AIIMS 2006 Chemistry Diastereomers Assertion Reason Question

To tackle the question, we need to analyze both the assertion and the reason concerning diastereomers in stereochemistry.

Assertion: Diastereomers have different physical properties.

This statement is true. Diastereomers are stereoisomers that are not mirror images of each other and, importantly, they possess different physical and chemical properties. This distinction arises from their different spatial arrangements of atoms, which can lead to variations in boiling points, melting points, solubility, and reactivity.

Reason: They are non-superimposable mirror images.

This statement is false. The definition of non-superimposable mirror images applies to enantiomers, not diastereomers. Enantiomers are pairs of stereoisomers that are mirror images of each other and cannot be superimposed onto one another. On the other hand, diastereomers are not mirror images and can include compounds that have multiple stereocenters, leading to different configurations without the mirror image relationship.

Conclusion

Given that the assertion is true but the reason is false, the correct answer is:

C) Assertion is true but Reason is false.

Clarification of Other Options

• A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

  • This option is incorrect because the reason provided is false. While the assertion is true, the reason does not accurately explain it.

• B) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

  • This option is also incorrect because the reason is not true in the first place. Thus, both cannot be true.

• D) Both Assertion and Reason are false.

  • This option is incorrect as well, since the assertion is indeed true.

Additional Concepts

To further understand the properties of diastereomers, consider the following:

1. Physical Properties: Diastereomers may have significantly different boiling and melting points due to differences in intermolecular forces. For example, one diastereomer might form stronger hydrogen bonds than another.

2. Representation: Let's take an example of a compound with two stereocenters, such as 2,3-butanediol. The possible stereoisomers include:

   • (2R,3R)-2,3-butanediol
   • (2S,3S)-2,3-butanediol (enantiomer)
   • (2R,3S)-2,3-butanediol (diastereomer)
   • (2S,3R)-2,3-butanediol (diastereomer)

Both (2R,3S) and (2S,3R) are diastereomers of each other and have different physical properties, such as boiling points.

In summary, the assertion about diastereomers having different physical properties holds true, but the reasoning behind it is flawed because it confuses diastereomers with enantiomers. Understanding these distinctions is crucial in stereochemistry and can help in predicting the behavior of different compounds in chemical reactions.