Question

A molecule is said to be chiral only if (1) it is superimposable on its mirror image. (2) it is nonsuperimposable on its mirror image. (3) it possess stereogenic centres. (4) it can have different configurations.

Short answer

Option 2: A molecule is chiral if it is non-superimposable on its mirror image.

Step-by-step solution

Understand the Definition of Chirality

Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image. This means the molecule and its mirror image are not the same, similar to how left and right hands are related.

Analyze Each Option

Review each option to determine if they align with the definition of chirality.

Option 1 Analysis

Option 1 states that a molecule is chiral if it is superimposable on its mirror image. This contradicts the definition of chirality, so it is incorrect.

Option 2 Analysis

Option 2 states that a molecule is chiral if it is non-superimposable on its mirror image. This aligns with the definition of chirality, so it is correct.

Option 3 Analysis

Option 3 mentions that a molecule is chiral if it possesses stereogenic centres. While many chiral molecules do have such centers, it is not a definitive condition for chirality. Some molecules with stereogenic centers can be superimposable on their mirror images.

Option 4 Analysis

Option 4 states that a molecule is chiral if it can have different configurations. Molecules can have different configurations without being chiral, so this option is not always true.

Conclusion

Based on the analysis, option 2 is the correct description of chirality.

Key concepts

non-superimposable mirror images

A key concept in chirality is the idea of non-superimposable mirror images. This just means that a molecule and its mirror image cannot be perfectly aligned with one another. Imagine your hands. When you place your left hand over your right hand, they don't match up perfectly.

Similarly, chiral molecules have this property. Their mirror images are not identical, even though they look similar. This is crucial for many biological compounds, as the shape and orientation can affect how they interact with other molecules in the body. By recognizing whether a given molecule and its mirror image are non-superimposable, you can determine if the molecule is chiral.

stereogenic centers

Stereogenic centers, also known as chiral centers, play a significant role in determining the chirality of a molecule. A stereogenic center is usually a carbon atom bonded to four different groups. This configuration creates different spatial arrangements, which leads to different mirror images.

It's important to note that while many chiral molecules have stereogenic centers, this alone doesn't always guarantee chirality. There are cases where molecules might have stereogenic centers but are still superimposable with their mirror images, meaning they are not chiral. Therefore, identifying stereogenic centers is a good starting point but may require further analysis to confirm chirality.

molecular configurations

Molecular configurations refer to the spatial arrangement of atoms in a molecule. Chirality is significantly influenced by these configurations. If you can arrange atoms in a way that produces different mirror images that are non-superimposable, you have identified a chiral molecule.

There are multiple ways molecules can be arranged, which results in different configurations. For a molecule to be chiral, altering its configuration should result in non-superimposable mirror images. This distinct arrangement affects how molecules function and interact, especially in biological systems. Understanding molecular configurations is crucial in the study of chirality and its implications in various scientific fields.