Question

Which of the following stereoisomers is a mirror image of itself? A. anomer B. epimer C. meso compound D. gcometric isomer

Short answer

C. meso compound

Step-by-step solution

Understand the Question

The question is asking which of the stereoisomers is a mirror image of itself. To answer this, you need to understand the properties of different stereoisomers.

Define Key Terms

1. **Anomer**: Anomers are a type of stereoisomer that differ in configuration only at the anomeric carbon. They are not necessarily mirror images of themselves.2. **Epimer**: Epimers differ in configuration at just one specific carbon atom among several chiral centers, and they are not mirror images of themselves.3. **Meso Compound**: Meso compounds are molecules with multiple chiral centers that have an internal plane of symmetry. This makes them superimposable on their mirror images, meaning they are mirror images of themselves.4. **Geometric Isomer**: Geometric isomers differ in the spatial arrangement across a double bond or rings, and are not generally mirror images of themselves.

Identify the Correct Option

Among the given options, a meso compound is the one that is a mirror image of itself due to the internal plane of symmetry.

Key concepts

Stereoisomers

Stereoisomers are molecules that have the same molecular formula and sequence of bonded atoms (constitution), but they differ in the three-dimensional orientations of their atoms in space. This characteristic can significantly influence the properties and reactions of the molecules.
There are several types of stereoisomers, including:

• Anomers: Differ only at the anomeric carbon in sugar molecules.
• Epimers: Differ at one specific carbon atom among several chiral centers.
• Meso Compounds: Have multiple chiral centers but also have an internal plane of symmetry, making them superimposable on their mirror images.
• Geometric Isomers: Differ in the spatial arrangement across a double bond or ring system, like cis and trans isomers.

Understanding these types helps in recognizing how molecules can have the same formula yet exhibit different properties.

Internal Plane of Symmetry

An internal plane of symmetry is a hypothetical line that divides a molecule into two mirror-image halves. This characteristic is crucial in identifying meso compounds.
For a molecule to have an internal plane of symmetry, it must be possible to imagine a plane cutting through the molecule such that one half is a mirror image of the other half. This feature makes the molecule achiral despite containing multiple chiral centers.
Consider a molecule with two chiral centers. Even if each chiral center could exist in two configurations (R or S), if the molecule can be divided into two mirror-image halves by an internal plane, it means:

• The molecule is superimposable on its mirror image.
• It doesn't exhibit optical activity because the effects of each chiral center cancel out.

This internal plane of symmetry is what makes meso compounds unique among stereoisomers.

Chiral Centers

A chiral center (or stereocenter) is an atom, most commonly a carbon atom, that has four different groups attached to it, leading to non-superimposable mirror images. A molecule with at least one chiral center can have isomers that are mirror images of each other, known as enantiomers.
Key points about chiral centers include:

• A molecule can have multiple chiral centers.
• Presence of chiral centers leads to stereoisomerism, where isomers have the same connectivity of atoms but differ in spatial arrangement.
• In the absence of an internal plane of symmetry, each chiral center contributes to the molecule's overall chirality.

However, if a molecule with multiple chiral centers has an internal plane of symmetry, it becomes a meso compound, making it achiral despite the presence of chiral centers.
Identifying chiral centers in a molecule is often the first step in determining the stereoisomeric relationships and properties of the molecule.