Ab initio DFT calculations of the configurational and conformational preferences of 2-phenylsulfinylcyclohexanones — Evidence for "exo-anomeric" interactions

2006 ◽  
Vol 84 (4) ◽  
pp. 685-691 ◽  
Author(s):  
Melissa L Trapp ◽  
John F Wojcik ◽  
Walter W Zajac, Jr. ◽  
B Mario Pinto
Keyword(s):  
Dft Calculations ◽  
Ab Initio ◽  
High Energy ◽  
The Other ◽  
Carbonyl Carbon Atom ◽  
Torsional Angle ◽  
Orbital Interaction ◽  
Anomeric Effect ◽  
Orbital Interactions ◽  
Conformational Preferences

The conformational analysis of 2-phenylsulfinylcyclohexanone by ab initio density functional calculations is described. Six conformations corresponding to axial/equatorial isomers and rotation about the exocyclic C2—S bond in each of the RR or RS diastereomers were calculated and the results were examined in terms of relative energies, electrostatic interactions, orbital interactions, and geometrical variations. The global minimum conformation was the RS isomer that positioned the phenylsulfinyl moiety in an equatorial orientation and the sulfinyl oxygen in an anti orientation with respect to the carbonyl carbon atom. Of the other three low energy conformations, only one had a gauche arrangement of these atoms, and only in one of the four lower energy conformations was evidence found for a S-O(–)···C(+)-O electrostatic interaction. In contrast, the results were consistent with the operation of nS → [Formula: see text] stabilizing orbital interactions. Further support for this hypothesis was obtained from the increased C=O bond lengths in these four conformations relative to the other conformations, and by the torsional angle distortion away from ideal geometry, presumably to maximize the stabilizing orbital interaction. We propose that this conformational preference is a manifestation of a generalized exo-anomeric effect. The longer C2—S bond in the axial isomers was also interpreted in terms of a stabilizing πC=O → [Formula: see text] interaction, analogous to an endo-anomeric interaction. Comparison of the computational results to available experimental data on the conformational equilibrium of each diastereomer in solution suggests which conformers are present in each of the equilibria. The available data for the solid state indicate that the RR and RS isomers both crystallize in high energy conformations, stabilized by intermolecular interactions.Key words: 2-phenylsulfinylcyclohexanones, configurational isomers, conformational preferences, DFT calculations, exo-anomeric effect.

Conformational Preferences of Ethyl 2,3-Dideoxy-3-[(α-D-glucopyranosyl)methyl]-β-L- and -D-arabino-hexopyranosides

2005 ◽  
Vol 70 (12) ◽  
pp. 2086-2100 ◽  
Author(s):  
Ondřej Vích ◽  
Ladislav Kniežo ◽  
Hana Dvořáková ◽  
Ivan Raich ◽  
Štěpán Valenta
Keyword(s):  
The Other ◽  
Glycosidic Bond ◽  
Conformational Behavior ◽  
Anomeric Effect ◽  
Conformational Preference ◽  
Other Hand ◽  
Conformational Preferences

Conformational behavior of two C-disaccharides, containing D-glucopyranose moiety at the non-reducing end and L- or D-2-deoxy-arabino-hexopyranose moiety at the reducing end, has been studied using MM3 calculations and NMR experiments. The obtained results show that the conformational preference around the C-glycosidic bond is the same in both compounds and corresponds with the exo-anomeric effect. On the other hand, both compounds differ markedly in the conformational arrangement around the C-aglycone bond where the population of conformers is controlled by 1,3-diaxial-like interactions.

The intriguing question of anionic redox in high-energy density cathodes for Li-ion batteries

2016 ◽  
Vol 9 (3) ◽  
pp. 984-991 ◽  
Author(s):  
M. Saubanère ◽  
E. McCalla ◽  
J.-M. Tarascon ◽  
M.-L. Doublet
Keyword(s):  
Energy Density ◽  
Dft Calculations ◽  
First Principles ◽  
High Energy ◽  
High Energy Density ◽  
Atomic Charges ◽  
Li Ion Batteries ◽  
Redox Mechanism ◽  
Orbital Interactions ◽  
Li Ion

This paper aims to identify robust descriptors to rationalize the anionic redox mechanism in layered Li-rich TM-oxides using conceptual tools, such as atomic charges, orbital interactions and crystal orbital overlap populations (COOP), based on first-principles DFT calculations.

Concerning the conformational preferences of the 2-cyano derivatives of oxane, thiane, and selenane

2010 ◽  
Vol 88 (8) ◽  
pp. 831-838 ◽  
Author(s):  
Michael H. Benn ◽  
Yan Yan Huang ◽  
Frank Johannsen ◽  
Michael O’Reilly ◽  
Masood Parvez ◽  
...  
Keyword(s):  
Bond Length ◽  
Cyano Group ◽  
Lone Pair ◽  
Nbo Analysis ◽  
Orbital Interaction ◽  
Anomeric Effect ◽  
Model Compounds ◽  
Conformational Preferences ◽  
Lone Pair Electrons ◽  
Derivatives Of

This paper investigates the origin of the anomalous anomeric effect in merosinigrin, a 2-cyanothiane in which the cyano group is axial as expected for the anomeric effect, but in which bond distances are opposite to that expected from the nS→[Formula: see text] orbital interaction, which underlies the classical anomeric effect. The model compounds, 2-cyanooxane, 2-cyanothiane, and 2-cyanoselenane, were synthesized and studied both experimentally and computationally. Both the thia and selena systems displayed an even higher preference for the axial conformation than the oxa system but also exhibited the bond length anomalies found previously in merosinigren. Natural bond order (NBO) analysis of the B3LYP/6–311+G(3df,2p) wave functions of the axial and equatorial forms of the three systems confirmed a weakening of the n→σ* orbital interaction in the O, S, and Se series, and a strengthening of a σ–π*(CN) interaction that explains the bond length reversals observed in the S and Se systems. It also revealed a new mechanism, n→π*, namely, a through-space interaction between the nonbonded lone pair electrons of the heteroatom and the π* orbital of the cyano group, which selects for the axial conformation.

