Lewis Acid or Lewis Base?

[crm07149]

Homework Statement

Is H3CC(=O)CH2CH3 more likely to act as a Lewis Acid or Lewis Base? Explain your choice.

Same for HCO2H (formic acid)

Homework Equations

N/A

The Attempt at a Solution

Since a Lewis Base donates electron pairs, and the oxygen in H3CC(=O)CH2CH3 has two lone pairs, I reasoned that H3CC(=O)CH2CH3 is a Lewis Base.

I know HCO2H should be a Lewis Acid because it is formic acid, but I don't know how the molecule would accept an electron pair.

 

[TeethWhitener]

I know HCO2H should be a Lewis Acid because it is formic acid, but I don't know how the molecule would accept an electron pair.

The acidic proton accepts an electron pair. This is usually followed by the proton leaving to attach to the electron pair donor.

Since a Lewis Base donates electron pairs, and the oxygen in H3CC(=O)CH2CH3 has two lone pairs, I reasoned that H3CC(=O)CH2CH3 is a Lewis Base.

This answer is fine, though I will point out that methyl ethyl ketone can also display weak acidity through keto-enol tautomerization. Essentially, the proton on the hydroxyl group in the enol form of this molecule is slightly acidic. So this molecule can actually be either a Lewis acid or a Lewis base.