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Meso compounds

Meso compounds, a unique class of molecules in organic chemistry, possess distinct properties that set them apart.

Meso compounds have a plane of symmetry, so they don’t have optical activity even though they have stereocenters. It’s important for researchers and students to know about meso compounds because they’re important in studying molecular structures and reactions.

By examining the whole molecule and its substituents, one can identify the presence of a mirror plane within meso compounds.

Definition and Explanation of Meso Compounds

Meso compounds are unique molecules that have multiple chiral centers but lack overall chirality. This means that even though they possess asymmetry in their structure, they do not exhibit optical activity.

Multiple Chiral Centers with No Overall Chirality

Unlike other chiral compounds that exist as enantiomers (mirror images) and rotate plane-polarized light in opposite directions, meso compounds have an unusual characteristic.

They contain two or more chiral centers within their structure, yet they remain achiral due to the presence of an internal plane of symmetry.

Internal Plane of Symmetry

The internal plane of symmetry divides the molecule into two identical halves. This plane can be imagined as a mirror placed between the chiral centers, reflecting one half onto the other.

As a result, any optical activities generated by one half are canceled out by the opposite activities from the other half.

Canceling Out Optical Activities

This cancellation occurs because the equal and opposite rotations induced by each half of the molecule neutralize each other.

As a result, meso compounds do not exhibit any net rotation of plane-polarized light when dissolved in a solution.

Examples of Meso Compounds

Meso compounds are unique molecules that possess internal symmetry, resulting in their lack of optical activity. Let’s explore some examples to understand these fascinating compounds better.

Tartaric Acid

One well-known example of a meso compound is tartaric acid. This compound contains four carbon atoms and has two chiral centers.

However, despite having chiral centers, tartaric acid does not exhibit optical activity due to its internal symmetry.

Meso-Tartaric Acid

Another intriguing example is meso-tartaric acid. Similar to regular tartaric acid, it also possesses two chiral centers but lacks optical activity because of its internal symmetry.

This compound showcases the concept that even though a molecule may have chiral centers, it can still be classified as a meso compound if it possesses an internal plane of symmetry.


In addition to organic acids like tartaric acid, other types of compounds can also be considered meso compounds.

One such example is 2,3-dibromobutane. This molecule contains four carbon atoms and two bromine atoms and exhibits an internal plane of symmetry. Consequently, despite the presence of chiral carbons, 2,3-dibromobutane is classified as a meso compound.

Understanding these examples helps us grasp the concept of meso compounds better.

They highlight how certain molecules may appear optically active at first glance due to their chiral nature but fail to exhibit any optical rotation due to their internal symmetry.

Determining Optical Activity in Meso Compounds

To determine the optical activity of a compound, we need to consider its stereochemistry and the presence of chiral centers. However, Things are a bit different.

Meso compounds as a whole lack optical activity because they possess an internal plane of symmetry. This means that any rotation caused by one enantiomer is canceled out by the opposite rotation from its mirror image enantiomer within the molecule itself.

The presence of an internal plane of symmetry is what distinguishes meso compounds from other chiral compounds. It allows the opposing activities to balance each other out, resulting in no net optical rotation.

To identify whether a compound is meso or not, we need to examine its structure for the presence or absence of an internal plane of symmetry. If such a plane exists, then the compound is meso; otherwise, it is not.

By determining if a compound is meso or not, we can understand its physical properties and how it behaves in chemical reactions. While meso compounds may lack overall optical activity, their individual enantiomers can still be optically active.

Methods for Identifying Meso Compounds

To determine whether a compound is a meso compound, there are several methods that can be used. Let’s explore these methods in more detail:

Visual Inspection

One method involves visually inspecting the molecule to identify the presence or absence of an internal plane. In a meso compound, there is an internal plane that divides the molecule into two equal halves.

This means that if we were to fold the molecule along this plane, both halves would perfectly overlap each other.

Analyzing Molecular Models

Analyzing molecular models can also aid in recognizing symmetrical elements that define meso compounds.

By examining the three-dimensional structure of the molecule, we can identify any planes of symmetry or mirror planes. If such symmetrical elements are present, it suggests that the compound may be a meso compound.

X-ray Crystallography and Spectroscopic Techniques

For a more detailed confirmation, techniques like X-ray crystallography and spectroscopy can provide valuable structural information about a compound.

X-ray crystallography allows us to determine the exact arrangement of atoms within a crystal lattice, while spectroscopic techniques like Nuclear Magnetic Resonance (NMR) provide insights into chemical bonding and molecular connectivity.

By utilizing these methods, scientists can confirm whether a compound is indeed a meso compound or not.

It’s important to differentiate between meso compounds and other types of isomers such as chiral compounds and diastereomers.

Remember, determining whether a compound is meso requires careful analysis and consideration of its symmetrical properties using various experimental techniques.


Now that you have a clear understanding of meso compounds, you can confidently identify and differentiate them from other stereoisomers.

Remember, meso compounds possess an internal plane of symmetry which cancels out their optical activity. This unique property makes them fascinating molecules to study in the field of organic chemistry.

To further enhance your knowledge, consider exploring more examples of meso compounds and familiarize yourself with the various methods used to identify them.

By deepening your understanding, you will become better equipped to tackle complex problems and make accurate determinations regarding optical activity.

Keep expanding your expertise in organic chemistry by staying curious and engaged. Continue learning about different types of stereoisomers, their properties, and applications.

Experiment with hands-on activities or engage in discussions with fellow enthusiasts to broaden your perspectives. The world of organic chemistry is vast and ever-evolving, so embrace the journey of discovery!


What is the difference between a meso compound and a racemic mixture?

A meso compound is a type of stereoisomer that possesses an internal plane of symmetry, resulting in its lack of optical activity. On the other hand, a racemic mixture consists of equal amounts of two enantiomers (mirror-image isomers) that cancel out each other’s optical activity. While both meso compounds and racemic mixtures exhibit no net optical rotation, they differ in their molecular structures.

Can all chiral compounds be classified as either R or S?

No, not all chiral compounds can be classified as either R or S using the Cahn-Ingold-Prelog priority rules. Meso compounds are an exception because they possess an internal plane of symmetry that allows for identical substituents on both sides when viewed from different angles. As such, they cannot be assigned R or S configurations.

Are there any practical applications for meso compounds?

Yes! Meso compounds have practical applications in various fields, including pharmaceuticals, materials science, and catalysis. For example, meso compounds are often used as chiral building blocks for the synthesis of complex organic molecules in drug discovery. They play a crucial role in designing new materials with specific properties and enhancing the efficiency of certain chemical reactions.

How can I determine if a compound is meso without using symmetry?

While symmetry is the most straightforward way to identify meso compounds, you can also use other methods such as NMR spectroscopy or X-ray crystallography. These techniques provide detailed information about the molecular structure, allowing you to determine if a compound possesses an internal plane of symmetry. However, it’s important to note that these methods may require specialized equipment and expertise.

Are all meso compounds achiral?

Yes, all meso compounds are achiral due to their possession of an internal plane of symmetry. This symmetry cancels out any potential optical activity arising from their chiral centers. Therefore, despite having stereocenters within their structures, meso compounds do not exhibit enantiomeric properties and cannot rotate polarized light.

Can a molecule be both meso and optically active?

No, it is not possible for a molecule to be both meso and optically active. Meso compounds possess an internal plane of symmetry that cancels out their optical activity. In contrast, optically active compounds lack any form of internal symmetry and exhibit different rotations of polarized light depending on their enantiomeric forms (R or S).