# Unequal bond lengths of resonating bonds in dinitrogen trioxide

Here is an image showing the resonance structures of $$\ce{N2O3}$$ molecule,

As the bonds numbered (2) and (3) are in resonance, they will have same bond lengths but each with bond order less than two. As the bond numbered (1) doesn't involve in resonance, it will have a bond order of two. Hence, the order of $$\ce{N-O}$$ bond lengths is (1)>(2)=(3).

But according to Wikipedia, all the three $$\ce{N-O}$$ bond lengths are of different lengths! Here is an image form Wikipedia showing the bond lengths and the bond angles in $$\ce{N2O3}$$, So my question is why are the resonating bonds are of different lengths?

• Bonds don't "resonate", and in dissymmetric molecule won't be equal Commented Aug 27, 2022 at 15:44
• Consider the relative energies of the two resonance structures Commented Aug 27, 2022 at 16:48
• Could you explain what you mean by and why you think "As the bonds numbered (2) and (3) are in resonance, they will have same bond lengths"? Commented Aug 27, 2022 at 19:38
• @Mithoron if the bonds aren't in resonance, then there could be a significant difference in the bond lengths of bonds (2) and (3). Commented Aug 28, 2022 at 0:49
• @Andrew I understand what you are saying. So according to bond lengths data, second resonating structure is more contributing than the first one. Can you explain, why? Commented Aug 28, 2022 at 0:51

The two oxygen atoms on the $$\ce{NO2}$$ nitrogen are not equivalent. The molecule is planar*, and one $$\ce{NO2}$$ oxygen (call it the "cis" oxygen) is closer to the third oxygen atom than the other $$\ce{NO2}$$ oxygen ("trans").