6-Methoxy-3,3’,3’-Trimethylspiro[2H-1-Benzopyran-2,1’[2]Oxaindan]: Separation Of Enantiomers, Circular Dichroism Measurements And Determination Of The Absolute Configuration (original) (raw)
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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
Journal of Chemical Crystallography, 2010
The title compounds C 11 H 16 Cl 2 O 3 (III) and C 11 H 16 Br 2 O 3 (IV) have been prepared from (S)-Limonen. Their crystal structure and absolute configuration have been determined by X-ray analysis which confirmed the 1 0 S absolute configuration at the cyclopropyl moiety, in agreement with the known absolute configuration of the starting material. Both (III) and (IV) are orthorhombic, space group P2 1 2 1 2 1 with a = 7.2558(4) Å (for III) 7.4058(6) Å (for IV), b = 9.7885(5) Å (for III) 9.7459(7) Å (for IV), c = 17.7551(10) Å (for III) 18.0354(14) Å (for IV), a = 90°, b = 90°, c = 90°and Z = 4.
Tetrahedron, 2013
We dedicate this work to the memory of Carlo Rosini, who suggested undertaking this study before his premature death Keywords: ORD ECD VCD Vibronic features Absolute configuration Conformations Phenyl hindered rotation a b s t r a c t Three forms of chiroptical spectroscopies, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and optical rotatory dispersion (ORD) have been employed to study the configuration and conformational properties of the three molecules: (S)-3-phenylcyclopentanone, (S)-3phenylcyclohexanone, and (S)-3-phenylcycloheptanone (including (S)-3-phenylcyclopentanone-2,2,5,5d 4 and (S)-3-phenylcyclohexanone-2,2,6,6-d 4 ). ECD and VCD spectra in the mid-IR for the three molecular systems are marginally dependent on fine conformational details, as interpreted in terms of standard DFT computational methods, with common spectroscopic features to the three systems clearly identified. Accounting for vibronic coupling mechanisms reproduces the structuring of ECD n/p* band. The ORD curves are quite similar for the three types of molecules, but their interpretation highlights a crucial role played by conformations of the cycloalkanone ring in the case of (S)-3phenylcycloheptanone. The same conclusions are reached by considering the VCD spectra in the CHstretching region.
The Journal of Physical Chemistry A, 2006
Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (89-99% enantiomeric excess (ee)), and their vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra have been recorded. The experimental spectra are compared to theoretical spectra obtained from quantum mechanical calculations (density functional theory with the B3LYP hybrid exchange correlation functional with 6-31++ G**, aug-cc-pVDZ, or aug-cc-pVTZ basis set) and ...
Chemical Research in Toxicology, 2009
The assignment of absolute configurations is of critical importance for understanding the biochemical processing of DNA lesions. The diastereomeric spiroiminodihydantoin (Sp) lesions are oxidation products of guanine and 8-oxo-7,8-dihydroguanine (8-oxoG), and the absolute configurations of the two diastereomers, Sp1 and Sp2, have been evaluated by experimental and computational optical rotatory dispersion (ORD) methods. In order to support our previous assignments by the ORD method, we calculate the electronic circular dichroism spectra (ECD) of the Sp stereoisomers. Comparison of the experimentally measured and computed ECD spectra indicates that Sp1 has (−)-S absolute configuration, while Sp2 has (+)-R absolute configuration. Thus, the S and R assignments, based on the ECD spectra of Sp1 and Sp2, are consistent with our previous assignments of absolute configurations. To further test the validity of this approach, we performed a proof-of-principle computation of the ECD and ORD of the R and S enantiomers of allantoin (similar in chemical composition to Sp) of known absolute configurations. The calculations provide the correct assignment of the absolute configurations of the allantoin enantiomers, indicating that the computational TDDFT approach is robust for identifying the absolute configurations of allantoins, and probably the Sp stereoisomers, as has been shown previously for other organic molecules.
Journal of the American Chemical Society, 2005
The infrared (IR) and vibrational circular dichroism (VCD) spectra of S-2,2′-dimethyl-biphenyl-6,6′-dicarboxylic acid, S-1, in CDCl3 solution are concentration-dependent, showing that oligomerization occurs with increasing concentration. DFT calculations support the conclusion that the oligomer formed is the cyclic tetramer (S-1)4, in which S-1 monomers are linked by hydrogen(H)-bonded (COOH)2 moieties. Due to the existence of two inequivalent tautomeric conformations of each (COOH)2 moiety, six inequivalent conformations of (S-1)4 are possible. B3LYP/6-31G* DFT calculations predict that the conformation "aaab", possessing three equivalent (COOH)2 conformations, a, and one tautomeric conformation, b, has the lowest free energy. B3LYP/6-31G* IR and VCD spectra vary substantially with conformation. The B3LYP/6-31G* IR and VCD spectra of the CdO stretch modes of "aaab" are in excellent agreement with the experimental spectra, while those of all other conformations exhibit poor agreement, confirming the prediction that the "aaab" conformation is the predominant conformation. Comparison of the calculated IR and VCD spectra of the six conformations to the experimental spectra in the range 1100-1600 cm-1 further supports this conclusion. The study is the first to use VCD spectroscopy to determine the structure of a supramolecular species.
The three possible dimethylsubstituted phenyloxiranes (cis, trans and geminal) were synthesized in both racemic (mCPBA) and enantiomerically enriched forms (Shi epoxidation) and subjected to a vibrational circular dichroism study. The experimental spectra were compared to theoretical spectra obtained using DFT/B3LYP calculations, and the differences between experiment and theory are discussed. The absolute configuration at the benzylic position was established as being (R), (S) and (R) for the cis, trans and geminal dimethylsubstituted phenyloxiranes, respectively. In all three cases the configuration of the major enantiomer was in accordance with a simple transition state model based on the spiro reaction mode.
Non-Linear Optical Properties Study of Two Heterocyclic Compounds
International Journal of pharma and Bio Sciences
In an attempt towards understanding the relation between molecular structure-nonlinear optic activity (NLO) among heterocycles, with special reference to the identity, number and position of the heteroatom, semiempirical calculations were carried out. This paper reports the Non-linear optical properties of two heterocyclic compounds namely 3-[2-Oxo-2-(2-oxo-2H-chromen-3-yl)ethylidene]-1,3-dihydro-indol-2-one (3OCEDI) and Quinolin-8-ol (QL). To understand the Non-Linear Optical properties of coumarin dyes we computed dipole moment (μ), electronic polarizability (α), and the mean was first hyperpolarizability (βo) using B3LYP density functional theory method in conjunction with 6-31G(d, p) basis set.All the calculations were carried out in gas phase and in acetonitrile medium. The optimized geometry of both compounds shows a 3D helical structure. The results indicate that given the same number and type of atoms and double bonds in a molecule, linear conjugation excels over cyclic or crossed conjugation in enhancing hyperpolarizabilities and it seems to be far more critical than a chiral centre.