Diastereomers - Meaning, Example, Properties, Differentiation, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:48 PM IST

The stereoisomers that are not related to objects and mirror images are called diastereomers which means that they are not enantiomers. Their mirror images of each other and non-superimposable. Diastereomers are entirely different in many aspects from enantiomers in their physical properties, the reactivity, their melting point, boiling points, densities, etc. are all different. But both the enantiomers and diastereomers are called stereoisomers.

This Story also Contains

Properties of Diastereomers
Properties of Diastereomers and Enantiomers
Diastereomers Example
Diastereoselectivity
Diastereomer Meaning
Superimposable Mirror Images

Properties of Diastereomers

Other than geometrical isomers, diastereomers may or may not be optically active.
Compared to enantiomers they all have a similar physical property except the sign of specific rotation is different but for diastereomers, they have different physical properties such as melting point, boiling point, refractive index, dielectric constant, specific rotation, density, etc. are all different.
As their physical properties are different, diastereomers can be separated from each other through some techniques like fractional crystallization, chromatography, fractional distillation, etc. While enantiomers cannot be separated by any of the above-mentioned techniques. This property can also be utilized in chiral synthesis.

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Properties of Diastereomers and Enantiomers

When talking about diastereomers and enantiomers tartaric acid, C₄H₆O₆ is a good example. The structure of tartaric acid is very interesting to study also. Tartaric acid is mainly in the form of (R, R). But it can also be in the meso form that is (R, S) by synthesizing artificially. (R, R) tartaric acid is the mirror image to (S, S) tartaric acid, that is they are enantiomeric in nature.

While the meso tartaric acid that is (R, S) is diastereomers to (R, R) tartaric acid. So, (R, R) and (S, S) tartaric acid are enantiomers so they have similar physical properties that their melting point is the same that is 170 degrees Celsius. While the case of meso tartaric acid is different, that is for (R, S) tartaric acid has different physical properties; their melting point is different from other stereoisomers and is about 145 degrees Celsius. The following image shows (R, R), (S, S), and (R, S) of tartaric acid.

Stereoisomers of tartaric acid

Diastereomers Example

Let us consider another compound possessing two chiral centers 3-Bromo-2-Butanol. From the following structure of 3-Bromo-2-Butanol, we get the facts that one of the configurations is mirror images to each other while the other is non-superimposable and is not mirror images.

Diastereomers and enantiomers of 3-Bromo-2-Butanol

The (R, S) and (S, R) are enantiomers, (R, R) and (S, S) are enantiomers while (R, S) and (S, S) are diastereomers, and (R, R) and (S, R) are diastereomers.

Therefore, these two configurations are not mirrored images to each other, and also they are not enantiomeric but are diastereomers. From the above-mentioned images, we get a clear-cut picture of diastereomers and also how they differ from enantiomers.

The diastereomers which are different from each other only by one stereocenter having two or more stereocenters are known as epimers. Examples of epimers are D-glucose and D-galactose. They are epimers of each other and as well as diastereomers.

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Diastereoselectivity

For an organic reaction, the preference for the formation of one or more diastereomers is its diastereoselectivity. That is for a chemical reaction when only one diastereomer is preferred over the other diastereomers then the reaction can be called a diastereoselective reaction. This happens when one of the sides is completely blocked by some other compounds. The best example of a diastereoselective reaction is the dehydrohalogenation of 2-iodo-butane. Where this reaction yields both trans and cis product while trans-2-butene is formed in excess that is 60% while cis-2-butene only 20%.

Erythro and Threo Form

Threo and erythro configurations are written when the molecule contains a chiral carbon. Chirality is a property when the mirror image of a molecule is different. If a molecule contains at least one chiral center the molecule is said to be chiral.

For naming molecules with two stereogenic centers erythro and threo forms are commonly used. The following figure tells about the erythro and threo form.

Erythro and threo form

Erythro and Threo Form

Related topics,

From the image, we can easily define erythro and threo forms. That is when the same groups R1 and R4 are on the same side it is called erythro form and when the common substituents R1 and R4 are on the opposite side it is called threo form. So we can define erythro form as, when common substituents lie on the same side it is called erythro form while they lie on the opposite side it is called threo form. This approach is mainly used for naming chiral compounds, mainly those having two chiral centers. It is commonly used for naming carbohydrates. The following compound is an example of erythro and threo forms.

