Question

Which will exhibit geometrical isomerism here? (a) \(\mathrm{A}_{2} \mathrm{C}=\mathrm{CAB}\) (b) \(\mathrm{A}_{2} \mathrm{C}=\mathrm{CB}_{2}\) (c) \(\mathrm{ABC}=\mathrm{CAB}\) (d) \(\mathrm{ABC}=\mathrm{CX}_{2}\)

Short answer

Option (d) ABC = CX_{2} can exhibit geometrical isomerism.

Step-by-step solution

Understand Geometrical Isomerism

Geometrical isomerism occurs in compounds with restricted rotation around a bond, usually a double bond, and the presence of different groups around the atoms involved in the bond. In simpler terms, the molecule must have non-identical groups attached to the atoms of a double bond.

Analyze Option (a)

The compound _{2} C= CAB includes two identical A groups attached to the same carbon, which means it cannot show geometrical isomerism as we need different groups attached to one end of the double bond.

Analyze Option (b)

The compound _{2} C= CB_{2} includes two identical A groups attached to one carbon and two identical B groups attached to the other carbon of the double bond, hence no different groups presented. Therefore, it cannot exhibit geometrical isomerism.

Analyze Option (c)

In ABC = CAB, we have three different groups A, B, and C on both sides of the double bond, but due to identical arrangement on both sides, it is unlikely to exhibit geometrical isomerism here as well.

Analyze Option (d)

The compound ABC = CX_{2} has one side with different groups (A, B, C) and the other side with two identical X groups attached to the carbon. With different substituents possible at one end and identical ones at the other, there's a potential for restricted rotation leading to geometrical isomerism.

Key concepts

Organic Chemistry

Organic chemistry is a branch of chemistry that deals with compounds primarily composed of carbon, hydrogen, and often other elements like oxygen, nitrogen, sulfur, and halogens. It involves understanding the structure, composition, reactions, and properties of organic compounds. One fascinating phenomenon in organic chemistry is isomerism, particularly geometrical isomerism. Geometrical isomers are a type of stereoisomer where the arrangement of atoms differs around a double bond, resulting in compounds with distinct properties.

In organic molecules, the presence of a carbon-carbon double bond generally restricts free rotation due to its rigid nature. This restricted rotation can lead to the formation of different spatial arrangements of atoms, known as cis-trans isomerism, which is a subset of geometrical isomerism.

Isomers

Isomers are compounds that share the same molecular formula but differ in structural or spatial arrangement. This diversity in arrangement can lead to significant differences in chemical and physical properties.

• Structural isomers: They differ in the covalent arrangements of atoms.
• Stereoisomers: These isomers have the same structural formula and sequence of bonded atoms, but they differ in the 3D positioning of the atoms.

Geometrical isomerism is a type of stereoisomerism where we see a variation in the spatial arrangement due to restricted rotation around a double bond.

In exploring geometrical isomerism, it is crucial to remember that different substituents are necessary around the double-bonded carbon atoms. Without this, isomerism cannot be exhibited since no variation in spatial arrangement would be present.

Double Bond Rotation

In molecules, single bonds allow free rotation of atoms attached to the carbon atoms. However, a double bond between carbon atoms presents a different scenario due to the pi bond, which locks the atoms in place and restricts rotation.

This restriction leads to different spatial arrangements of the substituents, giving rise to geometrical isomerism.

Here’s why it matters:

• Different spatial arrangements can result in distinct physical properties, like melting and boiling points.
• They might react differently under the same conditions due to their spatial configuration.

Geometrical isomers are often labeled as 'cis' or 'trans' based on the relative positions of initially identical groups or atoms on the same or opposite sides of the double bond. This distinction highlights the importance of the restricted rotation in defining the properties and reactivity of a molecule.

Identical Groups

The existence of identical groups plays a crucial role in determining whether a compound can exhibit geometrical isomerism. For a compound to potentially form such isomers, each of the carbon atoms involved in the double bond must have different groups attached to it.

When identical groups are attached to a carbon in a double-bond scenario, it essentially negates the possibility of forming different spatial arrangements required for geometrical isomerism. This is because:

• Having identical groups means there’s no variation in arrangements since identical groups provide no change in spatial positioning.
• The unique properties that arise due to different spatial arrangements won't occur.

Thus, for a molecule to show geometrical isomerism, each of the involved carbon atoms should ideally bond with a variety of different substituents, eliminating identical groups on the same side, thus allowing for the possibility of a 'cis' or 'trans' distinction.