Question

A similarity between optical and geometrical isomerism is that (a) If in a compound, one is present then so is the other. (b) Each forms equal number of isomers for a given compound (c) Both are included in stereoisomerism (d) They have no similarly

Short answer

Both optical and geometrical isomerism are part of stereoisomerism, as stated in option (c).

Step-by-step solution

Understand Isomerism

Isomerism is a phenomenon where compounds have the same molecular formula but different structural or spatial arrangements. There are two main types of isomerism: structural isomerism and stereoisomerism.

Define Optical Isomerism

Optical isomerism occurs when a compound can exist in two non-superimposable mirror images. These isomers are known as enantiomers and have a property of rotating plane-polarized light differently.

Define Geometrical Isomerism

Geometrical isomerism occurs due to restricted rotation around a bond, such as a double bond or a ring structure, leading to the formation of cis-trans isomers.

Identify Commonality

Both optical and geometrical isomerism fall under stereoisomerism. Stereoisomers have the same sequence of bonded atoms, but differ in the three-dimensional orientations of their atoms in space.

Evaluate Options

Analyze the options to identify that both optical and geometrical isomerism are included in stereoisomerism, matching option (c). Option (a) and (b) are incorrect because there is no intrinsic requirement for one type of isomerism to necessitate the presence of the other, and they don't generally form equal numbers of isomers.

Key concepts

Optical Isomerism

Optical isomerism is a fascinating aspect of stereochemistry, rooted in the concept of chirality. To picture chirality, think about your hands; they are mirror images but cannot be superimposed. This is similar to optical isomers, also known as enantiomers. These enantiomers have identical physical properties, such as melting and boiling points, but they differ in the way they interact with polarized light.

When plane-polarized light passes through a solution of an enantiomer, it rotates the plane of polarization. This property is called optical activity. A pair of enantiomers will rotate light to an equal degree but in opposite directions; one will rotate it clockwise (dextrorotatory), while the other will rotate it counterclockwise (levorotatory).

This distinct behavior is useful in many applications, especially in chemistry and biology, as it helps identify the specific configuration of molecules in complex systems.

Geometrical Isomerism

Geometrical isomerism, also referred to as cis-trans isomerism, arises due to restricted rotation around double bonds or within ring structures. Let's break down these terms for clarity.

* **Cis Isomers**: These occur when two substituent groups are on the same side of a double bond or a ring structure. * **Trans Isomers**: In trans isomers, the substituents are on opposite sides of the double bond or ring.
This kind of isomerism significantly affects the physical and chemical properties of compounds. For instance, the boiling and melting points can differ due to variations in molecular polarity and packing efficiency.
Geometrical isomers are particularly common in alkenes and cyclic compounds. They highlight the importance of spatial orientation in chemistry.

Enantiomers

Enantiomers are a special type of stereoisomer, often involved in optical isomerism. Chemically identical, they diverge in their spatial arrangement, forming non-superimposable mirror images. Enantiomers are crucial in demonstrating chirality, much like your left and right hands.

The intriguing part about enantiomers is their ability to affect biological systems differently. A small change in the orientation can lead to significant differences in biological activity and drug effectiveness. For example, one enantiomer of a drug might have beneficial effects, while its mirror image may be less effective or even harmful.
The concept of enantiomers underscores the importance of molecular orientation in the field of pharmaceuticals and beyond. Understanding how enantiomers work adds depth to the study of molecular interactions and their practical applications.