Stereoisomers of 3-Bromo-2-Butanol

For 3-Bromo-2-Butanol when 2 H atoms are present on the same side it is called erythro form (first figure). When 2 H atoms are present on the opposite side it is called threo form (second figure).

For the case of simplicity erythro and threo form nomenclature is replaced with syn and anti stereoisomers that is when two common substituents are present on the same side it is called syn while present on opposite sides of the planes is called anti in a zig-zag carbon skeleton.

Let us consider another example that is 2, 3-dichloroethane. Here two chlorine atoms are present when the two chlorine atoms and hydrogen atoms are present on the same side it is an erythro compound that is erythro-2, 3-dichloroethane. While when two hydrogen atoms and chlorine atoms are present on opposite sides it is a threo compound that is threo-2, 3-dichloroethane. The name erythro and threo are obtained from the names of saccharides that are erythrose and threose. Thus by changing the position of the functional group there will be a great change in their properties. Erythro and threo compounds also have two enantiomeric forms which are represented as D and L enantiomers.

D and L Enantiomers

Diastereomer Meaning

Those stereoisomers that do not mirror images and are not superimposable are diastereomers. And they are not enantiomers.

Superimposable Mirror Images

Images that can superimpose are superimposable mirror images. The best example is the right and left hands of humans. Such compounds are called achiral molecules. And those objects and mirror images that cannot be superimposed are non-superimposable mirror images and are chiral compounds. The following is an example of a non-superimposable mirror image.

Superimposable mirror images

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Frequently Asked Questions (FAQs)

1. Optical isomers that do not mirror images are called?

Diastereomers. The stereoisomers that do not mirror images and are non-superimposable are diastereomers. Optical isomerism arises when they contain non-superimposable mirror images.

2. Are diastereomers optically active?

Diastereomers are a type of optical isomers so they are optically active. These do not mirror images and are not superimposable also.

3. What are diastereomers?

The compounds that are non-superimposable and are not related as object and mirror images are diastereomers. Diastereomers differ from enantiomers as enantiomers are objects and mirror images of each other.

4. What are diastereomers?

Diastereomers are stereoisomers that are not mirror images of each other. They have the same molecular formula and bonding sequence but differ in the spatial arrangement of atoms or groups around one or more chiral centers. Unlike enantiomers, diastereomers have different physical and chemical properties.

5. Give an example of diastereomers.

The compounds that are non-superimposable and are not related as object and mirror images are diastereomers. If we observe the structure of 3-Bromo-2-Butanol, we get the facts that one of the configurations is mirror images to each other while the other is non-superimposable and is not mirror images.

6. What are chiral compounds?

The compound is said to be chiral when they are mirror image of each other or a non-superimposable image.

7. Do diastereomers have a plane of symmetry?

Yes, diastereomers have a plane of symmetry with two chiral compounds.

8. What is meso compound and how does it relate to diastereomers?

A meso compound is a special type of diastereomer that has an internal plane of symmetry, making it optically inactive despite having chiral centers. Meso compounds are achiral overall and are their own diastereomers. They often occur in molecules with an even number of chiral centers.

9. What is the concept of diastereotopic groups and how does it relate to diastereomers?

Diastereotopic groups are chemically equivalent groups that would become diastereomers if one of them was replaced by a different substituent. They are not equivalent in a chiral environment and can show different chemical shifts in NMR spectra. Understanding diastereotopic relationships is crucial for predicting and interpreting the outcomes of stereoselective reactions.

10. What is a diastereomeric salt and how is it used in enantiomer separation?

A diastereomeric salt is formed when an enantiomeric mixture reacts with an optically pure chiral compound (resolving agent). The resulting diastereomeric salts have different physical properties and can be separated. After separation, the original enantiomers can be regenerated. This method, known as resolution, is widely used for separating enantiomers in organic synthesis.

