15.8B: Nitrogen Monoxide, \(NO\)
- Page ID
- 34234
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Nitrogen Monoxide (Nitric Oxide)
- Nitric oxide is a colourless paramagnetic gas.
- It is made, for example, by the reduction of concentrated nitric acid by copper, or reduction of nitrates and nitrites:
HNO3 + 3Cu 3Cu(NO3)2 + 4H2O + 2NO - Its reaction include:
- Oxidation to NO2 by oxygen or to nitric acid by permanganate (used for its analysis).
- Reduction to N2O (e.g. by sulphur dioxide) or NH2OH (e.g. by Cr2+).
- It disproportionates at high temperature to N2O and NO2.
- It is implicated in blood pressure control.
- An odd-electron molecule, the bond order (which is most clearly rationalized using molecular orbital theory) is 2.5, with the odd electron in a p-antibonding orbital. This electron is easily lost to give the NºO+ ion which is isolectronic with CºO or CºN–. The bond in NO+ is 0.09 Å shorter than in NO, and the stretching vibration frequency increases from 1840 cm-1 to 2150-2400 cm-1 depending on how the NO+ is behaving as a s-donor or p-acceptor ligand.
Note that dimerization to O=N-N=O would not increase the (total) number of bonds, and turns out to be energetically unrewarding.
- Nitrosonium salts include [NO]+2SO42- implicated in the "lead chamber process" for the manufacture of sulphuric acid.