Question

\(\Lambda\) compound whosc molccules arc superimposable on their mirror images even though they contain asymmetric carbon atom is called (Kerala MEE 2003) (1) a meso compound. (2) an erythro isomer. (3) a threo isomer. (4) a glycol. (5) an electric compound.

Short answer

1) a meso compound.

Step-by-step solution

Identify the Asymmetric Carbon

An asymmetric carbon atom (or chiral carbon) is a carbon atom that is attached to four different groups. This concept is crucial for understanding chirality and superimposability.

Understand Superimposability

If a molecule is superimposable on its mirror image, it means that the two structures are identical and do not exhibit chirality.

Define Meso Compounds

Meso compounds are stereoisomers that contain multiple chiral centers but are superimposable on their mirror images due to an internal plane of symmetry.

Compare with Given Options

Given the information, the compound must be meso if it is superimposable on its mirror image despite having asymmetric carbon atoms. Other options do not fit this description.

Key concepts

Asymmetric Carbon

An asymmetric carbon, also known as a chiral carbon, is a carbon atom bonded to four different groups.
This unique configuration is essential for the molecule's three-dimensional structure.
Because it has four distinct attachments, the arrangements of these groups can vary, creating molecules that are not identical. An easy way to recognize an asymmetric carbon is to look at each carbon atom in the molecule and check if it has four different groups attached.
For example, in organic compounds like amino acids or sugars, you will often find asymmetric carbons.

This carbon atom forms the basis for the molecule's chirality.

Chirality

Chirality is a property of a molecule that arises when a molecule cannot be superimposed on its mirror image.
This means that the molecule and its mirror image are different - much like our left and right hands. Molecules with chiral centers (chiral carbons) exhibit this property. If a molecule has one or more asymmetric carbon atoms, it usually shows chirality.
This has significant implications in chemistry and biology because chiral molecules can behave differently in biological systems.

Chirality is crucial in pharmaceuticals, as the two mirror images, called enantiomers, can have different effects on the body.

• One enantiomer of a drug might be therapeutic,
• while the other could be inactive or even harmful.

Superimposability

Superimposability means that when you place one object over its mirror image, they match up perfectly.
For molecules, if you can superimpose a molecule on its mirror image, it means they are identical. Not all molecules can be superimposed on their mirror images.
Those that can be are not chiral. Meso compounds are a special case in this context.
They have multiple asymmetric carbons but are still superimposable on their mirror images due to an internal plane of symmetry.

This means that even with chiral centers, meso compounds are not chiral overall.