11. What is a diastereomeric transition state and how does it influence reaction outcomes?

A diastereomeric transition state refers to the different spatial arrangements of atoms or groups in the transition state of a reaction. When a reaction can proceed through diastereomeric transition states, the one with lower energy is favored, leading to a predominance of one diastereomeric product. This concept is fundamental in understanding and predicting stereoselectivity in organic reactions.

12. Can you provide an example of diastereomers?

A common example of diastereomers is the pair of molecules 2-bromo-3-chlorobutane. This molecule has two chiral centers, resulting in four possible stereoisomers. Two of these stereoisomers are diastereomers of each other, while the other two form another diastereomeric pair.

13. What is the significance of diastereomers in natural product chemistry?

Diastereomers play a crucial role in natural product chemistry because many natural compounds contain multiple chiral centers, leading to complex diastereomeric relationships. Understanding these relationships is essential for structure elucidation, total synthesis, and studying the biological activities of natural products. Nature often produces specific diastereomers selectively, which can guide synthetic strategies.

14. What is the relationship between diastereomers and conformational isomers?

Diastereomers are distinct from conformational isomers. While diastereomers have different spatial arrangements that cannot be interconverted by rotation around single bonds, conformational isomers can interconvert through such rotations. However, some molecules can exhibit both diastereomeric and conformational relationships, adding complexity to their analysis.

15. What is the importance of diastereomers in asymmetric synthesis?

Diastereomers are crucial in asymmetric synthesis, where the goal is to produce one specific stereoisomer. By creating diastereomeric intermediates, chemists can control the stereochemistry of the final product. This is because diastereomers have different physical properties and reactivities, allowing for selective reactions or separations.

16. How do diastereomers influence the outcome of aldol reactions?

In aldol reactions, the formation of diastereomers can significantly affect the outcome. The reaction can produce syn and anti diastereomers, and the ratio between these is influenced by factors like the structure of the starting materials, the reaction conditions, and the presence of chiral catalysts. Understanding these diastereomeric relationships is crucial for predicting and controlling the stereochemistry of aldol products.

17. What is the significance of diastereomers in organic synthesis?

Diastereomers are significant in organic synthesis because they allow for the creation of specific three-dimensional structures. Controlling the formation of particular diastereomers (diastereoselectivity) is crucial in the synthesis of complex molecules, especially in the pharmaceutical industry where the spatial arrangement of atoms can greatly affect a drug's efficacy and safety.

18. How do diastereomers impact drug design and efficacy?

Diastereomers can have profound impacts on drug design and efficacy because different spatial arrangements of atoms can lead to different interactions with biological targets. One diastereomer might be therapeutically active while another could be inactive or even toxic. This is why understanding and controlling diastereomeric relationships is crucial in pharmaceutical development.

19. What is diastereomeric excess (de) and how is it calculated?

Diastereomeric excess (de) is a measure of the purity of a mixture of diastereomers. It is calculated as the difference between the amount of the major and minor diastereomers, divided by their sum, expressed as a percentage. The formula is: de = [(major - minor) / (major + minor)] × 100%. A higher de indicates a more selective reaction or purification process.

20. How do diastereomers affect chromatographic separation?

Diastereomers can often be separated using chromatographic techniques because they interact differently with the stationary phase. This difference arises from their distinct spatial arrangements, leading to varying retention times. This property is extensively used in analytical and preparative chemistry for the separation and purification of diastereomeric mixtures.

21. How do diastereomers affect a compound's reactivity?

Diastereomers can have different reactivities due to their distinct spatial arrangements. This can lead to differences in reaction rates, product distributions, and even the types of reactions they undergo. Understanding these differences is crucial in fields like pharmaceutical chemistry, where different diastereomers of a drug may have varying biological activities.

22. How do diastereomers impact the melting point of a compound?

Diastereomers typically have different melting points due to their distinct crystal packing arrangements. The melting point difference can be used as a method to distinguish between diastereomers and assess the purity of a diastereomeric mixture. Generally, the diastereomer with the more symmetrical structure tends to have a higher melting point.

