Valence Bond Studies of N2F+

2003 ◽  
Vol 56 (11) ◽  
pp. 1121 ◽  
Author(s):  
Richard D. Harcourt
Keyword(s):  
Bond Length ◽  
Positive Charge ◽  
Valence Bond ◽  
Vb Structures ◽  
Single Positive

The results of STO-6G valence bond (VB) calculations for the linear cation N2F+ show that (a) the dominant Lewis-type VB structures involve a single positive charge which is located on either of the nitrogen atoms, and (b) a small amount of N–F π-bonding arises primarily from the formation of one-electron N–F π-bonds. It is suggested that N–F π-bonding is one of several factors which are responsible for the shortening of the N–F bond of N2F+ relative to that of NF4+. Valence bond and bond length considerations imply that the extent of N–O π-bonding in N2O and NO43- exceeds the degree of N–F π-bonding in N2F+ and NF4+.

The valence-bond theory of molecular structure II. Reformulation of the theory

1954 ◽  
Vol 223 (1154) ◽  
pp. 306-323 ◽  
Keyword(s):  
Valence Bond ◽  
Closed Shell ◽  
Numerical Illustration ◽  
Atomic Orbitals ◽  
Spin Eigenfunctions ◽  
Spin Pairing ◽  
Vb Structures ◽  
Bond Theory ◽  
Strong Repulsion ◽  
A Charge

The construction of spin eigenfunctions and the evaluation of matrix elements between ,them are discussed generally in preparation for a development of the valence bond (VB) theory along the lines indicated in I. The customary approximation of considering explicitly only the electrons outside a ‘closed shell’ is shown to be defensible. The reformulation of the VB theory is now straightforward, but its final description of bonding is quite new. Atomic orbitals (AO’s) are replaced, whenever they appear, by orthogonalized atomic orbitals (AO’s); but when the assumptions of the conventional theory are rigorously validated in this way the ‘covalent’ structures (now ‘VB’ structures) are found, quite generally, to indicate only strong repulsion between the ‘bonded’ atoms, and formal descriptions of bonding and of bond orders, in terms of ‘spin-pairing’, become nonsensical. Bonding can be described only by admitting into the wave functions polar VB structures; a bond between two atoms demands the appearance (with considerable weight) of pairs of structures differing by a ‘charge hop’ between the atoms concerned. The conventional VB structures are found to be equivalent to certain groupings of VB structures (non-polar and polar) and do, indeed, predict bonds between spin-paired atoms and repulsion between the atoms of different pairs. It is then possible to make full use of chemical intuition, using a plausible combination of conventional structures as a starting approximation in the more rigorous theory. A numerical illustration is provided by a discussion of the Kekulé structures of benzene. Some important characteristics of energy calculations in the VB theory are pointed out. Quantities of intra - and inter -atomic origin are well separated, and the method is apparently well suited to development along either ab initio or empirical lines.

Bimodal Effect of Amphiphilic Biocide Concentrations on Fluidity of Lipid Membranes

1996 ◽  
Vol 51 (11-12) ◽  
pp. 853-858 ◽  
Author(s):  
Marian Podolak ◽  
Dariusz Man ◽  
Stanislaw Waga ◽  
Stanislaw Przestalski
Keyword(s):  
Binding Energy ◽  
Lipid Membranes ◽  
Positive Charge ◽  
Egg Yolk ◽  
Biologically Active ◽  
Double Positive ◽  
Dipole System ◽  
Monovalent Ions ◽  
Single Positive ◽  
High Concentrations

Abstract Using the spin label method (ESR) it has been shown that biologically active, amphiphilic compounds (quaternary ammonium salts -AS) containing polar heads with single and double positive charge caused, at low concentrations, decrease fluidity of liposome membranes formed with egg yolk lecithin (EYL). At higher concentrations an increase in fluidity was observed. With compounds having a single positive charge minimum fluidity of membrane structure occurs in the range of 1 to 3%, with compounds containing double positive charge -in the range of 4 -6 % . That effect does not depend on polar head size and length of alkyl chains of the AS used. Analysis of the electrostatic interaction between positive charges and dipole system suggest that at low ion concentrations the binding energy of the system increases, while it decreases at high concentrations. For the model presented, maxi­mum of binding energy of the system occurs at 3% of positive monovalent ions and at 6% of positive divalent ions admixed.

A simplified empirical model for approximation of the `bond valence–bond length' correlation for H—O bonds

2011 ◽  
Vol 67 (3) ◽  
pp. 263-265 ◽  
Author(s):  
Vasyl Sidey
Keyword(s):  
Bond Length ◽  
Empirical Model ◽  
Valence Bond ◽  
Bond Valence

The `bond valence (s)–bond length (r)' correlation reported earlier for H—O bonds [Brown (2009). Chem. Rev. 109, 6858–6919] has been closely approximated using the function s = (α − βr)1/γ, where α = 1.185 (10), β = 0.321 (8) and γ = 0.36.

