What is the Difference Between Zwitterion and Dipole

The key difference between zwitterion and dipole is that zwitterion is a neutral molecule having inner electric charges, whereas dipole is the presence of positive and negative charged ends or north and south magnetic poles.

The terms zwitterion and dipole are related to each other according to the presence of two opposite phenomena in the same system. For example, zwitterions contain positive and negative charges in the same molecule, while electric dipole contains positive and negative charged ends on the same electric field.

CONTENTS

1. Overview and Key Difference
2. What is Zwitterion  
3. What is Dipole
4. Zwitterion vs Dipole in Tabular Form
5. Summary – Zwitterion vs Dipole 

What is Zwitterion?

Zwitterion, or the inner salt, is a molecule consisting of an equal number of positive and negative charged functional groups. In other words, a zwitterion contains both cationic and anionic groups in the same molecule in equal amounts. The term zwitterion mainly comes along with amino acids, but it is also used with sulfamic acid molecules, anthranilic acid, and EDTA protonation.

For example, amino acids in an aqueous solution form a chemical equilibrium between the parent amino acid molecule and the zwitterion. This chemical equilibrium forms through two steps. At the first step, a proton is transformed from the carboxyl group of the amino acid molecule to a water molecule, forming hydronium ion and the negatively charged chemical species of amino acid. Thereafter, in the second step, a proton is transferred from the hydronium ion to the amine group of the same amino acid molecule, now having a negative charge. This forms a positive charge on the amine group while there is a negative charge on the carboxyl group. Therefore, an isomerization reaction takes place, forming a zwitterion.

Generally, it is not possible to study the equilibrium between the compound and its zwitterion experimentally. However, we can gain some insights using the theoretical background.

What is Dipole?

The term dipole refers to the electric or magnetic dipole that is used in electromagnetism. Electric dipoles deal with the separation of opposite charges (positive and negative charges) in any electromagnetic system. E.g. a pair of electric charges having equal magnitude and opposite charge signs and are separated by a small distance. In a magnetic dipole, we can observe a closed circulation of an electric current system.

Whether it is an electric dipole or a magnetic dipole, we can characterize them by dipole moment. Dipole moment is a vector quantity. In a simple electric dipole, the dipole moment directs from the negative charge towards the positive charge. The magnitude of this dipole moment is equal to the strength of each of these charges, times the separation distance between these charges. Similarly, there is a magnetic dipole moment for magnetic dipoles which points through the magnetic current loop. It has a magnitude that is equal to the current in the loop times the area of the loop.

Moreover, there can be some other classifications for dipoles; for example, there is a physical dipole that contains two equal and opposite point charges; point dipole is the limit that we can obtain by letting the separation become zero while keeping a fixed dipole moment, etc.

What is the Difference Between Zwitterion and Dipole?

The terms zwitterion and dipole are related to each other according to the presence of two opposite phenomena in the same system. However, the key difference between zwitterion and dipole is that zwitterion is a neutral molecule having inner electric charges, whereas dipole is the presence of positive and negative charged ends or north and south magnetic poles.

The following table presents the difference between zwitterion and dipole in detail.

Summary – Zwitterion vs Dipole

The terms zwitterion and dipole are related to each other based on the presence of two opposite phenomena in the same system. The key difference between zwitterion and dipole is that zwitterion is a neutral molecule having inner electric charges whereas dipole is the presence of positive and negative charged ends or north and south magnetic poles.

Reference:

1. Helmenstine, Anne Marie. “Dipole Definition in Chemistry and Physics.” ThoughtCo, Aug. 29, 2020.

Image Courtesy:

1. “Amino Acid Zwitterion Structural Formulae V.1” By Jü – Own work (CC0) via Commons Wikimedia
2. “DipoleContourPoint” By Geek3 – Own work (CC BY-SA 4.0) via Commons Wikimedia