Stereochemistry Quiz: Test Your Knowledge

The molecule shown is achiral because it has a plane of symmetry. Here’s a breakdown:



Symmetry: The cyclobutane ring has two hydroxyl groups (-OH) attached at equivalent positions. If you imagine cutting the molecule vertically down the middle, the two halves are mirror images of each other.



Superimposability: For a molecule to be chiral, it must lack internal symmetry, and its mirror image must not be superimposable on the original. In this case, since the molecule can be divided into two identical halves, it is superimposable on its mirror image.



Therefore, the presence of this internal plane of symmetry makes the molecule achiral.

This molecule is chiral.

Here's why:

• Chiral Center: The central carbon atom is attached to four different groups:
  
  
  
  • -CH₂OH
  
  
  • -CO₂H
  
  
  • -CO₂H
  
  
  • -H
  • 
    
  
  
  
  


• No Plane of Symmetry: You cannot draw any plane through this molecule that would create mirror image halves.
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Important Note: Even though there are two -CO₂H groups, their spatial arrangement around the central carbon makes them distinct in this 3D structure. This lack of symmetry is what makes the molecule chiral.

The molecule shown is achiral. Here's why:

• Double bond constraint: The molecule has a double bond between two carbon atoms, which restricts rotation around the bond. The two hydrogens attached to the leftmost carbon are identical.

  
  

• Symmetry: For chirality, the carbon at the stereocenter (the carbon attached to four different groups) must have four distinct substituents. In this case, the left side of the molecule has two identical hydrogen atoms attached to the same carbon, making it symmetric.

  
  

Since the molecule has symmetry and lacks four distinct groups around the potential stereocenter, it is achiral. 

The compound contains five asymmetric carbons. Here's the reasoning:

Definition of an asymmetric carbon: An asymmetric carbon, or chiral carbon, is defined as a carbon atom attached to four distinct groups. To determine the number of asymmetric carbons, one must carefully analyze each carbon in the molecule to check if it connects to four different substituents.

In this compound, all five carbon atoms in the main chain meet this criterion, as each one is attached to four different groups. Hence, the total number of asymmetric carbons is confirmed to be 5.

There is only one asymmetric carbon in the compound. Here's why:

Definition of an asymmetric carbon: An asymmetric carbon, or chiral carbon, is a carbon atom bonded to four distinct groups, leading to chirality. To identify asymmetric carbons, one must examine each carbon in the structure and determine if it is attached to four different substituents.

Analysis of the compound: In this particular compound, careful examination reveals that only one carbon fulfills this requirement. Therefore, it is classified as the only asymmetric carbon, confirming the answer as 1.

The molecule shown is chiral. Here's why:

Definition of chirality: A chiral molecule cannot be superimposed on its mirror image, meaning it has a unique three-dimensional structure. This distinctiveness arises when a carbon atom is bonded to four different substituents, creating a stereocenter.

Lack of symmetry: In chiral molecules, no plane of symmetry exists that divides the molecule into two identical halves. In this case, the arrangement of the substituents creates an asymmetrical shape, confirming that it is chiral.

Thus, due to the presence of a stereocenter and the absence of symmetry, the molecule is classified as chiral.

There are no enantiomers of the molecule shown. Here's why:

Lack of chiral centers: For a molecule to have enantiomers, it must contain at least one chiral center (a carbon atom bonded to four different groups). In the molecule provided, there are no such asymmetric carbons.

Symmetry: The molecule likely has a plane of symmetry or some form of internal symmetry, which makes it achiral. Symmetrical molecules do not have non-superimposable mirror images.

Since the molecule lacks chiral centers and has symmetry, it does not have any enantiomers, making the correct answer 0.

The pair of compounds shown are enantiomers. Here's why:

Non-superimposable mirror images: The two compounds are mirror images of each other, but they cannot be superimposed. This is the defining characteristic of enantiomers.

Stereocenters: Each compound contains one or more stereocenters (chiral carbons), with the spatial arrangement of groups around these centers being opposite in each molecule.

Same connectivity, different spatial arrangement: Both compounds have the same molecular connectivity but differ in the three-dimensional arrangement of their atoms.

Since they are non-superimposable mirror images with chiral centers, the pair of compounds are classified as enantiomers.