The gauche effect on conformation. α-Substituted sulfones and N-substituted sulfonamides

1979 ◽  
Vol 44 (11) ◽  
pp. 3378-3384 ◽  
Author(s):  
Otto Exner ◽  
Jan B. F. N. Engberts
Keyword(s):  
Lone Electron Pair ◽  
Electron Pair ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Conformational Preference ◽  
Electron Pairs ◽  
Gauche Effect

The dipole moments of α-halogenosulfones IIa-f in benzene solution revealed the conformation C, those of N-methyl-N-nitrosulfonamides IIIa-c the conformation F. In either case the conformational preference is governed by the gauche rule which may be worded in a modified version that symmetrical positions of polar bonds and/or of lone electron pairs are disfavoured. A lone electron pair appears to be more significant than a polar bond.

Studies on bond and atomic valences. I. correlation between bond valence and bond angles in SbIII chalcogen compounds: the influence of lone-electron pairs

1996 ◽  
Vol 52 (1) ◽  
pp. 7-15 ◽  
Author(s):  
X. Wang ◽  
F. Liebau
Keyword(s):  
Statistical Analysis ◽  
Valence State ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Bond Valence ◽  
Continuous Change ◽  
Oxidation Number ◽  
Electron Pairs ◽  
Atomic Valence ◽  
Bond Valence Parameter

In the present bond-valence concept the bond-valence parameter ro is treated as constant for a given pair of atoms, and it is assumed that the bond valence sij is a function of the corresponding bond length Dij , and that the atomic valence is an integer equal to the formal oxidation number for Vi derived from stoichiometry. However, from a statistical analysis of 76 [SbIIIS n ] and 14 [SbIIISe n ] polyhedra in experimentally determined structures, it is shown that for SbIII—X bonds (X = S, Se), ro is correlated with {\bar \alpha} i , the average of the X—Sb—X angles between the three shortest Sb—X bonds. This is interpreted as a consequence of a progressive retraction of the 5s lone-electron pair from the SbIII nucleus, which can be considered as continuous change of the actual atomic valence act Vi of Sb from +3 towards +5. A procedure is derived to calculate an effective atomic valence eff Vi of SbIII from the geometry, {\bar \alpha} i and Dij , of the [SbIII Xn ] polyhedra, which approximates act Vi and is a better description of the actual valence state of SbIII than the formal valence for Vi . Calculated eff V SbIII are found to vary between +2.88 and +3.80 v.u. for [SbIIIS n ] and between +2.98 and +3.88 v.u. for [SbIIISe n ] polyhedra. It is suggested that a corresponding modification of the present bond-valence concept is also required for other cations with lone-electron pairs.

Spatial dispersion of lone electron pairs? – Experimental charge density of cubic arsenic(iii) oxide

2015 ◽  
Vol 17 (16) ◽  
pp. 11020-11027 ◽  
Author(s):  
Piotr A. Guńka ◽  
Zygmunt Gontarz ◽  
Janusz Zachara
Keyword(s):  
Charge Density ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Spatial Dispersion ◽  
Electron Pairs ◽  
First Time ◽  
Experimental Charge Density

Lone electron pair dispersion into three separate domains in space is reported and discussed for the first time.

Dipole moments and conformation of α-disulphones. The gauche effect

1985 ◽  
Vol 50 (10) ◽  
pp. 2245-2251 ◽  
Author(s):  
Otto Exner ◽  
Václav Jehlička
Keyword(s):  
Dihedral Angle ◽  
Graphical Method ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Statistical Treatment ◽  
X Ray ◽  
Gauche Effect

The dipole moments of substituted diphenyl disulphones I-III were measured in benzene solution and interpreted by the previously described graphical method. The results suggest an equilibrium of the ap and sc conformations in the ratio 3 : 1, at variance with various empirical rules and theories of the so-called gauche effect. A statistical treatment of X-ray data of various sulphonyl derivatives revealed essentially two preferred conformations: the more stable sc, with a broadened dihedral angle, and the less stable ap.

