# Hyper conjugation in acetic acid?

While comparing the relative stabilities of acetic acid and formic acid why don't we consider the 3 possible hyper conjugative structures which would stabilize the positive charge on carbon thus making the conjugate of acetic acid more stable.

My professor told me hyper conjugation does not operate here. But what is the reason behind this?

• Why do you think the carbon has a positive charge on it ? – Rajesh Mar 25 '15 at 14:20
• Do you mean "making the conjugate base of acetic acid more stable"? – jerepierre Mar 25 '15 at 14:42
• #rajesh. draw the resonating structures and observe it – yasir Mar 25 '15 at 22:31

Hyperconjugation does play a role in your example. Acetic acid ($\mathrm{p}K_\mathrm{a}=4.75$) is a weaker acid than formic acid ($\mathrm{p}K_\mathrm{a}=3.75$). To understand this we must consider the relative stabilities of both the ionized and unionized acids.