An exploratory ab initio study on the conformations of ethylguanidine in its neutral [CH3-CH2-NH-C(=NH)NH2] and protonated [CH3-CH2-NH-C(NH2)2] forms

2000 ◽  
Vol 78 (5) ◽  
pp. 626-641 ◽  
Author(s):  
Melody L Mak ◽  
Salvatore J Salpietro ◽  
R Daniel Enriz ◽  
Imre G Csizmadia
Keyword(s):  
Dft Calculations ◽  
Conformational Analysis ◽  
Ab Initio ◽  
Internal Symmetry ◽  
Basis Sets ◽  
Side Chain ◽  
Torsional Angle ◽  
Ab Initio Study ◽  
Single Isomer ◽  
Arginine Side Chain

To explore the conformation intricacies of the guanidine group in the arginine side chain, ab initio computations have been carried out with ethylguanidine and the ethyl guanidinium ion. HF computations have been performed using 3-21G and 6-31G basis sets and DFT calculations were carried out at the B3LYP/6-31G(d) level of theory. The ethyl guanidinium ion has a single isomer due to its internal symmetry, although this structure has at least three conformations. However, several structures were found and optimized for ethylguanidine, involving the endo- and exo- orientation of the lone NH and torsional angle χ6, as well as the torsional modes associated with χ4 and χ5. Torsional angle χ5 gives rise to s-cis and s-trans structures.Key words: ethylguanidine, ethylguanidinium ion, ab initio MO, arginine side-chain, conformational analysis.

Lone pair interactions in dimethoxymethane and anomeric effect

1979 ◽  
Vol 57 (4) ◽  
pp. 424-435 ◽  
Author(s):  
Igor Tvaroška ◽  
Tomaš Bleha
Keyword(s):  
Lone Pair ◽  
Theoretical Interpretation ◽  
Orbital Interaction ◽  
Anomeric Effect ◽  
Gauche Conformation ◽  
Orbital Interactions ◽  
Dipole Interactions ◽  
Lone Pairs ◽  
Molecular Orbital Analysis ◽  
P Type

Perturbation molecular orbital analysis has been used for a computation of the through-bond and through-space orbital interactions of oxygen lone pairs in dimethoxymethane (DMM). The analysis predicts the symmetrical combination of p-type lone pairs as a highest occupied orbital in an antiperiplanar conformation. The conformational dependence of through-bond orbital interactions has the character of the V2 term in the Fourier expansion of the rotation potential function about the C—O bond. Contrary to the recent theoretical interpretation that the anomeric effect (preference of gauche conformation) is caused by superjacent orbital control, the orbital interactions in DMM are not dominant terms with respect to the anomeric or exoanomeric effect. The dipole–dipole interactions of the C—O bonds stabilizing the gauche conformation should thus be considered as the primary cause of the anomeric effect in DMM. The frontier orbital energies and geometric parameters in DMM are strongly influenced by a variation of orbital interaction with rotation. Results obtained for DMM are used to explain the conformational behaviour of other molecules containing the acetal moiety, such as pyrane heterocycles, sugars, and polyoxymethylene.

pKa of Organoselenium Compounds: Ab Initio and DFT Calculations

2007 ◽  
Author(s):  
Sajjad Karamat ◽  
Juraj Kona ◽  
Walter Fabian
Keyword(s):  
Dft Calculations ◽  
Ab Initio ◽  
Organoselenium Compounds ◽  
Ab Initio And Dft

FT-IR, FT-Raman spectra and ab initio HF and DFT calculations of 4-N,N′-dimethylamino pyridine

2008 ◽  
Vol 71 (3) ◽  
pp. 898-906 ◽  
Author(s):  
N. Sundaraganesan ◽  
S. Kalaichelvan ◽  
C. Meganathan ◽  
B. Dominic Joshua ◽  
J. Cornard
Keyword(s):  
Dft Calculations ◽  
Ab Initio ◽  
Raman Spectra ◽  
Ft Ir ◽  
Hf And Dft Calculations ◽  
Ab Initio Hf ◽  
Ft Raman

ChemInform Abstract: Ab initio Calculations on Al2N4 and AlNn (n = 4 to 7): Potential Precursors of High Energy Density Materials.

ChemInform ◽  
2010 ◽  
Vol 33 (47) ◽  
pp. no-no
Author(s):  
Edmond P. F. Lee ◽  
John M. Dyke ◽  
Rob P. Claridge
Keyword(s):  
Energy Density ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
High Energy ◽  
High Energy Density ◽  
High Energy Density Materials

High Energy Local Vibrational Modes of Carbon Aggregates in SiC: Experimental and Theoretical Insight

2006 ◽  
Vol 527-529 ◽  
pp. 465-468 ◽  
Author(s):  
Alexander Mattausch ◽  
M. Bockstedte ◽  
Oleg Pankratov ◽  
John W. Steeds ◽  
S.A. Furkert ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
High Energy ◽  
Vibrational Modes ◽  
Energy Mode ◽  
Local Vibrational Modes ◽  
Theoretical Insight

We observe new photoluminescence centers in electron-irradiated 6H-SiC with phonon replicas up to 250 meV and clear threefold isotope splitting of the highest energy mode. Based on ab initio calculations, we discuss the tri-carbon anti-site (C3)Si and the di-interstitial (C2)Hex as models for these centers.

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