23. How do diastereomers affect the solubility of a compound?

Diastereomers can have different solubilities due to their distinct spatial arrangements, which affect intermolecular interactions with the solvent. This property can be exploited for separation and purification purposes. The difference in solubility is often more pronounced in chiral solvents, where one diastereomer may interact more favorably with the solvent molecules.

24. How do diastereomers affect the boiling point of a compound?

Diastereomers typically have different boiling points due to their distinct intermolecular forces. The difference in spatial arrangement affects how the molecules interact with each other, leading to variations in the energy required to overcome these interactions during boiling. This property can be used for separation through distillation techniques.

25. How do diastereomers impact infrared (IR) spectroscopy?

Diastereomers can show differences in their IR spectra due to their distinct spatial arrangements. While the overall pattern may be similar, there can be subtle differences in peak positions and intensities, especially in the fingerprint region. These differences arise from variations in bond angles and intermolecular interactions specific to each diastereomer.

26. How do diastereomers affect NMR spectra?

Diastereomers produce different NMR spectra because the spatial arrangement of atoms affects the chemical environment of the nuclei. This results in different chemical shifts, coupling constants, and peak patterns for diastereomers. NMR spectroscopy is thus a powerful tool for distinguishing between diastereomers and determining their relative configurations.

27. How do diastereomers differ from enantiomers?

Diastereomers differ from enantiomers in that they are not mirror images of each other. While enantiomers have identical physical properties (except for the direction they rotate plane-polarized light), diastereomers have different physical properties such as melting point, boiling point, and solubility.

28. How can diastereomers be distinguished experimentally?

Diastereomers can be distinguished experimentally through various methods due to their different physical properties. These include measuring melting points, boiling points, solubility, and using spectroscopic techniques such as NMR spectroscopy, which can show different chemical shifts for diastereomers.

29. Can diastereomers be separated by simple distillation?

Yes, diastereomers can often be separated by simple distillation because they have different boiling points. This is in contrast to enantiomers, which have identical boiling points and cannot be separated by distillation. The difference in boiling points arises from the different intermolecular forces between diastereomers due to their distinct spatial arrangements.

30. What is the relationship between diastereomers and optical activity?

Diastereomers can have different optical activities. While some diastereomers may be optically active (rotate plane-polarized light), others may be optically inactive. This is because optical activity depends on the overall molecular symmetry, not just the presence of chiral centers. Meso compounds, for example, are diastereomers that are optically inactive due to an internal plane of symmetry.

31. What is the relationship between the number of chiral centers and the number of possible diastereomers?

The number of possible diastereomers increases with the number of chiral centers. For a molecule with n chiral centers, the maximum number of stereoisomers is 2^n. The number of diastereomers is then calculated by subtracting the number of enantiomeric pairs from the total number of stereoisomers.

32. What is the concept of diastereoselectivity in organic reactions?

Diastereoselectivity refers to the preferential formation of one diastereomer over another in a reaction that creates a new stereocenter. It's influenced by the existing stereocenters in the molecule and the reaction conditions. High diastereoselectivity is often desired in organic synthesis to obtain pure, stereochemically defined products.

33. How do diastereomers affect the refractive index of a compound?

Diastereomers often have different refractive indices due to their distinct spatial arrangements, which affect how light interacts with the molecules. This property can be used as another method to distinguish between diastereomers and assess the purity of a mixture. The difference in refractive index is typically small but measurable with precise instruments.

34. What is the concept of matched and mismatched pairs in diastereomeric reactions?

Matched and mismatched pairs refer to the stereochemical relationship between reactants in reactions involving multiple chiral centers. In a matched pair, the stereochemistry of the reactants works cooperatively to favor one diastereomeric product. In a mismatched pair, the stereochemical elements work against each other, often leading to lower selectivity or yield. This concept is important in understanding and predicting the outcomes of stereoselective reactions.

35. How do diastereomers affect the crystal structure of a compound?

Diastereomers often form different crystal structures due to their distinct spatial arrangements. This can lead to differences in properties like solubility, melting point, and even color. X-ray crystallography can be used to determine the absolute configuration of diastereomers by analyzing their crystal structures, which is particularly useful in structure elucidation of complex molecules.