Conformational Analysis of Trimethylene Sulfites. The Importance of Vicinal Unshared Electron Pairs

1971 ◽  
Vol 49 (8) ◽  
pp. 1202-1208 ◽  
Author(s):  
Gordon Wood ◽  
John M. McIntosh ◽  
Maurice H. Miskow
Keyword(s):  
Conformational Analysis ◽  
Electron Pair ◽  
Dipole Moments ◽  
General Scheme ◽  
The Other ◽  
Ultrasonic Absorption ◽  
Electron Pairs ◽  
Alkyl Derivatives ◽  
Available Information ◽  
Rule Out

Dipole moments are reported for trimethylene sulfite and 11 alkyl derivatives in a variety of solvents (C6H12, CCl4, C6H6, dioxan). The variation of dipole moment with solvent for one of the 5-t-butyltrimethylene sulfite isomers is confirmed, but this behavior is not shown by the other compounds. This latter fact is used to rule out rapid chair–chair interconversion for these compounds. Recent ultrasonic absorption experiments are reinterpreted in the context of vicinal electron pair interactions and their effect on conformational analysis of sulfites and similar six-membered compounds. The result is a general scheme which is consistent with available information and which we believe is preferable to analysis of these compounds by analogy with cyclohexane.

Nonlinear optical ASnX (A = Na, H; X = N, P) nanosheets with divalent tin lone electron pair effect by first-principles design

Nanoscale ◽  
2020 ◽  
Vol 12 (27) ◽  
pp. 14895-14902
Author(s):  
Shengzi Zhang ◽  
Lei Kang ◽  
Zheshuai Lin
Keyword(s):  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
First Principles ◽  
Nonlinear Optical ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Second Harmonic ◽  
Electron Pairs ◽  
Divalent Tin

Divalent tin Sn2+ lone electron pairs can induce strong second harmonic generation density in 2D NaSnP and HSnN structures.

The Relative Orientation of the Total Dipole Moment in the N-cis Lone-Electron-Pair-Trans Isomer of Allylamine

1980 ◽  
Vol 35 (4) ◽  
pp. 415-417 ◽  
Author(s):  
Edmund Fischer ◽  
Ivan Botskor
Keyword(s):  
Dipole Moment ◽  
Trans Isomer ◽  
Large Amplitude ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Dipole Moments ◽  
Relative Orientation ◽  
Total Dipole Moment ◽  
Principal Axes ◽  
Large Amplitude Motions

Abstract The dipole moment of the doubly deuterated species (CH2=CH-CH2-ND2) of N-cis Lone-electron-pair isomer of allylamine has been measured. The "isotope pulling elfect" has been used to determine the relative orientation of the total dipole moment with respect to the principal axes in the normal species. The possible effects of large amplitude motions on the observed effective dipole moments are discussed.

The Contribution To Bond Valences By Lone Electron Pairs

2004 ◽  
Vol 848 ◽  
Author(s):  
Xiqu Wang ◽  
Friedrich Liebau
Keyword(s):  
Coordination Sphere ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Lone Pair ◽  
Bond Valence ◽  
Alkali Cations ◽  
Continuous Increase ◽  
Electron Pairs ◽  
Effective Valence

ABSTRACTBond valence sums (BVS) calculated for lone-pair cations are found increasingly higher than their formal valences as the retraction of the lone electron pair (LEP) from the nucleus is more pronounced. The increase in BVS is interpreted as a continuous increase of an effective valence of an atom that is a measure of its actual ability to bind other atoms without changing its formal valence. How the LEP of a lone-pair cation affects the effective valence of other atoms in a structure is studied by bond valence calculations for specific structures. For structures rich in alkali cations, it is found that the high effective valence of the lone-pair cations tends to be balanced by low effective valence of alkali cations. The LEP transfers bonding power or effective valence from the alkali cations to the lone-pair cations by joining the coordination sphere of the alkali cations.

Colloidal platinum sols: anion effects on coagulation behaviour

1983 ◽  
Vol 36 (11) ◽  
pp. 2163 ◽  
Author(s):  
DN Furlong ◽  
WHF Sasse
Keyword(s):  
Lone Electron Pair ◽  
Electron Pair ◽  
Electron Pairs ◽  
Anion Adsorption ◽  
Platinum Surfaces ◽  
Colloidal Platinum ◽  
Sol Stability

The concentration of added electrolyte required to induce coagulation of a platinum sol has been determined for a range of electrolytes. It has been found that, for electrolytes in which the anion contains lone-electron-pair substituents, sol stability is significantly enhanced compared with that observed when similar but non-electron-pair-containing anions are used. It is proposed that the lone electron pairs enable anion adsorption on negative platinum surfaces despite the Coulombic repulsions present.

