Brief Notes on Optical Isomerism

What are optical isomers?

Isomers are molecules that have the same molecular formula but differ in their atomic arrangements.

The four groups can be anything from a hydrogen atom to a chlorine atom, and they can be anything in between.

Remember:

There must be four groups, each of which must be distinct.

The plane of plane-polarised light can be rotated by optical isomers. When looking at a problem from above:

The (–) enantiomer rotates the plane clockwise, while the (+) enantiomer rotates it anticlockwise (to the left) (to the right).

A mixture containing equal amounts of (+) and (–) enantiomers is not optically active, meaning it won’t rotate the plane of polarisation. A racemic mixture, or racemate, is what it’s called.

Isomerism can be divided into two types.

• Isomerism in structure
• Stereoisomerism

Isomerism in structure

The molecular formula of structural isomers is the same, but the structural formulae are different. Remember that a molecular formula shows the number of atoms in a molecule or compound, whereas a structural formula goes a step further by displaying the unique arrangement of those atoms.

Propane, for example, has a molecular formula but a structural formula. We can see how the structural formula is derived by looking at its bonding: propane contains a carbon attached to three hydrogens, joined to carbon with two hydrogens, and then joined to another carbon with three hydrogens.

Structural isomers are divided into three categories.

• In the skeleton of the molecule, chain isomers have different arrangements of carbon atoms.
• The functional group is attached to a different location on the carbon chain in position isomers.
• The functional groups of functional group isomers differ.

Stereoisomerism

Stereoisomers share the same molecular and structural formulas, but their atoms are arranged differently in space. Their functional groups and carbon chains are identical, but their bonding is arranged differently. There are a variety of types.

• Around a C = C double bond, geometric isomers have different arrangements of atoms.
• Molecular optical isomers are non-superimposable mirror images of one another.

Isomers come in a variety of forms

Homomers are molecules that have the same chemical formula, are superimposable, and have the same connectivity.

Constitutive (or structural) isomers are molecules with the same chemical formula but different connectivity. They’re chemical compounds that have the same molecular formula but different structural formulas. Due to the different bonds between the elements that make up the molecule, this implies different physical and chemical properties.

The following are examples of constitutional isomers:

Chain isomers: that differ in the structure of the carbon “skeleton,” i.e. the presence and position of ramifications or rings, are known as chain isomers. This type of isomer has different physical properties, but chemical reactivity is often quite similar.

Positional isomers: Isomers that differ in the position of the functional group are known as positional isomers. This type of isomer has different physical properties, but chemical reactivity is often similar.

Functional isomers: are isomers with the same molecular formula (that is, the same number of atoms of the same elements) but dissimilar groupings because the atoms are connected in different ways.

What are Stereoisomers 

Stereoisomers are molecules that have identical chemical formulas and connectivity, but their atoms are arranged differently in space, making them non-superimposable.

Stereoisomers can be any of the following:

• Geometric isomers are molecules that have a C=C bond between two different groups (or cis or trans).
• The possible orientations given by the rotation of a C-C bond and the possible conformations of a molecule result in molecules with the same brute formula, equal connectivity, but not overlapping. Conformer or rotamer are other terms for conformational isomers. At room temperature, the energy barrier between the various orientations is very small, and one transforms into the other, despite the fact that each has a different level of stability.
• Molecules containing stereogenic elements are known as configurational or optical isomers.

What is isomerism?

Isomerism is a phenomenon in which different substances have the same brute formula, or molecular mass and atom percentage composition, for physical properties and, in some cases, chemical behaviour.

Isomerism in structure

The molecular formula of structural isomers is the same, but the structural formulae are different. Remember that a molecular formula shows the number of atoms in a molecule or compound, whereas a structural formula goes a step further by displaying the unique arrangement of those atoms.

What causes optical isomerism in the first place?

Molecular molecules with a carbon atom attached to four different groups cause optical isomerism. The carbon atom is known as a chiral centre or asymmetric carbon. An asterisk is frequently used to indicate it.

Conclusion

Understanding isomerism has aided in the development of both new and existing drug alternatives that are safer and more effective. Many already-existing drugs have gone through chiral switching. In which the racemic mixture has been replaced by one of its isomers.