Question

A chiral molecule has (a) no plane of symmetry (b) one plane of symmetry (c) infinite planes of symmetry (d) none of these

Short answer

The correct answer is (a) no plane of symmetry.

Step-by-step solution

Definition of Chirality

Chirality is a property of a molecule that occurs when it cannot be superimposed onto its mirror image. The presence or absence of a plane of symmetry can be used to determine whether a molecule is chiral or not.

Plane of Symmetry in Chiral Molecules

A plane of symmetry in a molecule, also called a mirror plane, is a hypothetical plane that cuts the molecule into two halves - each being a mirror image of the other. Chiral molecules do not possess a plane of symmetry as they cannot be split into two mirror-image halves.

Selecting the Correct Option

Given the earlier definitions and explanations, we know that a chiral molecule will have no plane of symmetry. Therefore, the correct choice from the given options is (a) no plane of symmetry.

Key concepts

Plane of Symmetry

A plane of symmetry, sometimes referred to as a mirror plane, is a critical concept in understanding molecular structures. It is an imaginary plane that divides a molecule into two mirror-image halves.
This can be a useful way to assess whether a molecule has symmetrical properties. If such a plane exists within a molecule, each half is the mirror reflection of the other. This symmetry often reflects on the molecule’s physical and chemical properties.

• In symmetrical molecules, there is at least one plane of symmetry.
• These molecules tend to be achiral, indicating they are superimposable on their mirror image.

Since chiral molecules lack a plane of symmetry, this means they are structurally unique on one side compared to the other when evaluated across this hypothetical plane.

Chiral Molecules

Chiral molecules are an intriguing group of compounds in chemistry defined by their lack of superimposability upon their mirror images. This inability to be superimposed stems from the molecule's asymmetry. Essentially, it does not have an internal plane that splits it into mirrored portions.
The ideal way to think of chirality is like comparing your left and right hands. While they are similar, they are not identical and cannot be aligned perfectly when overlaid.

• Chiral molecules typically possess a carbon atom bonded to four different groups, known as a stereocenter or chiral center.
• The unique 3D arrangement is what renders them non-superimposable on their mirror images.

It's these properties that make chiral molecules crucial in fields like pharmacology, where they can have different biological functions depending on their orientation.

Mirror Image

A mirror image is the reflection that is seen when an object is mirrored along a plane.
In chemistry, particularly when studying molecules, the mirror image concept helps in identifying the chirality of a molecule. If a molecule and its mirror image cannot be superimposed, it suggests a chiral nature.

• Identities like hands and feet are classic examples, which display chirality as each is a mirror image yet cannot be mapped directly on each other.
• In the context of molecules, being able to or failing to align the mirror image directly reflects whether a molecule possesses chirality.

Understanding mirror images in chemical structures aids in grasping the difference between chiral and achiral molecules, each holding significant implications in molecular science.