CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Nitric acid, HNO3, can be represented by resonance structures in which one N–O bond is formally a single bond to the hydroxyl oxygen, and the other two N=O bonds are formally double bonds to terminal oxygens. Experimental data show that all three N–O bond lengths are nearly equal and intermediate between typical single and double N–O bonds.
Investigate the bonding and orbital interactions responsible for this observation.
(1) Determine the hybridization of the nitrogen atom and of each oxygen atom in a single resonance structure of HNO3. (Assume the hydroxyl oxygen is bonded through a single σ bond to nitrogen, and the two terminal oxygens are bonded through σ and π interactions.)
(2) For the N–O bond that is single in the chosen resonance structure, specify the two orbitals that overlap to form its σ bond.
(3) For one N=O bond that is double in the chosen resonance structure, identify (i) the orbitals that overlap to form its σ bond and (ii) the orbitals that overlap to form its π bond.
(4) Explain how the delocalization of π electrons across the three N–O bonds leads to bond orders that are all greater than 1 but less than 2.
(5) Based on your explanation, predict and justify the relative lengths of the three N–O bonds compared with a typical N–O single bond and a typical N=O double bond.