I came across this question. According to me, $\ce{NO}$ should have a shorter bond length as it has a triple bond, while $\ce{NOCl}$ has a double bond. But the answer is given that $\ce{NO}$ has greater bond length than $\ce{NOCl}$. Why? Is the answer wrong

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    $\begingroup$ Given the data on Wikipedia NO 115 pm, NOCl 114 pm, there is hardly a difference (I did not cross-validate these values, but I'd say they are essentially the same). Could you please point to the source of this question. $\endgroup$ – Martin - マーチン Apr 8 '19 at 11:43
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    $\begingroup$ The data I found is 115.08+/-0.005 for NO (Herzberg, Diatomic) and 114+/- 2 for NOCl (Cotton & Wilkinson, Inorg Chem) and from this data it is uncertain which NO bond length is greater. $\endgroup$ – porphyrin Apr 8 '19 at 12:16
  • $\begingroup$ I think that $\ce{NO}$ bond order is 2.5 and $\ce{NOCl}$ exist as $\ce{NO+}$ and $\ce{Cl-}$ and $\ce{NO+}$ has bond order 3 that is why $\ce{N-O}$ bond length in $\ce{NOCl}$ is shorter. $\endgroup$ – immortalhero gamer Aug 27 '20 at 3:33

Also relevant: the nitrogen-chlorine bond lengths:

$\ce{NOCl}=196\text{ pm}$ Wikipedia

$\ce{NCl3}=176\text{ pm}$ Wikipedia

The oxygen in nitrosyl chloride is donating its lone pair to the antibonding orbital in the nitrogen-chlorine linkage, weakening that bond but adding more pi bonding between nitrogen and oxygen to become like a triple bond.

If we were supposed to compare bond lengths using "simple" principles of bonding, this is a poor choice. Nitrosyl chloride presents more than meets the eye.

  • $\begingroup$ Interesting take, but I believe it distracts from the general stupidity of the original question, i.e. determining the difference of things that are essentially the same. $\endgroup$ – Martin - マーチン Sep 3 '19 at 12:30
  • $\begingroup$ And the "extra" bonding in nitrosyl chloride explains why they are basically the same. Again, the question does not work for understanding simple bonding principles due to the complexity of nitrosyl chloride. $\endgroup$ – Oscar Lanzi Sep 3 '19 at 13:08

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