Nitrogen oxide three-electron bond

One-electron oxidation of l,6-diazabicyclo[4.4.4]tetradecane proceeds at a remarkably low rate. The cation-radical obtained contains a three-electron o bond between the two nitrogen atoms (Alder and Sessions 1979). In this case, the three-electron bond links the two nitrogens that are disjoined in the initial neutral molecule, at the expense of one electron from the lone electron pair of the first nitrogen and the two electrons of the second nitrogen, which lasts as if it is unchangeable. The authors named such a phenomenon as strong inward pyramidalization of the nitrogens with remarkable flexibility for the N—N interaction. This interaction results in 2a-la bond formation (Scheme 3.21). 

Related three-electron bond radical-cations 1 are formed from dialkyl sulphides by oxidation with hydroxyl radicals generated using pulse radiolysis [2]. An isoe-lectronic three-electron bond between two nitrogen atoms in 2 is formed by reduc-... 

Let us now consider the formation of three-electron bonds between different atoms. Stabilization of an oxidized sulfur atom can, in principle, be achieved in cases of its interaction with other heteroatoms if they provide free (preferably p-) electron pairs. Nitrogen, oxygen, and halogens (except fluorine) can be mentioned as such heteroatoms (Anklam et al. 1988 Carmichael 1997). The stability of these bonds is generally not as high as that of a symmetric S.. S system. An important reference for the enhanced stability of symmetrical three-electron bonds is Clark s (1988) calculations. 

The structure with the three electron bond between nitrogen and oxygen is the best description of the bonding situation in nitric oxide. 

Nanosecond laser flash photolysis has been used to generate sulfur radical cations of S-methylglutathione, via one-electron oxidation by triplet 4-carbo ybenzophenone. Sulfur-o ygen and sulphur-nitrogen three electron bonded species have been identified where the o)ygen and nitrogen atoms are in the peptide bonds. 

C-Nitroso compounds, oximes, N-hydroxyguanidines and N-hydroxyureas each contain an N-O bond and release nitric oxide (NO) or one of its redox forms under some conditions. The nitrogen atom of a C-nitroso compound formally exists in the +1 oxidation state, the same oxidation state as nitroxyl (HNO), the one-electron reduced form of N O. The nitrogen atoms of oximes, N-hydroxyguanidines, and N-hydroxyureas each formally exist in the -1 oxidation state, the same oxidation state as hydroxylamine. Consequently, the direct formation of NO (formal oxidation state = +2) from any of these species requires oxidation, one electron for a C-nitroso compound and three electrons for an oxime, N-hydroxyguanidine or N-hydroxyurea. This chapter summarizes the syntheses and properties, NO-releasing mechanisms and the known structure-activity relationships of these compounds. 

Secondly, a triply bonded dinitrogen molecule, in which each nitrogen has an oxidation of zero, bonds to the atomic nitrogen anion to give rise to one of the canonical structures of the azide anion, namely, one terminal nitrogen has one lone pair and three homoatomic bonds, and so has an oxidation number of zero. The central atom has four homoatomic bonds, but one of which is polarised away from it, i.e. the dative bond, and so it has an oxidation number of+1. The other terminal nitrogen started with one extra electron and now also has a homoatomic bond, which is polarised towards it, and so now has an oxidation number of-2. This nitrogen atom has three lone pairs. 

In common with other first-row elements, nitrogen has only four orbitals available for bond formation, and a maximum of four 2c-2e bonds may be formed. However, since formation of three electron-pair bonds completes the octet, N( R)3, and the nitrogen atom then possesses a lone pair of electrons, four 2c-2e bonds can only be formed either (a) by coordination, as in donor-acceptor complexes, e.g., F3B—N(CH3)3, or in amine oxides, e.g. (CH3)3N—6, or (b) by loss of an electron, as in ammonium ions NH, NR 4. This loss of an electron gives a valence-state configuration for nitrogen (as N+) with four unpaired electrons in sp3 hybrid orbitals analogous to that of neutral carbon, while, as noted above, gain of an electron (as in... 

Such a formulation allows the nitrogen to be bonded to the three oxygen atoms by using its 2s and 2p electrons, but shows the difficulty that arises with both valency and oxidation state concepts. The formula allows the nitrogen atom to exhibit its expected valency of three in that it participates in three electron pair bonds, not counting the coordinate bond as such. The oxidation state of the nitrogen atom is +5 if the oxygen atoms are counted as -2 N + 30 -. 

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