The gauche Effect. A Theoretical Study of the Topomerization (Degenerate Racemization) and Tautomerization of Methoxide Ion Tautomer

1973 ◽  
Vol 51 (15) ◽  
pp. 2423-2432 ◽  
Author(s):  
Saul Wolfe ◽  
Luis M. Tel ◽  
I. G. Csizmadia
Keyword(s):  
Electronic State ◽  
Ground Electronic State ◽  
Conformational Transformation ◽  
Molecular Orbital Calculations ◽  
Rotational Angle ◽  
Electron Pairs ◽  
Hydroxyl Proton ◽  
Gauche Effect ◽  
Internuclear Distances ◽  
Relationship Of

Non-empirical double zeta quality molecular orbital calculations on −CH2OH as a function of the C—O bond length (r), the rotational angle about the C—O bond (θ), and the pyramidal angle at carbon [Formula: see text] are described. From the stretching potential curve, E(r), it is shown that dissociation of −CH2OH proceeds to give CH2 and OH−. The rotation–inversion surface, [Formula: see text], has two types of minima; in both cases the most favorable pyramidal angle at carbon is 105°. The lower minimum corresponds to a structure (the Y conformation) having the hydroxyl proton on the external bisector of the HCH angle. The higher minimum is 6.67 kcal/mol less stable and corresponds to a structure (the W conformation) having the hydroxyl proton on the internal bisector of the HCH angle. The relationship of these results to the gauche effect is discussed and it is noted that at certain internuclear distances the nuclear–nuclear repulsion term (Enucl) may overcome the tendency of adjacent electron pairs and polar bonds to exist preferentially in that conformation which has the maximum number of gauche interactions between these electron pairs or polar bonds.The topomerization of −CH2OH, i.e., the conformational transformation from one Y conformation into another, proceeds, via the W conformation as an intermediate, by two separate events, viz. rotation about the C—O bond, having a barrier of 10.58 kcal/mol, and pyramidal inversion at carbon, with a barrier of 20.52 kcal/mol. Some factors governing the relative importance of rotation and inversion in degenerate racemization are discussed.In its ground electronic state CH3O− is 22.18 kcal/mol more stable than −CH2OH. However, in the low-lying excited states all conformations of −CH2OH are stabilized relative to CH3O−. The most stable excited state structure of −CH2OH corresponds to the energy maximum for rotation–inversion of the ground electronic state.

Synthesis, Electronic Structure and Anti-Cancer Activity of the Phenyl Substituted Pyrazolo[1,5-a][1,3,5]triazines

2021 ◽  
Vol 25 ◽  
Author(s):  
Evgenia S. Veligina ◽  
Nataliya V. Obernikhina ◽  
Stepan G. Pilyo ◽  
Oleksiy D. Kachkovsky ◽  
Volodymyr S. Brovarets
Keyword(s):  
Electronic Transition ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Anti Cancer ◽  
Protein Molecules ◽  
Biological Affinity ◽  
Cancer Types ◽  
Derivatives Of ◽  
Cancer Activity

: Background: Synthesis of a series of 2-(dichloromethyl)pyrazolo[1,5- a][1,3,5]triazines was carried out and evaluated in vitro for their anticancer activity against a panel of 60 cell lines derived from nine cancer types. The joint quantum-chemical and experimental study of the influence of the extended πconjugated phenyl substituents on the electron structure of the pyrazolo[1,5-a][1,3,5]triazines as Pharmacophores were performed. It is shown that the decrease in the barriers to the rotation of phenyl substituents in compounds 1-7 possibly leads to an increase in the anti-cancer activity, which is in agreement with the change in the parameter biological affinity ϕ0. Analysis of the S0 → S1 electronic transitions (π→π*) of the pyrazolo[1,5-a][1,3,5]triazines shows that an increase in their intensity correlates with anti-cancer activity. Thus, the introduction of phenyl substituents increases the likelihood of investigated pyrazolo[1,5-a][1,3,5]triazines interacting with protein molecules (Biomolecule) by the π stacking mechanism. In both methyl and phenyl derivatives of pyrazolo[1,5-a][1,3,5]triazines, the second electronic transition includes the n-MO (the level of the lone electron pair in two-coordinated nitrogen atoms). The highest intensity of the η→π* electronic transition is observed in pyrazolo[1,5-a][1,3,5]triazine with pyridine residue, which does not exhibit anti-cancer activity, but exhibits antiviral activity [13]. It can be assumed that the possibility of the formation of [Pharmacophore-Biomolecule] complex by hydrogen bonding ([H-B]) mechanism with protein molecules increases.

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