Chapter 14 Delocalization of a Lone-Pair
Electron into a Vacant Antibonding
Orbital:
Structures, Molecular Orbital
Theory and Atomic Valencies
Three related topics that involve diatomic antibonding orbitals will be discussed in
this chapter. First, “increased-valence” structures for 4-electron 3-centre bonding
units will be constructed by delocalizing a lone-pair electron on one atom into an
antibonding orbital between a pair of adjacent atoms. Then the approximate 3centre molecular orbital theory that arises from delocalization of lone-pair
electrons into an antibonding orbital will be presented, with emphasis given to the
relationship that exists between the “increased-valence” and the molecular orbital
theory. Finally, by making particular use of the charge distribution for antibonding
orbitals, expressions for atomic valencies will be deduced for “increased-valence”
structures.
14-1 Delocalization of a Lone-Pair Electron into a Vacant
Antibonding Orbital
The third method for generating “increased-valence” structures utilizes the molecular orbital description of the Pauling “3-electron bond” in terms of bonding and
antibonding orbitals.
We shall commence our discussion by recalling that “increased-valence”
structure (1) involves the electron spin distributions of structures (2) and (3).
Ó Springer International Publishing Switzerland 2016
R.D. Harcourt, Bonding in Electron-Rich Molecules,
Lecture Notes in Chemistry 90, DOI 10.1007/978-3-319-16676-6_14
191
“Increased-Valence”
Electron into a Vacant Antibonding
Orbital:
Structures, Molecular Orbital
Theory and Atomic Valencies
Three related topics that involve diatomic antibonding orbitals will be discussed in
this chapter. First, “increased-valence” structures for 4-electron 3-centre bonding
units will be constructed by delocalizing a lone-pair electron on one atom into an
antibonding orbital between a pair of adjacent atoms. Then the approximate 3centre molecular orbital theory that arises from delocalization of lone-pair
electrons into an antibonding orbital will be presented, with emphasis given to the
relationship that exists between the “increased-valence” and the molecular orbital
theory. Finally, by making particular use of the charge distribution for antibonding
orbitals, expressions for atomic valencies will be deduced for “increased-valence”
structures.
14-1 Delocalization of a Lone-Pair Electron into a Vacant
Antibonding Orbital
The third method for generating “increased-valence” structures utilizes the molecular orbital description of the Pauling “3-electron bond” in terms of bonding and
antibonding orbitals.
We shall commence our discussion by recalling that “increased-valence”
structure (1) involves the electron spin distributions of structures (2) and (3).
Ó Springer International Publishing Switzerland 2016
R.D. Harcourt, Bonding in Electron-Rich Molecules,
Lecture Notes in Chemistry 90, DOI 10.1007/978-3-319-16676-6_14
191
“Increased-Valence”