Valence-bond studies of 4-electron 3-centre bonding units. I. The π-electrons of O3, NO2−, and CH2N2

1978 ◽  
Vol 56 (8) ◽  
pp. 1093-1101 ◽  
Author(s):  
Richard D. Harcourt ◽  
Walter Roso
Keyword(s):  
Electronic Structure ◽  
Ab Initio ◽  
Valence Bond ◽  
Ground States ◽  
Wave Functions ◽  
Dipolar Cycloaddition ◽  
Cycloaddition Reactions ◽  
Electronic Mechanism ◽  
Increased Valence

Some ab-initio valence-bond wave-functions are reported for the π-electrons of the ground-states of O3, NO2−, and CH2N2. Examination of these wave-functions provides further support for the hypothesis that, for the ground-states of many electron-excess molecules, important valence-bond structures are those that are compatible with the electroneutrality principle, i.e. they carry either small or zero formal charges on each of the atoms. For O3 and CH2N2, the important valence-bond structures with zero atomic formal charges are [Formula: see text]Each of these structures has a 'long-bond' between non-adjacent atoms. The significance of 'long-bond' (or spin-paired diradical) structures for the electronic mechanism of 1,3-dipolar cycloaddition reactions is discussed and 'increased-valence' descriptions of the electronic structure of each molecule are presented. Some comments on the utility of 'increased-valence' structures are provided.

Ab initio double-ζ (D95) valence bond calculations for the ground states of NO2, O3, and ClO2

2005 ◽  
Vol 358 (14) ◽  
pp. 4131-4136 ◽  
Author(s):  
Thomas M. Klapötke ◽  
Richard D. Harcourt ◽  
Jiabo Li
Keyword(s):  
Ab Initio ◽  
Valence Bond ◽  
Ground States

Ab initio calculations of the electronic structure of the ground states of HBeHe+ and BeHe22+

2007 ◽  
Vol 442 (4-6) ◽  
pp. 194-200 ◽  
Author(s):  
Alister J. Page ◽  
David J.D. Wilson ◽  
Ellak I. von Nagy-Felsobuki
Keyword(s):  
Electronic Structure ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Ground States

Ab Initio Double-ζ (D95) Valence Bond Calculations for the Ground States of S2N2and S42+

2004 ◽  
Vol 108 (31) ◽  
pp. 6527-6531 ◽  
Author(s):  
Thomas M. Klapötke ◽  
Jiabo Li ◽  
Richard D. Harcourt
Keyword(s):  
Ab Initio ◽  
Valence Bond ◽  
Ground States

Molecular orbital, increased valence, valence bond and non-pairing spatial orbital formulae for three-centre bonding

1969 ◽  
Vol 22 (2) ◽  
pp. 279 ◽  
Author(s):  
RD Harcourt
Keyword(s):  
Molecular Orbital ◽  
Valence Bond ◽  
Wave Functions ◽  
Bond Orders ◽  
Increased Valence

The simple valence-bond and molecular orbital formulae for three-centre bonding involving four electrons and three atoms Y, A, and B are Y 4-B - Y-A 'P, and Y---A---B Increased-valence formulae that have been developed recently are Y-A . B and Y . A-B If Y and B are the same type of atom, and bond-orbitals are used as wave functions for Y-A and A-B bonds, then the near-equivalence of the molecular orbital and increased-valence wave functions is demonstrated. Bond-orders (or numbers) for these and Linnett's5s6 non-pairing spatial orbital formula Y . A . B are calculated.

Ab initio Double-ζ (D95) Valence Bond Calculations for the Ground States of S2N2 and S42+.

ChemInform ◽  
2004 ◽  
Vol 35 (41) ◽  
Author(s):  
Thomas M. Klapoetke ◽  
Jiabo Li ◽  
Richard D. Harcourt
Keyword(s):  
Ab Initio ◽  
Valence Bond ◽  
Ground States

Increased-Valence or Electronic Hypervalence for a Diatomic One-Electron Bond

2005 ◽  
Vol 58 (10) ◽  
pp. 753 ◽  
Author(s):  
Richard D. Harcourt
Keyword(s):  
Excited State ◽  
Molecular Orbital ◽  
Valence Bond ◽  
Ground States ◽  
Bond Valence ◽  
Atomic Orbitals ◽  
Valence Bond Structure ◽  
The One ◽  
Increased Valence

With a and b as overlapping atomic orbitals to form the A–B bonding molecular orbital ψab = a + kb, it is deduced that for k ≠ 0, 1, or ∞, either the A atom or the B atom in the one-electron bond valence bond structure (A · B) exhibits increased-valence or electronic hypervalence, namely its valence exceeds unity. The result is illustrated using the results of STO-6G valence bond calculations for the one-electron bond of LiH+ and an excited state for H2CN. Valencies for the ground-states of H2+, H2, and H2− are also considered.

Some wave functions for the four-electron threecentre bonding of four- and eight-π-electron systems

1974 ◽  
Vol 27 (4) ◽  
pp. 691 ◽  
Author(s):  
RD Harcourt ◽  
JF Sillitoe
Keyword(s):  
Molecular Orbital ◽  
Configuration Interaction ◽  
Electron Pair ◽  
Valence Bond ◽  
Pair Bond ◽  
Wave Functions ◽  
Electron Systems ◽  
Numerical Evidence ◽  
The One ◽  
Increased Valence

For symmetrical four-electron three-centre bonding units, the standard valence-bond (VB), delocalized molecular orbital (MO), increased-valence (IV) and non-paired spatial orbital (NPSO) representations of the electrons are Diagram O3, NO2- and CF2 with four π-electrons, and N3-, CO2 and NO2+ with eight π-electrons, have respectively one and two four-electron three-centre bonding units for these n-electrons. By means of Pople-Parr-Pariser type approximations, the MO, standard VB, IV and NPSO wave functions for these systems are compared with complete VB (or best configuration interaction) wave functions for the ground states. Similar studies are reported for the n-electrons of N2O. Further demonstration is given for the important result obtained elsewhere that the IV formulae must always have energies which are lower than those of the standard VB formulae, provided that the same technique is used to construct electron-pair bond wave functions. The extra stability arises because IV formulae summarize resonance between the standard VB formulae and long-bond formulae of the type Diagram As has been discussed elsewhere, the latter structure can make appreciable contributions to the complete VB resonance when its atomic formal charges are either zero or small in magnitude.If two-centre bond orbitals are used to construct the wave functions for the one-electron bond(s) and the two-electron bond(s) of IV formulae, then the IV and MO wave functions are almost identical for the symmetrical systems. Further numerical evidence is provided for this near-equivalence.

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