Question

The compound which can show both optical and geometrical isomerism is (A) Polythene (B) Chloroprene (C) Nylon-6,6 (D) Buna-S

Short answer

The compound that can exhibit both optical and geometrical isomerism is (B) Chloroprene. It has a chiral carbon bonded to four different groups and a restricted double bond, allowing it to exhibit both types of isomerism.

Step-by-step solution

Understand Optical Isomerism Conditions

Optical isomerism occurs when a compound has a chiral center, which is an atom (usually carbon) bonded to four different groups. These compounds are non-superimposable mirror images of each other and they can rotate plane-polarized light in different directions. #define geometrical isomerism conditions#

Understand Geometrical Isomerism Conditions

Geometrical isomerism occurs when a compound has a restricted rotation around a double bond or ring structure, causing different spatial arrangements of its substituent groups. These different arrangements are called cis and trans isomers. #Step 1: Analyze the structure of each compound# #A - Polythene#

Examine Polythene

Polythene is a polymer made from the repetition of ethylene units. It does not have a chiral center or a double bond, which means it cannot exhibit optical or geometrical isomerism. #B - Chloroprene#

Examine Chloroprene

Chloroprene is a monomer with the molecular formula C4H5Cl. It has a chiral carbon bonded to four different groups and has a restricted double bond. Therefore, it can exhibit both optical and geometrical isomerism. #C - Nylon-6,6#

Examine Nylon-6,6

Nylon-6,6 is a synthetic polymer made from the condensation reaction between hexamethylenediamine and adipic acid. It does not have any chiral centers or restricted bonds. Therefore, it cannot exhibit optical or geometrical isomerism. #D - Buna-S#

Examine Buna-S

Buna-S, also known as Styrene-butadiene rubber, is a polymer composed of repeating styrene and butadiene units. It does not have any chiral centers. However, it contains restricted double bonds in the butadiene units. It can exhibit geometrical isomerism but not optical isomerism. #Step 2: Identify the compound with both optical and geometrical isomerism#

Identify the Correct Compound

Based on the analysis, only chloroprene (B) can exhibit both optical and geometrical isomerism. The other compounds either do not exhibit isomerism or exhibit only one type of isomerism. Therefore, the correct answer is (B) Chloroprene.

Key concepts

Optical Isomerism

Optical isomerism is a fascinating concept in chemistry where certain compounds have the ability to rotate plane-polarized light. This phenomenon occurs due to the presence of a chiral center within the molecule. A chiral center, often referred to as a stereocenter, is typically a carbon atom that is attached to four different atoms or groups.

A major characteristic of compounds exhibiting optical isomerism is that they have non-superimposable mirror images known as enantiomers. Enantiomers can have significantly different behaviors, especially in biological systems. For instance, one enantiomer of a compound may be therapeutically active, while its mirror image might be inactive or even harmful.

Recognizing optical isomerism in compounds involves identifying the chiral center and confirming that it leads to non-superimposable mirror images. A simple yet exciting demonstration of optical activity is the ability of these isomers to rotate light in different directions, either to the right (dextrorotatory) or to the left (levorotatory).

Geometrical Isomerism

Geometrical isomerism, also known as cis-trans isomerism, arises from the restricted rotation around a double bond or within ring structures. This restriction keeps certain substituents on the same side or opposite sides of the bond, resulting in different spatial arrangements of the atoms.

The classic example used to explain geometrical isomerism is the case of alkenes, where substituents can be positioned either as cis (same side) or trans (opposite sides) with respect to the double bond. Such differences in spatial arrangement can lead to distinct physical and chemical properties between the isomers, although the chemical formula remains unchanged.

It's important to note that not all double-bonded compounds can show geometrical isomerism. For instance, when two substituents on the same carbon atom are identical, geometrical isomerism cannot occur. Understanding this is key to identifying compounds like chloroprene, which can show variations in geometrical arrangements due to its molecular structure.

Chirality

Chirality is a geometric property that is common in organic molecules, significantly affecting their chemical and physical properties. A chiral molecule is one that cannot be superimposed on its mirror image, much like how our left and right hands are mirror images but not identical.

In chemistry, chirality is crucial for understanding reaction mechanisms and properties of molecules. The presence of a chiral center, often a carbon atom attached to four different groups, gives rise to this property. This results in the existence of enantiomers, which are pairs of chiral molecules that display optical activity.

Chirality is especially important in fields such as pharmaceuticals, where different enantiomers of a drug can have dramatically different effects on the body. Identifying and understanding chirality in compounds helps chemists to predict and explain the behavior of molecules, such as why chloroprene exhibits both optical and geometrical isomerism due to its chiral centers and structural properties.