Problem 169 - A Complete Resource Book in Chemistry for JEE Main

Question

A similarly 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

Step-by-Step Solution

Answer

(c) Both are included in stereoisomerism.

Step 1: Understand the Problem

We need to determine the similarity between optical isomerism and geometrical isomerism by analyzing the given options.

Step 2: Analyze Option (a)

Option (a) states that if one type of isomerism is present, then so is the other. This isn't true because a compound can exhibit only one type of isomerism independently.

Step 3: Analyze Option (b)

Option (b) suggests that both types of isomerism form an equal number of isomers for a given compound. However, the number of isomers depends on the specific structural arrangement, not on the type of isomerism.

Step 4: Analyze Option (c)

Option (c) states that both optical and geometrical isomerism are included in stereoisomerism. This is accurate, as both involve different spatial arrangements of atoms.

Step 5: Analyze Option (d)

Option (d) claims that optical and geometrical isomerism have no similarity, which is incorrect because both are types of stereoisomerism.

Step 6: Select the Correct Answer

Given the analysis, the correct similarity between optical and geometrical isomerism is that both are forms of stereoisomerism, making option (c) the correct choice.

Key Concepts

Optical Isomerism

Optical isomerism is a type of stereoisomerism where molecules have the same molecular formula and sequence of bonded atoms, but they differ in how they affect plane-polarized light. These isomers, known as enantiomers, are mirror images of each other and cannot be superimposed on one another, much like how your right and left hands are mirror images but not identical. This property is crucial in fields like pharmacology, as different enantiomers of a medication may have different effects on the body.

Enantiomers are typically identified using a polarimeter. When plane-polarized light passes through a solution of one enantiomer, it will rotate the plane of that light to the right (dextrorotatory "D"), or to the left (levorotatory "L"). A racemic mixture contains equal amounts of both enantiomers, leading to no net rotation of polarized light.

Optical isomerism is often found in compounds with chiral centers. A chiral center typically has four different groups attached, leading to multiple spatial arrangements.

Geometrical Isomerism

Geometrical isomerism, also known as cis-trans isomerism, occurs in compounds that have restricted rotation around a bond, usually a carbon-carbon double bond or a ring structure. This type of isomerism arises due to the arrangements of groups around a bond or a structure, leading to different spatial distribution.

The most common type of geometrical isomerism involves two substituents, which can either be on the same side (cis) or on opposite sides (trans) of the double bond or the ring. These variations in arrangement influence the physical and chemical properties of the molecules. For example, cis isomers generally have higher boiling points than trans isomers due to polar intermolecular forces.

Geometrical isomers often exhibit differing reactivity and biological activity, making them significant in chemical synthesis and pharmaceuticals. Unlike optical isomers, geometrical isomers don't necessarily involve a chiral center since it is the restricted rotation that causes the differences.

Spatial Arrangements of Atoms

The concept of spatial arrangements of atoms lies at the heart of stereoisomerism, which encompasses both optical and geometrical isomerism. Stereoisomerism involves isomers with the same structural formulas but different three-dimensional configurations, significantly impacting their physical, chemical, and biological properties.

• Optical isomers arise from different arrangements around a chiral center.
• Geometrical isomers result from different spatial placements around a double bond or in a ring.

The study of these spatial arrangements is essential in understanding how molecules interact with each other and with the environment. Such understanding is crucial in drug design, where the spatial arrangement can determine the efficiency and interaction of a drug with its target.

In stereochemistry, spatial arrangement analysis helps in predicting the behavior of molecules in different environments, such as reactions involving catalysts, which might favor one isomeric form over another. This highlights why the study and analysis of spatial arrangements of atoms are pivotal for chemists working in synthesis, materials science, and biochemistry.