What is Stereochemistry in Chemistry?
Stereochemistry, an important subcategory of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. For this reason, it is also known as 3D chemistry in which the prefix "stereo" means "three-dimensionality".
Using this formulation of stereochemistry procedures, any chemist can work out the relationships between different molecules that are made up of the same category of atoms. They can even study the effect on the physical or biological properties these relationships give molecules. An important part of stereochemistry is the study of chiral molecules and this serves as a really useful part of the chemistry to the students which might help them in the future.
Chemistry is really important and efficient for the research and study of living organisms because it helps students and scientists to understand the life processes of every living thing on earth at the molecular level. At any molecular level, every process of life takes place due to the involvement of various minor or major chemical reactions.
Thus, it is important for the students to learn their chapters well and understand all the chemistry concepts by practicing with a maximum number of past years’ question papers and sample question papers available on the Vedantu website. This will help them to understand the time management skill and learn the marking schemes that carry maximum marks and plan which question needs what type of answers. Break down larger portions into smaller effective points and write them down in a separate notebook so it will help you in revising before the exams. Make note of the important questions that keep repeating in the recent past year question papers and give more weightage to those questions and prepare a little extra because it might repeat in the current year also. If you have any doubts about the equations and chemical formulations that are taught during the classes then try to spend some extra time in the lab and get to understand all the concepts by trying out the experiments and practicing them really well. This will definitely help you write your formulas and equations really well.
Brief About Stereochemistry
Stereochemistry is defined as the branch of chemistry which involves “the study of various spatial arrangements of atoms present in molecules”.
Stereochemistry is described as the systematic presentation of a particular field of science and technology traditionally requiring a short preliminary excursion into history. Stereochemistry is also called the ‘chemistry of space ‘, which is stereochemistry that deals with the spatial arrangements of groups and atoms in a molecule.
More about Stereochemistry
Stereochemistry is capable of tracing its roots to 1842 when the French chemist, named, Louis Pasteur made an observation, which the salts of tartaric acid collected from a vessel of wine production which has the ability to rotate plane-polarized light, whereas similar salts from various sources did not hold this ability. This whole phenomenon is explained by optical isomerism.
Types of Stereoisomers
Different types of stereoisomers are tabulated below. Let us discuss more about them.
Stereoisomerism
Stereoisomerism is known as “the isomerism, which is caused by the non-similar arrangements of functional groups or atoms that belong to an atom in space”. These kinds of isomers contain similar constitutions, but various geometric arrangements of atoms. Stereoisomers are broadly classified into two types, which are enantiomers and diastereomers.
Enantiomers
When two isomers are explained as the mirror images of each other, such type of isomerism is known as enantiomerism, and these types of isomers are called enantiomers.
Enantiomers are the isolable and stable compounds that vary in their spatial arrangements in 3-D space.
Generally, they exist as discrete pairs.
The properties of enantiomers are identical. However, their interaction with any plane of the polarized light can differ.
The direction, towards which they rotate the plane-polarized light is much different, it means, if one rotates in the right direction, the other rotates towards the left direction.
Diastereomers
When any two isomers are not behaving as mirror images of each other, they are referred to as diastereomers.
A molecule with an ‘n’ number of asymmetric carbon atoms can have up to ‘2n’ diastereomers.
When two diastereomers vary at only one stereocenter, they are called epimers.
These isomers change in both physical properties and chemical reactivity.
A representation of enantiomers which are mirror images of each other is given below.
Importance of Stereochemistry - Thalidomide Disaster
The atoms arrangement in three-dimensional space plays a major part in the molecule properties.
An example of the stereochemistry significance is observed in the thalidomide disaster which struck Germany in 1957.
This drug thalidomide was sold in the form of an over-the-counter drug, where it was initially intended to combat nausea. It can also be used by pregnant women to alleviate morning sickness.
However, it was discovered that this drug underwent racemization and was produced as an enantiomers mixture in the human body because of the metabolism process.
One of these enantiomers can be believed to cause some genetic damage in the development of embryos and lead to baby birth defects.
This is based on the data that over 5000 babies were born with the deformed limbs shortly after thalidomide sold commercially as an over-the-counter drug.
This unforeseen effect of the drug has led to the imposition of stricter drug regulation laws (only 40 per cent of the born babies with these deformities survived).
This disaster signifies stereochemistry's importance.
Facts about Stereochemistry
The structure of the molecule can change according to the three-dimensional arrangement of the atoms that constitute this. Also, Stereochemistry deals with the atom’s arrangement manipulation.
Commonly, this branch of chemistry can be referred to as 3-D chemistry because it focuses on the stereoisomers (which are the chemical compounds with similar chemical formulas but with a different spatial arrangement in these three dimensions).
A branch of stereochemistry deals with the molecule’s study that exhibits chirality, which is a property of the geometry of molecules that makes them non-superimposable on their mirror images.
