Chapter 6 Pauling “3-Electron Bonds”,
5-Electron 3-Centre Bonding and
Some Tetra-Atomic Radicals
Valence-bond structures with Pauling “3-electron bonds” between pairs of atoms
may be constructed for a number of triatomic radicals. Here we shall examine
these types of structures for some radicals with either 17 or 19 valence-shell electrons. For these systems, it is necessary to involve the participation in resonance of
two Pauling “3-electron bond” structures. The delocalized molecular orbital equivalent of this resonance involves the construction of three 3-centre molecular
orbitals to accommodate five electrons; this is described in Section 6-4.
6-1 NO 2
Nitrogen dioxide with 17 valence-shell electrons is perhaps the most familiar triatomic molecule for which Pauling “3-electron bond” theory is appropriate. Electron spin resonance measurements indicate that the odd electron is delocalized
over the three atomic centres; estimates of the nitrogen and oxygen odd-electron
charges are 0.52 and 0.24 (Table 6-1), respectively.
(For the purpose of qualitative discussion, we shall approximate these oddelectron charges to 0.5 and 0.25.) Each of the N-O bonds of
2
NO has a length
1 of
1.19 Å and the O-N-O bond angle
1 is 134°. These observations suggest that
resonance between the Lewis structures (1)-(4)
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_6
75
5-Electron 3-Centre Bonding and
Some Tetra-Atomic Radicals
Valence-bond structures with Pauling “3-electron bonds” between pairs of atoms
may be constructed for a number of triatomic radicals. Here we shall examine
these types of structures for some radicals with either 17 or 19 valence-shell electrons. For these systems, it is necessary to involve the participation in resonance of
two Pauling “3-electron bond” structures. The delocalized molecular orbital equivalent of this resonance involves the construction of three 3-centre molecular
orbitals to accommodate five electrons; this is described in Section 6-4.
6-1 NO 2
Nitrogen dioxide with 17 valence-shell electrons is perhaps the most familiar triatomic molecule for which Pauling “3-electron bond” theory is appropriate. Electron spin resonance measurements indicate that the odd electron is delocalized
over the three atomic centres; estimates of the nitrogen and oxygen odd-electron
charges are 0.52 and 0.24 (Table 6-1), respectively.
(For the purpose of qualitative discussion, we shall approximate these oddelectron charges to 0.5 and 0.25.) Each of the N-O bonds of
2
NO has a length
1 of
1.19 Å and the O-N-O bond angle
1 is 134°. These observations suggest that
resonance between the Lewis structures (1)-(4)
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_6
75