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.

scholarly journals Expression and interactions of stereochemically active lone pairs and their relation to structural distortions and thermal conductivity

IUCrJ ◽  
2020 ◽  
Vol 7 (3) ◽  
pp. 480-489 ◽  
Author(s):  
Kasper Tolborg ◽  
Carlo Gatti ◽  
Bo B. Iversen
Keyword(s):  
Thermal Conductivity ◽  
Density Functional ◽  
Lone Pair ◽  
Density Functional Theory Calculations ◽  
Orbital Interaction ◽  
Void Space ◽  
Metal Compounds ◽  
Bond Angles ◽  
Lone Pairs ◽  
Bonding Effect

In chemistry, stereochemically active lone pairs are typically described as an important non-bonding effect, and recent interest has centred on understanding the derived effect of lone pair expression on physical properties such as thermal conductivity. To manipulate such properties, it is essential to understand the conditions that lead to lone pair expression and provide a quantitative chemical description of their identity to allow comparison between systems. Here, density functional theory calculations are used first to establish the presence of stereochemically active lone pairs on antimony in the archetypical chalcogenide MnSb2O4. The lone pairs are formed through a similar mechanism to those in binary post-transition metal compounds in an oxidation state of two less than their main group number [e.g. Pb(II) and Sb(III)], where the degree of orbital interaction (covalency) determines the expression of the lone pair. In MnSb2O4 the Sb lone pairs interact through a void space in the crystal structure, and their their mutual repulsion is minimized by introducing a deflection angle. This angle increases significantly with decreasing Sb—Sb distance introduced by simulating high pressure, thus showing the highly destabilizing nature of the lone pair interactions. Analysis of the chemical bonding in MnSb2O4 shows that it is dominated by polar covalent interactions with significant contributions both from charge accumulation in the bonding regions and from charge transfer. A database search of related ternary chalcogenide structures shows that, for structures with a lone pair (SbX 3 units), the degree of lone pair expression is largely determined by whether the antimony–chalcogen units are connected or not, suggesting a cooperative effect. Isolated SbX 3 units have larger X—Sb—X bond angles and therefore weaker lone pair expression than connected units. Since increased lone pair expression is equivalent to an increased orbital interaction (covalent bonding), which typically leads to increased heat conduction, this can explain the previously established correlation between larger bond angles and lower thermal conductivity. Thus, it appears that for these chalcogenides, lone pair expression and thermal conductivity may be related through the degree of covalency of the system.

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.

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.

Driving Force Behind the O-Rh(001) Clock Reconstruction

1998 ◽  
Vol 12 (20) ◽  
pp. 849-857 ◽  
Author(s):  
Chang Q. Sun
Keyword(s):  
Driving Force ◽  
Electrostatic Force ◽  
Bond Formation ◽  
Lone Pair ◽  
Atomic Ratio ◽  
Recent Model ◽  
Dual Roles ◽  
Low Energy Electron Diffraction ◽  
Dipole Interactions ◽  
Low Energy Electron

A novel rhombi-chain network is derived from low energy electron diffraction experimental observations and the recent model theory, revealing that the O-Rh(100) clock-rotation is driven by an electrostatic force arisen from bond formation. Thus the O-Rh bond suffers from tension other than compression, or strain relief. As O -1 evolves into the hybridized- O -2,a Rh 5 O cluster in the c(2 × 2) phase develops into a Rh 4 O tetrahedron and yields the overall (2 × 2)p4g reconstruction. In the (2 × 2)p4g phase, the hollow-sited O -2 defines one Rh + ion and two lone-pair-induced Rh dipoles of its four surface neighbors. The surface atomic ratio (O : Rh = 1 : 2) allocates, therefore, half of the surface Rh atoms to be the Rh dipoles and another half to play dual roles of Rh + ion and Rh dipole. Interactions along the "dipole–dipole – Rh +/dipole – Rh +/dipole" strings create the rhombi-chain at the <11> directions, and a responding bond tension confines the (2 × 2)p4g clock rotation.

Theoretical perspective of the lone pair activity influence on band gap and SHG response of lead borates

RSC Advances ◽  
2015 ◽  
Vol 5 (97) ◽  
pp. 79882-79887 ◽  
Author(s):  
Danni Li ◽  
Qun Jing ◽  
Chen Lei ◽  
Shilie Pan ◽  
Bingbing Zhang ◽  
...  
Keyword(s):  
Band Gap ◽  
Theoretical Perspective ◽  
Lone Pair ◽  
Red Shift ◽  
Lone Pairs

Metal lone pairs play an important role in determining the SHG enhancement and bandgap red shift.

