Question

The necessary condition for a compound to be optically active is (a) the presence of no chiral atom (b) the presence of atleast one asymmetric atoms (c) the presence of chirality in the molecule (d) none of these

Short answer

The necessary condition for a compound to be optically active is the presence of at least one asymmetric atoms (Option b).

Step-by-step solution

Understanding Chirality

Optical activity in compound spotlights on chirality of molecules. Chirality refers to the existence of two mirror-image forms of a molecule, termed enantiomers. These molecules are non-superimposable on their mirror images.

Chiral Atom Definition

A chiral atom, or asymmetric atom, is an atom that has different substituents attached to it. This creates a situation where there's no symmetry in the molecule.

Determining the Condition for Optical Activity

Given the understanding of chirality and chiral atoms, it can be stated that for a compound to exhibit optical activity, there must be at least one chiral or asymmetric atom present in the molecule. This statement aligns with option (b).

Key concepts

Optical Activity

Optical activity is a fascinating property of certain molecules that allows them to rotate plane-polarized light. This phenomenon occurs due to the presence of chirality in the molecule, meaning that the molecule has a non-superimposable mirror image. Imagine your left and right hand, which are mirror images but cannot be perfectly aligned atop one another; this is a helpful way to understand chirality. When light passes through a chiral molecule, the direction of its polarization can change. This deviation in light is what we observe as optical activity.

In the world of chemistry, detecting and measuring optical activity is crucial. It helps chemists understand the structure of a molecule. Moreover, optical activity reveals information about the specific arrangement of atoms within chiral compounds. This property is not only essential in fundamental chemistry but also in fields that study biological activities, such as biochemistry, where many biomolecules are chiral.

Chiral Atom

A chiral atom, often called an asymmetric atom, is the central concept in understanding molecular chirality. This is most commonly a carbon atom bonded to four distinct substituents. When a molecule has at least one carbon atom with four different groups attached, it becomes chiral. Because of this configuration, the molecule lacks symmetry and will be optically active, displaying two non-superimposable mirror images known as enantiomers.

Chiral atoms play a significant role in defining how molecules interact with other molecules. For instance, they will interact differently with biological systems, which are themselves often chiral. This interaction specificity is the foundation of many pharmaceutical effects, where one enantiomer of a drug may be beneficial, while the other could be harmful or inactive. Identifying chiral atoms is therefore a critical step in chemistry and related fields.

Asymmetric Molecule

An asymmetric molecule is one that does not have an internal plane of symmetry, typically due to the presence of one or more chiral atoms. This lack of symmetry leads to the molecule's ability to rotate plane-polarized light, hence displaying optical activity.

Structure can vary widely, making each asymmetric molecule unique in shape and behavior. Such molecules often possess unique physical and chemical properties compared to their symmetric counterparts.

The asymmetry in these molecules allows chemists to find different molecular behaviors and interactions. Many natural substances and commercial products are comprised of asymmetric molecules. Their distinct interactions are what give rise to diverse and intricate properties that are explored in numerous scientific and industrial applications.