This question has already been asked link Why doesn't nitrogen monoxide dimerize?

but explination is not clear. I would like it to be explained in simple manner using molecular orbital diagram is included please explain in simple term using molecular orbital theory.

Why this is not the case

In NO2, when drawing it's Lewis structure, you'll see that valency of nitrogen isn't satisfied, there is and odd electron left on it making it somewhat unstable.

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Odd electron get fulfilled when it dimerises.

enter image description here

  • $\begingroup$ If you think the answers to the question aren't sufficient, try gaining some rep and offering a bounty. $\endgroup$ – ringo Dec 9 '18 at 0:53
  • $\begingroup$ I have already put a link saying that its already been asked $\endgroup$ – Chemist Dec 9 '18 at 1:18

Nitric oxide (nitrogen monoxide) has one more electron than the N2 molecule. N2 has a sigma framework (sp hybridized) with 2 electrons in the outward lone pair on each nitrogen and one electron from each nitrogen in the sigma bond. The remaining 2 electrons on each nitrogen are in the two pi bonds, so that each nitrogen has a total of 8 electrons: 2 in the lone pair, 2 in the sigma bond and 4 in the two pi bonds. N2 has a bond order of 3.

The extra electron in NO goes into an antibonding pi molecular orbital. The resulting bond order in NO is 2.5. A high-energy antibonding pi electron is not well designed for bonding to anything, and yet, solid NO has been found to consist of loose dimers with a rectangular structure: the tightly bonded N-O bond is 1.10 Angstroms long and it is bonded N to O and O to N, with a separation of 2.38 A between the monomer NO molecules.

Reference is Advanced Inorganic Chemistry, Cotton and Wilkinson, 1966

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