# Lewis Acid or Lewis Base?

1. Mar 7, 2010

### crm07149

1. The problem statement, all variables and given/known data
Is H3CC(=O)CH2CH3 more likely to act as a Lewis Acid or Lewis Base? Explain your choice.

Same for HCO2H (formic acid)

2. Relevant equations
N/A

3. 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.

2. Feb 6, 2017

### TeethWhitener

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

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.