The aromatic character and resonance stabilization energies of substituted cyclopentadienyl and indenyl cations

2005 ◽  
Vol 83 (9) ◽  
pp. 1287-1298 ◽  
Author(s):  
J A Pincock ◽  
A WH Speed
Keyword(s):  
Triplet State ◽  
Bond Length ◽  
Positive Charge ◽  
Singlet State ◽  
Substituent Effects ◽  
Bond Alternation ◽  
Carbon Carbon Bond ◽  
Resonance Stabilization ◽  
Stabilization Energies ◽  
Electron Donating Groups

Calculations (B3LYP/6-31G(d)) have been used to assess the aromaticity of 5-X substituted indenyl (4) and cyclopentadienyl (5) cations with X = O–, NH2, OCH3, CH3, F, H, CN, and N2+. Two criteria were used, the aromatic stabilization energy (ASE), as determined by isodesmic reactions, and bond alternation, as determined from the Julg index (A) on the basis of carbon–carbon bond lengths. Substituent effects on the singlet state of the cyclopentadienyl cations resulted in significant decreases in antiaromatic character for electron-donating groups as indicated by larger A values (A = –0.25 for X = H and +0.26 for X = NH2). These decreases paralleled increases in the C-2—C-3 bond length and good linear correlations were obtained between A vs. the C-2—C-3 bond length and A vs. the ASE. These effects were rationalized by the stabilization by the electron-donating groups of the positive charge at C-5 generated as a consequence of a Jahn–Teller distortion leading to a lowest energy singlet state with a HOMO of a2 symmetry. In contrast, the lowest energy triplet state for each of the substituted cyclopentadienyl cations has little bond alternation (A > 0.9) and, by this criterion, is not significantly antiaromatic. The triplet state is more stable than the singlet state for the unsubstituted case and those with electron-withdrawing groups (ΔEST = –11.3 and –9.3 kcal/mol for X = H and CN, respectively) (1 cal = 4.184 J), but less stable for electron-donating groups (ΔEST = +15.0 kcal/mol for X = NH2). For the indenyl cations 4, the ASE values were almost independent of the substituent and the A values only decreased slightly for electron-donating groups. The A values also indicated that the indenyl cations could be divided into two moieties, an X-substituted pentadienyl cation with considerable delocalization and little bond alternation, and a 2,3-butadiene one with considerable bond alternation. This separation also placed the major portion of the positive charge on the pentadienyl part. The lack of symmetry in the substituted indenyl cations rationalizes the selective reactivity of the 5-methoxy-substituted cation at C-1. Finally, the resonance stabilization energies (RSE) of the substituted cations gave a linear correlation with the RSEs of 4-substituted benzylic cations.Key words: indenyl cations, cyclopentadienyl cations, substituent effects, stabilization energies.

An analysis of bond length information for oxygen atoms adsorbed on well-defined metal surfaces

1985 ◽  
Vol 63 (12) ◽  
pp. 3631-3633
Author(s):  
K. A. R. Mitchell ◽  
Susan A. Schlatter
Keyword(s):  
Solid State ◽  
Bond Length ◽  
Nearest Neighbor ◽  
Valence Bond ◽  
Face Centered Cubic ◽  
Interatomic Distances ◽  
Cubic Metals ◽  
New Information ◽  
Face Centered ◽  
Solid State Structures

New bond valence – bond length relations deduced by Brown and Altermatt for solid state structures have been used for rationalizing O—M interatomic distances, measured by various surface crystallographic techniques, for O atoms chemisorbed on well-defined metal (M) surfaces. The advantages of this approach, over the Pauling–Schomaker–Stevenson approach used previously, are especially apparent for initial rationalizations of new information on the nearest-neighbor and next-nearest–neighbor bond lengths for O adsorbed on long-bridge sites of (110) surfaces of face-centered cubic metals.

scholarly journals Antimony lone electronic pair as a stereoelectronic barrier to stibatrane

2021 ◽  
Vol 11 (2) ◽  
pp. 178-186
Author(s):  
V. P. Baryshok ◽  
E. A. Zel'bst
Keyword(s):  
Crystal Structure ◽  
Oxygen Atom ◽  
Bond Length ◽  
Intermolecular Hydrogen Bond ◽  
Valence Bond ◽  
Covalent Bond ◽  
Sodium Methylate ◽  
Antimony Atom ◽  
Nucleophilic Attack ◽  
Coordinate Bond

To examine the effect of 5s2 lone electron pair of antimony atom on the reaction of antimony trifluoride and triethanolamine in the presence of sodium methylate, the crystal structure of the reaction product -2-fluoro-6-(2-hydroxyethyl)-1,3-dioxa-6-aza-2-stibacy-cylooctane (1-fluoro-2-hydrostibatrane) FSb (OCH2CH2)2NCH2CH2OH) was confirmed. In the compound structure, the hydrogen atom of the 2-hydtoxyethyl group of each molecule forms an intermolecular hydrogen bond with the oxygen atom of one of the five-membered SbOCH2CH2N half-cycles in a neighbouring molecule. A geometry of both five-member N-C-C-O-Sb heterocycles, end-capped by transannular N→Sb bond in the 1-fluoro-2-hydrostibatrane molecule, is almost identical. C-O, C-C, N-C interatomic distances and valence angles in two endocyclic units (NCCOSb) are comparable to those observed in RSi(OCH2CH2)3N silatranes. A coordination polyhedron of the Sb atom can be represented as a transition from a bisphenoid to Sb(O3)N trigonal pyramid, with a nitrogen atom at the apex and three oxygen atoms in the base. The N→Sb transannular coordinate bond length is 2.402(4) Å, which is 0.40 Å greater than the Sb-N covalent bond standard length. The Sb-F bond (1.997(4) Å) is 0.12 Å longer than that in the SbF3 molecule, and insignificantly shorter than that of the Sb-Fax (2.028(3) Å) in the SbF3Gly crystalline complex. The fluorine atom substantially strays from the N→Sb axis to the direction of O(1) and O(2) atoms. The oxygen atom of the 2-hydroxyethyl group lies at a distance of 2.899(3) A from that of Sb, intermediate between the valence bond length and the sum of the Van der Waals radii of these atoms. Combined with the F atom position, one can assume the 1-fluoro-2-hydrostibatrane crystal structure as a “frozen” state of the SNi(Sb) type nucleophilic attack of the oxygen atom, uncompleted because of its repulsion by the 5s2 lone electronic pair of antimony atom.

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