Question

\(A\) similarity betwecn optical and geometrical isomcrisms is that \(\quad\) (AIEEE 2002) (1) cach forms cqual number of isomers for a given compound. (2) if in compound, one is present then so is the other. (3) both are included in stercoisomerism. (4) they have no similarity.

Short answer

Option (3): both are included in stereoisomerism.

Step-by-step solution

Understand the Problem

The question asks to identify a similarity between optical and geometrical isomers given four options.

Review Definitions

Optical isomers are molecules that differ in the way they rotate plane-polarized light. Geometrical isomers, also known as cis-trans isomers, occur due to the restricted rotation around a double bond or a ring structure.

Analyze Each Option

Evaluate each option to determine if it describes a similarity between optical and geometrical isomers.

Option (1)

Each type of isomer (optical or geometrical) does not necessarily form the same number of isomers for a given compound. This option is incorrect.

Option (2)

Optical and geometrical isomers can exist independently. The presence of one does not guarantee the presence of the other. This option is incorrect.

Option (3)

Both optical and geometrical isomers fall under the category of stereoisomerism, which involves isomers that have the same connectivity but differ in spatial arrangement. This option is correct.

Option (4)

Option (4) states that they have no similarity, which we already know is incorrect because option (3) is correct.

Choose the Correct Answer

After evaluating all options, the correct similarity between optical and geometrical isomers is given by option (3): both are included in stereoisomerism.

Key concepts

Optical Isomers

Optical isomers are a fascinating type of stereoisomers. These isomers differ based on their interaction with plane-polarized light. When a compound can rotate plane-polarized light, it's known as optically active.
There are two primary types of optical isomers: enantiomers and diastereomers. Enantiomers are mirror images of each other but cannot be superimposed, much like our left and right hands. Diastereomers, on the other hand, are not mirror images of each other.
Optical isomerism arises due to the presence of chiral centers (usually carbon atoms bound to four different groups). The key characteristics of optical isomers are:

• They rotate plane-polarized light.
• Enantiomers rotate light to equal degrees but in opposite directions (one to the left and the other to the right).
• They have identical physical properties except for their interaction with polarized light and reactions with other chiral molecules.

Geometrical Isomers

Geometrical (cis-trans) isomers are another type of stereoisomer, but they differ from optical isomers in their formation. Geometrical isomerism occurs due to restricted rotation, typically around a double bond or within a ring structure.
The two main forms of geometrical isomers are:

• **Cis isomers**: Groups are on the same side of the double bond or ring.
• **Trans isomers**: Groups are on opposite sides.

Geometrical isomers have distinct physical and chemical properties. For example, cis isomers may have a higher boiling point than their trans counterparts, due to stronger intermolecular forces.
Characteristics of geometrical isomers include:

• Different physical properties like melting points and solubilities.
• Different chemical reactivities.
• Both exist due to the rigidity in their structure, preventing rotation.

AIEEE Chemistry

AIEEE (All India Engineering Entrance Examination) chemistry covers a broad range of topics, including stereoisomerism. Understanding stereoisomers is crucial for students appearing for this competitive exam, as it is a common subject in many questions.
In the context of AIEEE, students should be able to:

• Identify and differentiate between optical and geometrical isomers.
• Understand the conditions under which each type of isomerism occurs.
• Apply this knowledge to solve related multiple-choice questions confidently.

The similarity between optical and geometrical isomers, which is often tested, is that both fall under the umbrella of stereoisomerism. This involves isomers with the same molecular formula and connectivity but differing in spatial arrangement.
AIEEE helps build a strong foundational understanding of such concepts, ensuring students are well-prepared for higher education in engineering and related fields.