Question 21.3: Ionic Forms of Amino Acids Explain in simple terms why an am...
Ionic Forms of Amino Acids
Explain in simple terms why an amino acid is never found in this form:
Strategy
To understand the form of amino acids, we have to understand the acidic and basic nature of the functional groups, whether in qualitative or quantitative terms. We know from previous chapters that carboxyl groups are weak acids and amino groups are weak bases, at least compared to water. So, an amino acid is composed of at least one weak acid and one weak base in the same molecule.
An amino acid is never found in any significant amount in the form shown above because the COOH is a stronger acid than water, and the amino group is a stronger base than water. The carboxyl has a hydrogen to donate, and the amino group can accept a hydrogen. In very un-scientific terms, the hydrogen is not going to be found on the stronger acid and removed from the stronger base. That is why the zwitterion predominates.