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Isomers in chemistry are molecules or polyatomic ions with identical molecular formulae- that is, the same number of atoms of each element- but distinct atomic arrangements in space. Isomerism refers to the presence or absence of isomers. Isomers do not always have the same chemical or physical properties. The two main types of isomerism are structural or constitutional isomerism, which occurs when the bonds between the atoms differ, and stereoisomerism or spatial isomerism, which occurs whenever the bonds seem the same but the relative positions of the atoms differ. A hierarchy of isomeric relationships exists. Two chemicals may be the same constitutional isomer, but upon closer inspection, they are stereoisomers of each other. Two molecules with the same stereoisomer may have different conformational forms or be different isotopologues. The scope of the analysis is determined by the field of study or the chemical and physical properties of interest.
Overview
In general, organic compounds, molecules formed around a chain of carbon atoms (also known as the carbon backbone), are essential in the chemistry of life. These molecules are significant because of the energy they carry, which is primarily in the form of potential energy between atomic molecules. Because such potential forces can be greatly affected by changes in atomic placement, it is critical to understand the concept of an isomer, which is a molecule that has the same atomic make-up as another but differs in structural arrangements.
Organic chemistry is three-dimensional, which is one of its most intriguing aspects. In space, a molecule can have a shape that influences its properties. Molecules can differ in the way their atoms are arranged – the same atom combination can be assembled in multiple ways. These compounds are referred to as isomers. Isomers are molecules that have the same molecular formula but different atom arrangements.
A more subtle analogy is that one’s hands can be thought of as isomeric. Each hand has the same types of fingers, but a right hand can never be perfectly superimposed on a left hand; they are distinct. Isomerism is also affected by timing and energy. Molecules are mobile entities that undergo a variety of rotational motions that alter their shapes, and these motions require energy. As a result, some molecules may be identical on one timescale or set of energy conditions but different, or isomeric, on others. Finally, an isomer must have minimum energy; it must be in an energy well.
Isomerism
Isomerism implies the existence of molecules that have the same number of atoms of the same type (and thus the same formula) but differ in chemical and physical properties. Isomer derives from the Greek isos plus meros, which means “equal parts.” In simpler terms, isomers are chemical compounds that have the same parts but are not the same.
Isomerism is classified into two main types, each of which has several subtypes. Structural isomerism and stereoisomerism are the two most common types.
Constitutional isomerism is another name for structural isomerism. We can say that the functional groups and atoms in these isomers’ molecules are linked in various ways. As structural isomers may or may not contain the same functional group, they are given different IUPAC names.
Stereoisomers
Stereoisomers are molecules with the same molecular structure but a different three-dimensional spatial arrangement of the atoms. These are classified as enantiomers and diastereomers. Different enantiomers bind to different receptors, resulting in potentially different reactions. As a result, stereoselective separation methods are useful in the pharmaceutical, food, and agricultural industries.
All isomers can be classified as constitutional isomers or stereoisomers, with several subcategories within the stereoisomer category.
Stereoisomerism occurs in compounds that have the same chemical formula but different orientations of atoms in three-dimensional space. Stereoisomer compounds are frequently referred to as stereoisomers. This mechanism is further classified into two subtypes.
- Optical isomerism
- Geometrical isomerism
Optical isomerism
Optical isomerism occurs when two isomers have the same molecular weight as well as chemical and physical properties. They differ, however, in their effect on the rotation of polarised light.
Optical isomerism is most common in substances that have the same molecular and structural formula but cannot be superimposed on one another. To put it simply, they are mirror images of each other. It can also be found in substances containing an asymmetric carbon atom.
Stereoisomers that rotate the plane of polarised light are commonly used to demonstrate optical isomerism. If the plane of polarised light passing through enantiomer solution rotates clockwise, the enantiomer is said to exist in (+) form, and if the plane of polarised light rotates anti-clockwise, the enantiomer is said to exist in (-) form (-).
The rotation extent of plane-polarized light by the two enantiomeric forms is identical, but the rotation direction is opposite. Furthermore, if both enantiomer pairs are present in equal amounts, the resulting mixture is referred to as a racemic mixture. It means that half of the mixture exists in (+) form, while the other half exists in (-) form.
Because the racemic mixture rotates the plane of polarised light in the opposite direction equally, the net rotation remains zero. As a result, the racemic mixture has no optical activity.
When a chemical sample contains molecules of only one chirality within the detection limits, it is said to be enantiopure (also known as enantiomerically pure).
Geometrical isomerism
Geometrical isomerism is a type of stereoisomerism in which the molecular formula and structure are the same but the relative arrangement of atoms differs. Geometrical Isomerism is a common occurrence in heteroleptic complexes. Geometric Isomerism is exhibited by molecules whose spatial positions are locked to one another due to the presence of a ring structure or a double bond. This type of isomerism occurs as a result of the ligand’s various geometric arrangements.
Cis-2-butene and trans-2-butene are the most basic geometric isomers. The double bond in each molecule is formed by carbons 2 and 3. The methyl groups attached to carbons 2 and 3 are on the same side of the rigid double bond in cis-2-butene. The methyl groups in trans-2-butene are on opposite sides of the double bond.
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FAQs
What is isomerism in organic chemistry?
In organic chemistry, isomerism is a phenomenon characterized by two or more organic compounds with the same molecular formula but different properties due to differences in atom arrangement along with the carbon skeleton or in space.
What are isomers in organic chemistry?
Isomers are chemical compounds that have identical chemical formulae but differ in properties and atom arrangement in the molecule.
What are the types of isomerism?
The two main types of isomerism are structural or constitutional isomerism, which occurs when the bonds between the atoms differ, and stereoisomerism or spatial isomerism, which occurs when the bonds are similar but the relative positions of the atoms differ.
