The vibrational circular dichroism spectra of 2-methylaziridine: dominance of the asymmetric centre at nitrogen

1994 ◽  
Vol 72 (3) ◽  
pp. 506-513 ◽  
Author(s):  
Arvi Rauk ◽  
Thomas Eggimann ◽  
Helmut Wieser ◽  
Gennadii V. Shustov ◽  
Danya Yang
Keyword(s):  
Equilibrium Mixture ◽  
Vibrational Circular Dichroism ◽  
Basis Set ◽  
Quantum Mechanical ◽  
Coupling Theory ◽  
Similar Magnitude ◽  
Chiroptical Properties ◽  
Methyl Group ◽  
The Common ◽  
Cis And Trans

The experimental VCD spectrum of (2R)-2-methylaziridine has been measured in the region 800–1500 cm−1. The ab initio implementation of the Vibronic Coupling Theory (VCT) of Nafie and Freedman, using the 6-31G*(0.3) basis set, in the common origin and distributed origin gauges and with uniformly and optimally scaled quantum mechanical force fields, is used to investigate the chiroptical properties. VCD spectra are computed for both cis and trans invertomers. The predicted VCD spectrum of 2-methylaziridine (the equilibrium mixture) is dominated by that of the trans diastereomer, not simply because of its greater abundance but because the rotatory strengths of many absorptions in the mid-IR are oppositely signed and of similar magnitude in the two invertomers which differ in absolute configuration at nitrogen. The VCD spectrum of 2-methylaziridine is compared in detail to that of 2-methyloxirane. In the region of the methyl group deformations and CH2 scissor, the theoretical (R)-2-methyloxirane VCD spectrum displays a much closer similarity to the cis-(2R)-2-methylaziridine than to the trans diastereomer.

A conformational study of (1S, 2R, 5S)-( + )-menthol using vibrational circular dichroism spectroscopy

1998 ◽  
Vol 76 (3) ◽  
pp. 274-283 ◽  
Author(s):  
Jennifer L McCann ◽  
Arvi Rauk ◽  
Hal Wieser
Keyword(s):  
Circular Dichroism ◽  
Density Functional ◽  
Chair Conformation ◽  
Equilibrium Mixture ◽  
Vibrational Circular Dichroism ◽  
Basis Set ◽  
Hydroxyl Group ◽  
Functional Theory ◽  
Hartree Fock ◽  
Circular Dichroïsm

We report the experimental and predicted absorption and vibrational circular dichroism (VCD) spectra of (1S, 2R, 5S)-(+)-menthol. The harmonic force fields and atomic polar tensors (APTs) were obtained for 10 conformers using density functional theory (DFT) with the Becke3LYP functional and the 6-31G** basis set. The atomic axial tensors (AATs) were obtained with restricted Hartree-Fock (RHF) theory and a 6-31G basis set. VCD intensities were predicted from vibronic coupling theory (VCT). The predicted absorption and VCD spectra based on an equilibrium mixture of conformers corresponded well with the experimental spectra, indicating a reasonable geometry and frequency analysis for each of the conformers. The largest contributions towards the equilibrium population derive from conformers in which the cyclohexane ring occupies a chair conformation, the isopropyl group is directed away from the hydroxyl group, and only the hydroxyl group assumes different conformations.Key words: vibrational circular dichroism (VCD), menthol, conformational analysis.

The infrared spectrum of 2-methylaziridine from scaled abinitio force fields

1992 ◽  
Vol 70 (2) ◽  
pp. 464-477 ◽  
Author(s):  
Arvi Rauk ◽  
T. Eggimann ◽  
H. Wieser ◽  
Danya Yang
Keyword(s):  
Infrared Spectrum ◽  
Vapor Phase ◽  
Ir Spectrum ◽  
Force Fields ◽  
Experimental Spectrum ◽  
Equilibrium Mixture ◽  
Basis Set ◽  
Complete Assignment ◽  
Cis And Trans ◽  
Good Agreement

The structures of the cis and trans invertomers of 2-methylazirdine were optimized at the RHF/6-31G*(0.3) level of theory and the composition of the equilibrium mixture was determined to be trans/cis = 0.71:0.29, in good agreement with the experimental value, 0.66:0.35. The abinitio force field was scaled and a complete assignment of the vibrational spectra of the two conformers is presented. The IR spectrum of 2-methylazirdine was recorded in the vapor phase and in solution (cyclohexane and CCl4). The predicted IR spectrum of the equilibrium mixture agrees very well with the experimental spectrum. The 6-31G*(0.3) basis set is found to provide better geometries and more uniformly scalable force fields than the conventional 6-31G* basis set. Keywords: abinitio force fields, 2-methylaziridine.

scholarly journals Characterization of a Natural, Stable, Reversible and Colourful Anthocyanidin Network from Sphagnum Moss Based Mainly on the Yellow Trans-Chalcone and Red Flavylium Cation Forms

Molecules ◽  
2021 ◽  
Vol 26 (3) ◽  
pp. 709
Author(s):  
Helge Berland ◽  
Øyvind M. Andersen
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Cell Wall ◽  
Peat Moss ◽  
Sphagnum Moss ◽  
Naturally Occurring ◽  
Two Component ◽  
Colour System ◽  
The Common ◽  
Cis And Trans

