Circular dichroism at microwave frequencies: Calculated rotational strengths of selected transitions for some oxirane derivatives

1997 ◽  
Vol 107 (7) ◽  
pp. 2175-2179 ◽  
Author(s):  
W. R. Salzman
Keyword(s):  
Circular Dichroism ◽  
Microwave Frequencies ◽  
Circular Dichroïsm ◽  
Rotational Strengths

Electronic and Vibrational Circular Dichroism of Model β-Lactams: 3-Methyl- and 4-Methylazetidin-2-one

1996 ◽  
Vol 50 (5) ◽  
pp. 630-641 ◽  
Author(s):  
Jennifer McCann ◽  
Arvi Rauk ◽  
Gennadii V. Shustov ◽  
Hal Wieser ◽  
Danya Yang
Keyword(s):  
Circular Dichroism ◽  
Ab Initio ◽  
Electronic Transition ◽  
Vibrational Circular Dichroism ◽  
Protic Solvent ◽  
Free Energies ◽  
Chiroptical Properties ◽  
Circular Dichroïsm ◽  
Rotational Strengths ◽  
Simple Modeling

The chiroptical properties of the simplest chiral β-lactams, 3- and 4-methylazetidin-2-one, 1 and 2, respectively, were investigated. The experimental vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra were measured and compared with ab initio predictions. Both compounds were found to form dimers with calculated binding enthalpies and free energies of about −51 kJ/mol and −6 to −8 kJ/mol, respectively. The experimentally measured IR and VCD spectra were measured in concentrated nonpolar (CCl4) solution and are in agreement with the predicted IR and VCD spectra of the dimeric forms, 12 and 22, but not the monomers. The most intense dimer VCD bands originate from in-plane N-H wags, which perturb the H-bonded cyclic array. At the more dilute concentrations employed for the ECD spectra, the experimental ECD spectra in heptane were interpreted satisfactorily as arising from a mixture consisting predominantly of monomers. In protic solvent (H2O, MeOH), the ECD spectra are consistent with H-bonded monomers. Simple modeling suggests that the rotational strengths of the first electronic transition gain most of their intensity from the nonplanarity of the amide chromophore, the contributions of which follow a spiral rule previously enunciated.

Optical Activity of Symmetric Compounds in Chiral Media. I. Induced Circular Dichroism of Unbound Substrates

1971 ◽  
Vol 49 (4) ◽  
pp. 624-631 ◽  
Author(s):  
L. D. Hayward ◽  
R. N. Totty
Keyword(s):  
Circular Dichroism ◽  
Carbonyl Compounds ◽  
Optical Rotation ◽  
Optically Active ◽  
Asymmetric Induction ◽  
Azo Compounds ◽  
Induced Circular Dichroism ◽  
Chiral Media ◽  
Circular Dichroïsm ◽  
Rotational Strengths

In the presence of chiral environment compounds, C, optical rotation is induced in symmetric substrates, S, and may be detected as circular dichroism in the electronic spectra of the solutions. Thus the n − π* transitions of symmetric and racemic carbonyl compounds, and of symmetric nitro and azo compounds, become optically active when these S are dissolved in chiral hydrocarbons, ketones, or carbinols, or in solutions of these C in achiral solvents. The rotational strengths of the induced circular dichroism bands of S are solvent, temperature, and concentration dependent. Only limited correlation of the sign and magnitude of the induced bands with the stereochemistry of C and S is evident on the data so far accumulated. Halogenated achiral solvents enhance the intensity, and, in some cases reverse the sign of the induced bands.A new mechanism of asymmetric induction is proposed in which specific bonding of C with S is not prerequisite.

scholarly journals Chiral All-Dielectric Metasurface Based on Elliptic Resonators with Circular Dichroism Behavior

2018 ◽  
Vol 2018 ◽  
pp. 1-7 ◽  
Author(s):  
Ali Yahyaoui ◽  
Hatem Rmili
Keyword(s):  
Circular Dichroism ◽  
Design Procedure ◽  
Design Parameters ◽  
Dielectric Resonators ◽  
Polarization Filter ◽  
Microwave Frequencies ◽  
Main Design ◽  
Circular Polarizer ◽  
Circular Dichroïsm ◽  
Dielectric Metasurface

We present the design of a new microwave all-dielectric chiral metasurface with circular dichroism behavior based on elliptic dielectric resonators (EDRs). During the design procedure, we have first optimized numerically the effects of the main design parameters such as the resonator’s size and orientation, as well as the size of the slot within them, on the metasurface transmission over the frequency band 10–20 GHz. Measurements on the final metasurface prototype have shown a large circular dichroism (Δ=0.61 and Δ=0.5) over two bands (17.55–17.61 GHz and 17.91–18.05 GHz) with ellipticities close to 45° which means that the developed device can be used as a circular polarization filter and circular polarizer at microwave frequencies.

scholarly journals Solvent Induced Circular Dichroism in Conformational Analysis: Bile Pigments

1981 ◽  
Vol 36 (6) ◽  
pp. 735-738 ◽  
Author(s):  
Harald Lehner ◽  
Corinna Krauss ◽  
Hugo Scheer
Keyword(s):  
Circular Dichroism ◽  
Conformational Analysis ◽  
The Other ◽  
Bile Pigments ◽  
Induced Circular Dichroism ◽  
Steric Strain ◽  
Order Of Magnitude ◽  
Circular Dichroïsm ◽  
Rotational Strengths ◽  
Related Compounds

Abstract The applicability of solvent induced circular dichroism (SICD) for the conformational analysis of bile pigments has been investigated. The S-(-)-ethyl lactate induced rotational strengths for octaethylbilindion (4) and its dihydroderivative 5 are remarkably high. Related compounds, e.g. the isomeric purpurines 1 and 2 and formyltripyrrinon 3 exhibit an optical activity which is smaller by more than one order of magnitude. 1-3 are essentially free from steric strain so that a flat arrangement of the chromophore is most likely. On the other hand the closed conformations of 4 and 5 experience considerable steric repulsion of their terminal rings, so that a helical topology is energetically favoured. This distinction is reflected in the magnitude of the SICD observed and demonstrates its applicability for the conformational analysis of bile pigments.

Circular dichroism spectra of asymmetric unidentate amine complexes of cobalt(III)

1973 ◽  
Vol 26 (11) ◽  
pp. 2401 ◽  
Author(s):  
CJ Hawkins ◽  
GA Lawrance
Keyword(s):  
Circular Dichroism ◽  
Absorption Band ◽  
Aromatic Compounds ◽  
Visible Region ◽  
The Other ◽  
Circular Dichroism Spectra ◽  
Alkyl Derivatives ◽  
Cotton Effects ◽  
Circular Dichroïsm ◽  
Rotational Strengths

The preparations of pentaamminecobalt(III) complexes of a series of asymmetric unidentate amines are reported. The circular dichroism spectra for the (S)-amines show negative Cotton effects under the 1A1g → 1T1g absorption band, which are somewhat solvent dependent but independent of temperature down to -190�C. The vicinal effect from 1- cyclohexylethylamine was comparable to that from analogous aromatic compounds, but the simpler alkyl derivatives were found to impose smaller rotational strengths on the d-d transitions. The lack of measurable c.d. in the visible region for tetraammine((S)-butane-1,3- diamine)cobalt(III) is reported and discussed in the light of the other studies.

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