36. What is the significance of diastereomers in kinetic resolution?

Kinetic resolution is a process where one enantiomer in a racemic mixture reacts faster than the other with a chiral reagent or catalyst. This process creates diastereomeric transition states, leading to diastereomeric products or intermediates. The difference in reaction rates allows for the separation of enantiomers, making kinetic resolution an important tool in asymmetric synthesis and chiral separations.

37. How do diastereomers affect the optical rotation of a compound?

Diastereomers can have different optical rotations due to their distinct spatial arrangements. While enantiomers rotate plane-polarized light in equal but opposite directions, diastereomers can rotate light to different extents and even in the same direction. This property can be used to distinguish between diastereomers and monitor the progress of stereoselective reactions.

38. What is the concept of diastereotopic faces in organic molecules?

Diastereotopic faces refer to the two sides of a planar functional group (like a carbonyl) that would lead to diastereomers if attacked from different sides. Understanding diastereotopic faces is crucial in predicting the stereochemical outcome of addition reactions. The preferential attack on one face over the other can lead to the formation of one diastereomer predominantly.

39. How do diastereomers impact the efficiency of chiral HPLC separations?

Diastereomers can often be separated more easily than enantiomers using chiral HPLC (High-Performance Liquid Chromatography). This is because diastereomers have different physical properties and interact differently with the chiral stationary phase. The efficiency of separation depends on the nature of the diastereomers and the choice of the chiral column, making diastereomeric relationships important in developing effective HPLC methods.

40. What is the role of diastereomers in dynamic kinetic resolution?

Dynamic kinetic resolution (DKR) is a process that combines kinetic resolution with in-situ racemization of the slower-reacting enantiomer. This process often involves the formation of diastereomeric intermediates. Understanding the diastereomeric relationships in DKR is crucial for optimizing reaction conditions and achieving high yields of a single enantiomeric product.

41. How do diastereomers affect the outcome of cycloaddition reactions?

In cycloaddition reactions, such as the Diels-Alder reaction, the formation of diastereomers can significantly influence the outcome. The spatial arrangement of reactants can lead to endo and exo diastereomers, with one often being favored due to secondary orbital interactions. Understanding these diastereomeric relationships is crucial for predicting and controlling the stereochemistry of cycloaddition products.

42. What is the concept of diastereomeric complexes in coordination chemistry?

Diastereomeric complexes in coordination chemistry refer to metal complexes that have the same chemical formula and bonding sequence but differ in the spatial arrangement of ligands. These complexes can have different properties and reactivities. Understanding diastereomeric relationships in metal complexes is important in fields like catalysis and materials science.

43. How do diastereomers impact the effectiveness of chiral auxiliaries?

Chiral auxiliaries are used to control the stereochemistry of reactions by creating diastereomeric intermediates. The effectiveness of a chiral auxiliary depends on its ability to create a significant energy difference between diastereomeric transition states, leading to the preferential formation of one diastereomer. After the reaction, the auxiliary is removed, leaving the desired enantiomerically pure product.

44. What is the significance of diastereomers in total synthesis of natural products?

In total synthesis of natural products, controlling the formation of specific diastereomers is often crucial. Many natural products have multiple chiral centers, and synthesizing the correct diastereomer is essential for matching the biological activity of the natural compound. Strategies like using chiral starting materials, stereoselective reactions, and late-stage modifications are employed to control diastereomeric relationships throughout the synthesis.

45. How do diastereomers affect the outcome of nucleophilic addition reactions to carbonyls?

In nucleophilic additions to carbonyls, the formation of diastereomers can be influenced by factors like steric hindrance and chelation control. For example, in the addition of a Grignard reagent to an α-chiral aldehyde, the Cram or Felkin-Anh models predict the favored diastereomer based on the spatial arrangement of substituents. Understanding these models is crucial for predicting and controlling the stereochemical outcome of such reactions.

46. What is the concept of diastereomeric resolution and how is it applied?

Diastereomeric resolution is a technique used to separate enantiomers by converting them into diastereomers. This is typically done by reacting the enantiomeric mixture with an enantiomerically pure compound (resolving agent). The resulting diast