Delocalization of Lone-Pair Electrons into Antibonding Orbitals: Increased-Valence Structures, Molecular Orbital Theory and Atomic Valencies

This paper aims at giving a general survey of the part played by lone-pair electrons in the range of phenomena commonly classified under the heading of molecular association, with particular emphasis on the liquid state. The position of lone-pair electrons on a molecule and the factors determining their availability for forming intermolecular links are discussed in terms of molecular orbital theory. This is followed by an examination of the way in which these association forces influence the structure of large aggregates of molecules as in liquids. The lines along which a quantitative theory of associated liquids may be developed are indicated.

Download Full-text

Delocalization of a Lone-Pair Electron into a Vacant Antibonding Orbital: Increased-Valence Structures, Molecular Orbital Theory and Atomic Valencies

Lecture Notes in Chemistry - Bonding in Electron-Rich Molecules ◽

10.1007/978-3-319-16676-6_14 ◽

2015 ◽

pp. 191-203

Author(s):

Richard D. Harcourt

Keyword(s):

Molecular Orbital ◽

Lone Pair ◽

Molecular Orbital Theory ◽

Antibonding Orbital ◽

Orbital Theory ◽

Lone Pair Electron ◽

Increased Valence

Download Full-text

The Electronic Structures of A2Y4 Molecules

Australian Journal of Chemistry ◽

10.1071/ch9630737 ◽

1963 ◽

Vol 16 (5) ◽

pp. 737 ◽

Cited By ~ 39

Author(s):

RD Brown ◽

RD Harcourt

Keyword(s):

Molecular Orbital ◽

Electronic Structures ◽

Lone Pair ◽

Orbital Method ◽

Molecular Orbital Theory ◽

Bond Properties ◽

Orbital Theory ◽

The Core ◽

Valence Electrons ◽

Charge Rule

A study of the electronic structures of A2Y4 molecules containing 34, 36, and 38 valence electrons has been made. An approximate VESCF, molecular- orbital method was used, attention being concentrated mainly on the delocalization of σ-electrons which are classically regarded as lone-pairs on the Y atoms. The results provide explanations of the main features of many of the observed AA- and AY-bond lengths and YAY-bond angles of N2O4, C2O42-, B2F4, B2Cl4, C2F4, C2Cl4, S2O42-, and N2F4. Other A2Y4 systems which have either not been fully characterized or not yet reported are also considered. The extent of lone-pair delocalization is shown to be governed by a parameter aσ, related to the coulomb and resonance parameters of H�ckel molecular-orbital theory. General trends in the value of aσ can be predicted from values of the core charges of A and Y towards the o-electrons concerned. A more detailed "adjacent charge" rule emerges. It differs from the classical rule in that for A2Y4 systems, adjacent negative formal charges on the A atoms should not very greatly affect the AA-bond properties. Difficulties were encountered in consistently interpreting the properties of some A2F4 and A2Cl4 compounds. These deserve further attention.

Download Full-text