ¼ b 6 ¼ c, of the mixed electric dipole-electric quadrupole polarizability. Origin independence was achieved by referring these tensors to the principal axis system of the electric dipole dynamic polarizability a ab ð2x; xÞ at the same laser frequency x. The approach has been applied, allowing for alternative quantum mechanical methods based on different gauges, to estimate near Hartree-Fock values for three chiral molecules, (2R)-N-methyloxaziridine C 2 NOH 5 , (2R)-2-methyloxirane (also referred to as propylene oxide) C 3 OH 6 , and (R a )-1,3-dimethylallene C 5 H 8 , at two frequencies. The theoretical predictions can be useful for an attempt at measuring correspondent experimental values in crystal phase.
Prediction of optical rotation using density functional theory: 6,8-dioxabicyclo[3.2.1]octanes
Tetrahedron: Asymmetry, 2000
We report calculations of the optical rotations of six 6,8-dioxabicyclo[3.2.1]octanes using ab initio density functional theory (DFT). GIAO basis sets are used to ensure origin independence of predicted rotations. Large basis sets including diuse functions are used to minimize basis set error. The signs of [a] D are correctly predicted. Magnitudes dier from experiment by 10±20 degrees [dm (g/cc)]^1 on average. Agreement with experiment is improved by inclusion of solvent eects via the Polarized Continuum Model (PCM). The results support the conclusion that DFT/GIAO/PCM calculations of speci®c rotations can be useful in elucidating the absolute con®gurations of chiral molecules. #
Optical Rotation Calculations for Fluorinated Alcohols, Amines, Amides and Esters
The journal of physical chemistry. A, 2016
We have calculated the optical rotation at λ = 589 nm for 45 fluorinated alcohols, amines, amides and esters using both time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional and the second-order approximate coupled-cluster singles and doubles (CC2) method, in both methods adopting the aug-cc-pVDZ basis set. Comparison of CAM-B3LYP and CC2 results to experiments illustrate that both methods are able to reproduce the experimental optical rotation results for both sign and magnitude. Several conformers for molecules containing the benzyloxy and naphthalene groups needed to be considered to obtain consistent signs with experiments and these conformers are discussed in detail. We have also used a two-point inverse power extrapolation of the basis set to investigate the optical rotation in the basis set limit at the CC2 level, however, we only found small differences compared to the aug-cc-pVTZ results. Our results demonstrate that the least computationally expens...
Molecular optical rotation: an evaluation of semiempirical models
Chemical Physics Letters, 2000
Ab initio optical rotations have been obtained for allene, 1,3-dichloroallene, H O , and H S as a function of dihedral 2 2 2 2 Ž . angles, both at SCF and post-SCF levels. The results have been used to test a the concept that the molecular optical rotation can be written as a Ý M sin u , where u is the dihedral angle of the ith X-A-A-X type segment and M is a
Chirality, 2010
Density Functional Theory (DFT) calculations of optical rotation (OR) and vibrational circular dichroism (VCD) have been used to assign the absolute configuration (AC) of a recently prepared (3-phenyloxirane-2,2-diyl)bis(phenylmethanone), 3, by asymmetric epoxidation of the corresponding 2-arylidene-1,3-diketone. The experimental OR at 589.3 nm and the VCD spectrum of the (1)-and (2)-enantiomer of 3 have been measured. The conformationally-averaged OR value and VCD spectrum of (R)-3 were calculated at B3LYP/6-311G(2d,2p) level of theory. Both approaches provide the same absolute configuration of the stereogenic carbon, i.e. the AC of (1)-3 is (R)-3, thus affording a confident assignment. Only two conformational isomers of 3 have been predicted to be populated at ambient temperature. Their presence is directly observed in the VCD spectrum. Chirality 22:E130-E135, 2010. V
Circular dichroism of some high-symmetry chiral molecules: B3LYP and SAOP calculations
Theoretical Chemistry Accounts, 2009
Computational modeling of optical activity, circular dichroism (CD) and optical rotatory dispersion, is rapidly becoming a useful supplement to experimental studies of absolute configuration. Here, we investigate the predictions of two alternative formulations of the rotational strength based on time-dependent density functional theory (TD-DFT), for a series of high symmetry chiral systems. We employ the TD-DFT method as realized in Gaussian 03 suite with the hybrid functional B3LYP and as incorporated in the Amsterdam density functional (ADF) suite with PBE and SAOP functionals. The high-symmetry systems described here are somewhat larger than those used to evaluate the influence of basis sets and density functional choice, and for such large systems the very extensive basis sets recommended by most investigators may not be suitable for routine use. We observe that useful results for these systems can be obtained in modest bases, and in particular that diffuse functions may not be required for informative use of the ADF implementation. The statistical average of orbital potentials (SAOP) model developed by Baerends is essential to the success of the ADF implementation. In some cases chirality is defined by features of the molecular structure remote from the chromophore. This is a severe test of the TD-DFT theory, since high-lying excitations define the most prominent features of the CD spectra, and complicates the use of computations to guide the assignment of absolute configuration. Experimental investigation of the high symmetry systems described here is desirable.
The Journal of chemical …, 2002
We report an implementation for the computation of optical rotations within the Amsterdam Density Functional program package. The code is based on time-dependent density functional response theory. Optical rotations have been calculated for a test set of 36 organic molecules with various density functionals, and employing basis sets of different quality. The results obtained in this work with nonhybrid functionals are comparable in quality to those recently reported by other authors for the B3LYP hybrid functional, but show a somewhat larger tendency to produce outlyers. The median error is approximately 20°/(dm g/cm 3) for specific rotations ͓␣͔ D as compared to experimental data ͑approximately 30% median deviation from experimental values͒. Thereby it is demonstrated that density functional computations can be employed to assist with the solution of stereochemical problems in case the specific rotations of the species involved are not small and their structures are rigid. Recent newly developed functionals are investigated with respect to their applicability in computations of optical rotations.