Question

Each of the compounds, a (ethanimine) and b (acetonitrile), protonates on nitrogen. Draw the conjugate acid of each. Select the strongest acid and the strongest base from the four species.

1) Ethanimine is the conjugate acid of a and acetonitrile is the conjugate acid of b.
2) Acetonitrile is the conjugate acid of a and ethanimine is the conjugate acid of b.
3) Ethanimine is the strongest acid and acetonitrile is the strongest base.
4) Acetonitrile is the strongest acid and ethanimine is the strongest base.

Answer 1

Acetonitrile is the strongest acid and ethanimine is the strongest base.

Ethanamine exhibits more pronounced basic behavior than acetonitrile's acidic characteristics. We must have to look at the structure of the compounds to find why the acetonitrile will be found to be a much stronger acid.

We can see that in the acetonitrile, we do have a triple bond that we know is quite electron withdrawing and as such there is going to be a large pull on the electron density that holds the proton causing it to be easily lost.