Anthocyanins with various functions in nature are one of the most important sources of colours in plants. They are based on anthocyanidins or 3-deoxyanthocyanidins having in common a C15-skeleton and are unique in terms of how each anthocyanidin is involved in a network of equilibria between different forms exhibiting their own properties including colour. Sphagnorubin C (1) isolated from the cell wall of peat moss (Sphagnum sp.) was in fairly acidic and neutral dimethyl sulfoxide characterized by nuclear magnetic resonance (NMR) and ultraviolet–visible (UV–vis) absorption techniques. At equilibrium, the network of 1 behaved as a two–component colour system involving the reddish flavylium cationic and the yellow trans–chalcone forms. The additional D- and E-rings connected to the common C15-skeleton extend the π-conjugation within the molecule and provide both bathochromic shifts in the absorption spectra of the various forms as well as a low isomerization barrier between the cis- and trans-chalcone forms. The hemiketal and cis-chalcone forms were thus not observed experimentally by NMR due to their short lives. The stable, reversible network of 1 with good colour contrast between its two components has previously not been reported for other natural anthocyanins and might thus have potential in future photochromic systems. This is the first full structural characterization of any naturally occurring anthocyanin chalcone form.

scholarly journals Crystal structure of a new monoclinic polymorph ofN-(4-methylphenyl)-3-nitropyridin-2-amine

2014 ◽  
Vol 70 (8) ◽  
pp. 58-61
Author(s):  
Aina Mardia Akhmad Aznan ◽  
Zanariah Abdullah ◽  
Vannajan Sanghiran Lee ◽  
Edward R. T. Tiekink
Keyword(s):  
Three Dimensional ◽  
Basis Set ◽  
Dihedral Angles ◽  
Asymmetric Unit ◽  
Acta Cryst ◽  
Common Features ◽  
Compound C ◽  
B3lyp Level ◽  
The Common ◽  
Independent Molecules

The title compound, C12H11N3O2, is a second monoclinic polymorph (P21, withZ′ = 4) of the previously reported monoclinic (P21/c, withZ′ = 2) form [Akhmad Aznanet al.(2010).Acta Cryst.E66, o2400]. Four independent molecules comprise the asymmetric unit, which have the common features of asyndisposition of the pyridine N atom and the toluene ring, and an intramolecular amine–nitro N—H...O hydrogen bond. The differences between molecules relate to the dihedral angles between the rings which range from 2.92 (19) to 26.24 (19)°. The geometry-optimized structure [B3LYP level of theory and 6–311 g+(d,p) basis set] has the same features except that the entire molecule is planar. In the crystal, the three-dimensional architecture is consolidated by a combination of C—H...O, C—H...π, nitro-N—O...π and π–π interactions [inter-centroid distances = 3.649 (2)–3.916 (2) Å].

Net charges and valence AO's in the methylamines; the hydrogen basis set and the properties of nitrogen

1985 ◽  
Vol 63 (7) ◽  
pp. 1487-1491 ◽  
Author(s):  
Giuseppe Del Re ◽  
Sándor Fliszár ◽  
Michel Comeau ◽  
Claude Mijoule
Keyword(s):  
Basis Set ◽  
Basis Sets ◽  
Methyl Groups ◽  
Extended Form ◽  
Amine Nitrogen ◽  
Methyl Group ◽  
Net Charges ◽  
Extended Basis

Net charges and valence AO's for ammonia, methylamine, dimethylamine, and trimethylamine were calculated using extended basis sets. Superposition effects, evaluated by replacing Pople's standard 6-31G* basis by an extended form in which the basis of the ammonia H atoms and of the methyl groups of trimethylamine are retained in the treatment of each molecule, indicate that the quality of the treatment of amine nitrogen atoms is strongly dependent on the number of methyl groups. A new, augmented basis is proposed for the hydrogens, which appears to be reasonably well balanced: comparison with familiar (e.g., 6-31G*) calculations illustrates in what manner the treatment of nitrogen is worsened when even just one methyl group is replaced by hydrogen unless the impoverishment of the basis is suitably taken care of.

Some volatile constituents of terrestrial slaters

1966 ◽  
Vol 19 (8) ◽  
pp. 1495 ◽  
Author(s):  
GWK Cavill ◽  
DV Clark ◽  
H Hinterberger
Keyword(s):  
Porcellio Scaber ◽  
Volatile Constituents ◽  
The Common ◽  
Cis And Trans ◽  
Unsaturated Component

The common terrestrial dater, Porcellio scaber, yields a volatile extractive, slaterol, which comprises cis- and trans-dec-3-en-1-ol (80%), together with cis- and trans-non-3-en-1-ol and nonan-1-ol (5%). The remaining and unsaturated component of slaterol (A, 15%), which gives decan-1-ol on reduction, has yet to be characterized. An undescribed Armadillidium sp. yields a single constituent, octan-1-ol.

The role of the basis set and the level of quantum mechanical theory in the prediction of the structure and reactivity of cisplatin

2012 ◽  
Vol 33 (29) ◽  
pp. 2292-2302 ◽  
Author(s):  
Diego Paschoal ◽  
Bruna L. Marcial ◽  
Juliana Fedoce Lopes ◽  
Wagner B. De Almeida ◽  
Hélio F. Dos Santos
Keyword(s):  
Basis Set ◽  
Quantum Mechanical ◽  
Mechanical Theory ◽  
Quantum Mechanical Theory
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