Another branch of the three-dimensional chemistry, which is called dynamic stereochemistry, involves the study of the effects of various spatial arrangements of the atoms, present in a molecule on the rate of a chemical reaction.
Stereochemistry and Regiochemistry
The arrangement of stereoisomers can be described by stereochemistry. The key distinction between stereochemistry and regiochemistry is, the final result’s atomic structure of a chemical reaction can be represented using regiochemistry, whereas stereochemistry describes the atomic arrangement and the modification of these molecules.
FAQs on Stereochemistry
1. What is stereochemistry and why is it often called 3D chemistry?
Stereochemistry is a branch of chemistry that studies the three-dimensional arrangement of atoms within molecules. It is often called 3D chemistry because it focuses on how a molecule's spatial structure affects its physical and chemical properties. Unlike a simple chemical formula that only shows which atoms are present, stereochemistry describes their exact orientation in space.
2. What are the main types of stereoisomers?
Stereoisomers are molecules with the same molecular formula and connectivity but different spatial arrangements. They are primarily classified into two main types:
- Enantiomers: These are stereoisomers that are non-superimposable mirror images of each other. They have identical physical properties except for the direction in which they rotate plane-polarised light.
- Diastereomers: These are stereoisomers that are not mirror images of each other. This category includes geometric isomers (cis-trans or E/Z) and compounds with multiple chiral centres that are not enantiomers.
3. What is the key difference between enantiomers and diastereomers?
The fundamental difference lies in their mirror-image relationship. Enantiomers are perfect, non-superimposable mirror images of each other, like a left and right hand. Diastereomers, on the other hand, are stereoisomers that are not mirror images. Because of this, enantiomers have identical physical properties (like melting point and boiling point), while diastereomers have completely different physical properties.
4. What is chirality and how do you identify a chiral molecule?
Chirality is the geometric property of a molecule that makes it non-superimposable on its mirror image. The most common way to identify a chiral molecule is to look for a chiral centre, which is typically a carbon atom bonded to four different groups. If a molecule has a chiral centre and lacks a plane of symmetry, it is considered chiral.
5. How are R/S configurations assigned in stereochemistry?
The R/S system (from the Latin words Rectus and Sinister) is used to assign the absolute configuration of a chiral centre. The process involves two steps:
- Assigning Priority: The four groups attached to the chiral carbon are ranked based on atomic number (higher number gets higher priority) according to the Cahn-Ingold-Prelog (CIP) rules.
- Determining Configuration: The molecule is oriented so the lowest-priority group points away from the viewer. If the path from the highest priority (1) to the third-highest (3) is clockwise, the configuration is R. If the path is counter-clockwise, the configuration is S.
6. What do the D and L notations represent in stereochemistry?
The D/L notation is a system of relative configuration, primarily used for carbohydrates and amino acids. It compares the structure of a molecule to a reference molecule, glyceraldehyde. If the -OH (for sugars) or -NH₂ (for amino acids) group on the chiral carbon farthest from the carbonyl group is on the right side in a Fischer projection, it is assigned the D configuration. If it is on the left, it is assigned the L configuration. This system does not directly relate to optical rotation (+/-).
7. Why is stereochemistry critically important in the pharmaceutical industry?
Stereochemistry is vital in medicine because the two enantiomers of a drug can have vastly different biological effects. Our bodies are chiral environments, and enzymes and receptors are shaped to interact with specific 3D structures. One enantiomer might be a highly effective treatment, while its mirror image could be inactive or, in some cases, harmful. The tragic example of thalidomide, where one enantiomer was a sedative and the other caused birth defects, highlights the critical need to understand and control stereochemistry in drug development.
8. Can a molecule have chiral centres but still be achiral overall?
Yes, a molecule can have multiple chiral centres and still be achiral. This occurs in compounds known as meso compounds. A meso compound has two or more chiral centres but is achiral because it possesses an internal plane of symmetry that makes the molecule superimposable on its mirror image. Essentially, the optical activity of one chiral centre is cancelled out by the opposite activity of another within the same molecule.
9. Why are racemic mixtures optically inactive even though they contain chiral molecules?
A racemic mixture is a 50:50 mixture of two enantiomers. While each enantiomer on its own is optically active and rotates plane-polarised light, they rotate it in equal amounts but in opposite directions. The dextrorotatory (+) enantiomer's rotation is perfectly cancelled out by the levorotatory (-) enantiomer's rotation. This results in a net optical rotation of zero, making the overall mixture optically inactive.
10. How do E/Z notations for geometric isomers relate to stereochemistry?
E/Z notation is a part of stereochemistry used to describe the absolute configuration of double bonds in alkenes. It is a more universal system than cis/trans. Using the Cahn-Ingold-Prelog (CIP) priority rules, we assign priorities to the two groups on each carbon of the double bond. If the two higher-priority groups are on opposite sides of the double bond, it is designated E (from the German 'entgegen', meaning opposite). If they are on the same side, it is designated Z (from 'zusammen', meaning together).