Anomalous stabilizing and destabilizing effects in some cyclic π-electron systems

1993 ◽  
Vol 71 (8) ◽  
pp. 1123-1127 ◽  
Author(s):  
Peter Politzer ◽  
M. Edward Grice ◽  
Jane S. Murray ◽  
Jorge M. Seminario
Keyword(s):  
Ab Initio ◽  
Lone Pair ◽  
Electrostatic Potentials ◽  
Electron Delocalization ◽  
Isodesmic Reaction ◽  
Computational Studies ◽  
Electron Systems ◽  
Molecular Electrostatic Potentials ◽  
Lone Pairs

Ab initio computational studies have been carried out for three molecules that are commonly classed as antiaromatic: cyclobutadiene (1), 1,3-diazacyclobutadiene (7), and 1,4-dihydropyrazine (6). Their dinitro and diamino derivatives were also investigated. Stabilizing or destabilizing energetic effects were quantified by means of the isodesmic reaction procedure at the MP2/6-31G*//HF/3-21G level, and calculated molecular electrostatic potentials (HF/STO-5G//HF/3-21G) were used as a probe of electron delocalization. Our results do not show extensive delocalization in the π systems of any one of the three parent molecules. The destabilization found for 1 and 7 is attributed primarily to strain and to repulsion between the localized π electrons in the C=C and C=N bonds, respectively. However, 6 is significantly stabilized, presumably due to limited delocalization of the nitrogen lone pairs. NH2 groups are highly stabilizing, apparently because of lone pair delocalization. NO2 is neither uniformly stabilizing nor destabilizing.

p-Type conductivity of GeTe: The role of lone-pair electrons

2012 ◽  
Vol 249 (10) ◽  
pp. 1902-1906 ◽  
Author(s):  
Alexander V. Kolobov ◽  
Paul Fons ◽  
Junji Tominaga
Keyword(s):  
Lone Pair ◽  
Type Conductivity ◽  
P Type ◽  
Lone Pair Electrons

scholarly journals Sonochemical Reaction of Bifunctional Molecules on Silicon (111) Hydride Surface

Molecules ◽  
2021 ◽  
Vol 26 (20) ◽  
pp. 6166
Author(s):  
Serge Ismael Zida ◽  
Yue-Der Lin ◽  
Yit Lung Khung
Keyword(s):  
Photoelectron Spectroscopy ◽  
Lone Pair ◽  
Thermal Reaction ◽  
Silicon Hydride ◽  
Force Microscopy ◽  
Bifunctional Molecules ◽  
Bond Breakage ◽  
Sonochemical Reaction ◽  
Grafting From ◽  
P Type

While the sonochemical grafting of molecules on silicon hydride surface to form stable Si–C bond via hydrosilylation has been previously described, the susceptibility towards nucleophilic functional groups during the sonochemical reaction process remains unclear. In this work, a competitive study between a well-established thermal reaction and sonochemical reaction of nucleophilic molecules (cyclopropylamine and 3-Butyn-1-ol) was performed on p-type silicon hydride (111) surfaces. The nature of surface grafting from these reactions was examined through contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Cyclopropylamine, being a sensitive radical clock, did not experience any ring-opening events. This suggested that either the Si–H may not have undergone homolysis as reported previously under sonochemical reaction or that the interaction to the surface hydride via a lone-pair electron coordination bond was reversible during the process. On the other hand, silicon back-bond breakage and subsequent surface roughening were observed for 3-Butyn-1-ol at high-temperature grafting (≈150 °C). Interestingly, the sonochemical reaction did not produce appreciable topographical changes to surfaces at the nano scale and the further XPS analysis may suggest Si–C formation. This indicated that while a sonochemical reaction may be indifferent towards nucleophilic groups, the surface was more reactive towards unsaturated carbons. To the best of the author’s knowledge, this is the first attempt at elucidating the underlying reactivity mechanisms of nucleophilic groups and unsaturated carbon bonds during sonochemical reaction of silicon hydride surfaces.

Rabbit ears concepts of water lone pairs: a reply to comments of Hiberty, Danovich, and Shaik

2015 ◽  
Vol 16 (3) ◽  
pp. 694-696 ◽  
Author(s):  
A. D. Clauss ◽  
M. Ayoub ◽  
J. W. Moore ◽  
C. R. Landis ◽  
F. Weinhold
Keyword(s):  
Lone Pair ◽  
Lone Pairs ◽  
Rabbit Ears

We respond to recent comments (Hibertyet al., 2015) on our earlier article (Clausset al., 2014) concerning “rabbit ears” depictions of lone pair orbitals in water and other species.

A new insight into π–π stacking involving remarkable orbital interactions

2016 ◽  
Vol 18 (36) ◽  
pp. 25452-25457 ◽  
Author(s):  
Rundong Zhao ◽  
Rui-Qin Zhang
Keyword(s):  
Orbital Interaction ◽  
Orbital Interactions ◽  
Π Interactions ◽  
Π Stacking ◽  
Unified Description ◽  
Insight Into

The importance of orbital interaction in π–π interactions is explored in detail and a unified description of π–π stacking is proposed.

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