Problem 117 - A Complete Resource Book in Chemistry for JEE Main

Question

Consider the following statements about chirality: 1\. molecules which are not superimposable on their mirror images are achiral 2\. a chiral molecule can have simple axis of symmetry 3\. a carbon atom to which four different species are attached is a chiral centre. 4\. a compound whose molecules are achiral exhibits optical activity Which of the statements given above are correct? (a) 1,2 and 4 (b) 2,3 and 4 (c) 2 and 3 (d) 1 and 4

Step-by-Step Solution

Answer

Correct statement: 3. Closest correct option: (c).

Step 1: Analyze Statement 1

Statement 1 claims that molecules which are not superimposable on their mirror images are achiral. This is incorrect because being non-superimposable on a mirror image is a defining feature of **chiral** molecules, rather than achiral ones.

Step 2: Examine Statement 2

Statement 2 states that a chiral molecule can have a simple axis of symmetry. This statement is incorrect as chiral molecules lack such symmetry, meaning they cannot have any plane of symmetry or simple rotational symmetry.

Step 3: Evaluate Statement 3

Statement 3 indicates that a carbon atom with four different species attached is a chiral center. This is a correct statement because this arrangement creates a non-superimposable mirrored structure, making the carbon atom a chiral center.

Step 4: Consider Statement 4

Statement 4 claims that a compound with achiral molecules exhibits optical activity. This is false because compounds with achiral molecules do not show optical activity, as there is no asymmetry to cause the rotation of plane-polarized light.

Step 5: Determine Correct Statements

Based on our analysis, the only correct statement is Statement 3, identifying that a carbon atom with four different species is a chiral center. Statement 1, 2, and 4 are incorrect.

Step 6: Select the Correct Option

The only provided option containing Statement 3 only is (c), which states 2 and 3. Considering an error in all given options and typical occurrence of errors in problems, re-evaluation should point towards (c) as the closest option, assuming error in options.

Key Concepts

Chiral molecules

Chiral molecules have a unique characteristic where they cannot be superimposed on their mirror images. This means if you place a chiral molecule next to its mirror image, you will notice that they are not identical and cannot align perfectly, much like your left and right hand. This property distinguishes them from achiral molecules, which can be superimposed completely and appear identical to their mirror images.

Chirality is a fundamental concept in chemistry, especially in organic chemistry, as it plays a crucial role in how molecules interact with biological systems. For instance, many biological molecules are chiral, and this chirality can affect their function and interaction with other molecules.

Understanding chirality is essential for predicting the behavior and properties of molecules in chemical reactions and biological processes. This unique property also leads to the phenomenon of optical activity, linked directly to the chiral nature of molecules.

Chiral center

A chiral center is often defined by the presence of a carbon atom bonded to four different atoms or groups. This specific arrangement creates a non-superimposable structure, similar to how two hands cannot perfectly overlap. The carbon at the heart of this structure is referred to as a "chiral center" or "stereocenter."

This concept is crucial because the arrangement of atoms or groups around the chiral center determines the molecule's three-dimensional shape. This three-dimensionality is what causes such molecules to be involved in optical activity.

Recognizing chiral centers is an important skill in organic chemistry, enabling chemists to predict how molecules will behave in different environments, including biological systems. It's important to check for four different substituents when identifying potential chiral centers, as this is the classic signature of chirality.

Optical activity

Optical activity is a fascinating property exhibited by chiral substances. It occurs when a chiral molecule rotates the plane of polarized light passing through it. This rotation occurs because the asymmetrical structure of chiral molecules interacts differently with light depending on its direction.

The degree of rotation can vary based on factors such as the wavelength of the light and the specific arrangement of atoms within the chiral molecules. Importantly, this property is not observed in achiral substances, as they are symmetrical and do not interact with light in the same rotating way.

Determining optical activity is key in characterizing substances in chemistry, particularly with enantiomers—molecules that are mirror images of each other. These can have drastically different effects in biological contexts, so understanding their optical activity can be crucial in fields like pharmaceuticals and materials science. Enantiomers typically have different impacts due to their unique spatial arrangements, highlighting the importance of this characteristic in practical applications.