Organic Chemistry 9th Edition

Published by Brooks Cole
ISBN 10: 1305080483
ISBN 13: 978-1-30508-048-5

Chapter 2 - Polar Covalent Bonds; Acids and Bases - Problem: 12

Answer

Phenylalanine is a stronger acid than Tryptophan.

Work Step by Step

An acid with a small $pK_{a}$ value or a large $K_{a}$ value is a strong acid. A weaker acid, in comparison, has a smaller $K_{a}$ value or a larger $pK_{a}$ value. $pK_{a}$ of Phenylalanine = 1.83 $pK_{a}$ of Tryptophan = 2.83 smaller value of $pK_{a}$ = 1.83 (for Phenylalanine) and hence it is stronger of the two.
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