Chapter 21, Problem 6A

Interpretation Introduction

Interpretation:

Formulas of two amino acids with polar side chain and two amino acids with non-polar side chain must be written. The reason for the respective polarities of the side chains needs to be explained.

Concept Introduction:

α-Amino acids are a class of compounds which contains at least one carboxylic acid group and at least one amino group at α-carbon (carbon next to COOH). The side chain contains different groups including hydrogen for glycine.

Explanation of Solution

The general amino acid structure is as follows:

  

Two amino acids with polar side chain are aspartic acid (R=CH₂COOH) and serine (R=CH₂OH). Two amino acids with non-polar side chain are valine (R=-CHMe₂) and alanine (R=CH₃).

As shown in the structure aspartic acid and serine have polar side chains which are CH₂COOH and CH₂OH. These are considered as polar side chain as O is more electronegative than both carbon and hydrogen.

Valine and alanine have non-polar side chains which are CHMe₂and CH₃. These are considered as non-polar side chains as electronegativity difference between C and H is very less.