Homologous Series: Isomerism – Structural and Stereoisomerism

Introduction –

A homologous series is a collection of molecules that have chemical characteristics and functional groups that are similar to one another but differ by the presence or absence of CH2 between them. Carbon chains of varying lengths have been discovered in organic molecules with the same general formula, but with slightly different structures.

In the first place, a series of organic compounds is made up of organic compounds that differ from one another by a repeating unit while having the same general formula in the second. The alkanes with the general formula CnH2n+2, the alkenes with the general formula CnH2n, and the alkynes with the general formula CnH2n-2 are the building blocks of the most fundamental homologous series in organic chemistry.

Exemplifications of homologous series

Each subsequent member differs from the preceding member by one CH2 unit. 

The difference between CH4 and C2H6 is a -CH2 unit, and the difference between C2H6 and C3H8 is also a -CH2 unit. 

The difference between CH4 and C3H8 is a -CH2 unit. As a result, CH4, C2H6, and C3H8 are all homologous to one another in structure. 

The same effect can be observed in alkenes containing ethene as the first member and C3H6, C4H8, and C5H10 as the subsequent members. 

Alkenes contain ethene as the first member and C3H6, C4H8, and C5H10 as the subsequent members. 

They are distinguished from one another by the presence of a –CH2 unit. Alkenes are represented by the formula CnH2n.

Functional groups are consistent across all members of this series. 

They have identical physical properties, and their mass increases in a fixed gradation as they gain mass. As the molecular mass of subsequent members of the series increases, the characteristics of CH3OH, C2H5OH, and C3H7OH become more similar and gradually differ from one another. Due to the fact that the molecular mass of the compounds increases, so does the number of bonds in the compounds, this is the case.

 A consequence of this is that as the molecular masses of a compound increase, properties such as melting and boiling points, solubility, and other properties that are dependent on the mass and total number of bonds in the compound gradually change. Despite the fact that they all have the same functional groups, the chemical characteristics of members of homologous series are identical because they share the same functional groups.

What exactly is Isomerism, and how does it function?

This occurs when two or more compounds have the same chemical formula but different chemical structures, and the phenomenon of isomerism results from this.

The chemical compounds known as isomers have the same chemical formulae but differ in their physical and chemical properties as well as their atom arrangement in the molecule. As a result, substances that exhibit isomerism are referred to as isomers when they exist in nature.

A composite word derived from the Greek words “isos” and “meros,” which both mean “equal pieces” or “equal parts.” It was first used in 1830 by the Swedish chemist Jacob Berzelius to describe a chemical reaction.

Isomerism can be classified into several categories.

Each of the two main types of isomerism can be further subdivided into subgroups, and each of these subgroups can be further subdivided. The two most common types of isomerism are structural isomerism and stereoisomerism. The classification of various types of isomers is depicted in the diagram below.

In Structure, there is some isomerism.

Constitutional isomerism is a term that refers to structural isomerism in its most general sense. The functional groups and atoms in the molecules of these isomers are connected in a variety of ways. Because structural isomers may or may not contain the same functional group, the International Union of Pure and Applied Chemistry (IUPAC) assigns them different designations.

The various types of structural isomerism are discussed in detail in this section.

• Using Isomerism to Break the Chains
• Skeletal isomerism is another term for this phenomenon.
• The constituents of these isomers have distinctly different branching architectures.
• In the majority of cases, the branching of carbon in chain isomers differs.
• Positional Isomerism Positional isomers differ in the locations of functional groups or substituent atoms in their ligands.
• This isomerism is characterised by the attachment of functional groups to distinct carbon atoms throughout the carbon chain….
• This type of isomerism can be found in compounds with the formula C3H7Cl, which are commonly found in chlorine compounds.

In a functional sense, isomerism is useful.

Another term for this phenomenon is functional group isomerism.

As the name implies, it refers to compounds that have the same chemical formula but have different functional groups linked to them, rather than the other way around.

Functional isomerism can be seen in the chemical molecule C3H6O, which stands for carbon, hydrogen, and oxygen.

Metamerism

As a result of the presence of distinct alkyl chains on either side of the functional group, this type of isomerism occurs.

It’s a rare type of isomerism that only occurs in compounds containing a divalent element (such as sulphur or oxygen) that is surrounded by alkyl groups, according to the IUPAC definition.

C4H10O is found in a variety of compounds, including ethoxyethane (C2H5OC2H5) and methoxy-propane (C4H10O) (CH3OC3H7).

Tautomerism

A tautomer is an isomer of a chemical that differs only in the location of protons and electrons and is distinguished from other isomers by this property.

The majority of the time, the tautomers of a compound coexist in equilibrium and are easily interchangeable.

It occurs as a result of a proton transfer occurring within the molecule.

The phenomenon of keto-enol tautomerism is an excellent illustration of this phenomenon.

In a ring-chain, there is isomerism.

In ring-chain isomerism, one isomer has an open-chain structure, whereas the other has a ring structure, resulting in a binary isomer.

They typically contain a range of different amounts of pi bonds.

The isomerism in the compound C3H6 is a fantastic example of this type of isomerism in action. Propene and cyclopropane are the isomers that result as a result of this reaction.

Stereoisomerism

This type of isomerism occurs in compounds that have the same chemical formula but differ in the three-dimensional orientations of the atoms that make up their molecules. Stereoisomers are chemicals that exhibit the property of stereoisomerism. A further division can be made between this phenomenon’s two categories. This subsection provides a brief overview of both of these classifications.

Geometric Isomerism

 is a mathematical concept.

Cis-trans isomerism is the term used to describe this phenomenon.

These isomers have different spatial configurations of atoms in three-dimensional space, which makes them different from one another.

This diagram illustrates the geometric isomerism that was discovered in the acyclic graph. But-2-ene is a molecule that can be found in but-2-ene, which is a compound.

Optical Isomerism- 

is a type of optical isomerism that can be found in nature.

When a compound has comparable bonds but differing spatial arrangements of atoms, optical isomerism occurs, resulting in non-superimposable mirror images of the same substance.

Enantiomers are another name for optical isomers, which are the same thing.

It is possible to distinguish between enantiomers by their optical activity.

The dextro enantiomers rotate the plane of polarized light to the right, whereas the laevo enantiomers rotate the plane of polarized light to the left, and vice versa.

Ionization is characterized by isomerism.

Chemical compounds that produce different ions in solution despite having the same composition are referred to as ionization isomers. This property is referred to as ionization isomerism. Despite having the same chemical composition, ionization isomerism describes compounds that produce distinct ions in solution despite having the same chemical composition. It is possible for the counter ion in a complex salt to also act as a potential ligand, in which case it can displace a ligand, which can then act as the counter ion, resulting in isomerism of the complex salt.

[Co(NH3)5SO4]Br and [Co(NH3)5Br] are two examples of cobalt halides.

Sodium SO4 and potassium SO4 are two examples of ionization isomerism.

To create these ionization isomers, the procedure outlined below can be followed.

[CoBr(NH3)5]

[CoBr(NH3)5] SO4

RedViolet = 2+ + SO42 = Red Violet

[CoSO4(NH3)5]

[CoSO42(NH3)5] [CoSO42(NH3)5] [CoSO42(NH3)5] [CoSO42(NH Br = Red] CoSO42(NH Br = Red

Conclusion-

 A homologous series is a collection of molecules that have a similar appearance and share the same functional group, as well as possessing similar properties.