CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Formate ion, HCO2−, is the conjugate base of formic acid and is often used as a ligand in coordination chemistry.
(a) Draw all resonance structures for HCO2− that satisfy the octet rule and include all non-bonding electrons.
(b) Calculate the formal charge on each atom for every structure from part (a). Identify which resonance forms make the greatest contributions to the resonance hybrid, and justify your choice.
(c) Experimental data show that the two C–O bonds in HCO2− are the same length. Use your resonance analysis to explain this observation.
(d) Formic acid (HCO2H) has a pKa of 3.75, whereas methanol (CH3OH) has a pKa of 15.5. Use resonance stabilization of the conjugate base to account for the difference in acidity between the two acids.