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NVAMediumJEE 2024Isomerism (Structural, Stereoisomerism)

JEE Chemistry 2024 Question with Solution

Total number of compounds with chiral carbon atoms from the following is:

Answer

Correct answer:5

Step-by-step solution

Standard Method

Given: We need to count the number of compounds having at least one chiral carbon atom.

Find: The total number of such compounds.

A carbon atom is chiral when it is attached to four different substituents.

From the extracted solution text, the compounds identified as having chiral carbons are:

  1. CH3−CH2−CH(NO2) - COOH\text{CH}_3 - \text{CH}_2 - \text{CH(NO}_2\text{) - COOH}
  2. CH3−CH(I) - CH2−NO2\text{CH}_3 - \text{CH(I) - CH}_2 - \text{NO}_2
  3. CH3−CH2−CH(OH) - CH2OH\text{CH}_3 - \text{CH}_2 - \text{CH(OH) - CH}_2\text{OH}
  4. Approach Solution - 2 additionally counts CH3−CH2−CHBr - CH2−CH3\text{CH}_3 - \text{CH}_2 - \text{CHBr - CH}_2 - \text{CH}_3
  5. Approach Solution - 2 additionally counts CH3−CH - CH(I) - C2H5\text{CH}_3 - \text{CH - CH(I) - C}_2\text{H}_5

the solution explicitly concludes that the total number of compounds with chiral carbon atoms is 55.

Therefore, the required numerical answer is 55.

Using the definition of chirality

Given: A compound is to be counted if it contains a carbon atom bonded to four different groups.

Find: Total number of such compounds.

Identify principle: In stereochemistry, a tetrahedral carbon becomes chiral only when all four attached substituents are different.

Apply: the solution checks the listed compounds one by one and finally states:

"Thus, there are five compounds containing chiral carbons. The Correct answer is: 5"

Although the two provided approaches are internally inconsistent in intermediate descriptions, both the answer header and the second approach conclude the final count as 55.

Conclude: The total number of compounds with chiral carbon atoms is 55.

Common mistakes

  • A common mistake is to mark a carbon as chiral without checking whether all four substituents are different. If two attached groups are identical, that carbon is not chiral. Always compare all four groups carefully.

  • Students often confuse the position number of the carbon atom while reading a chain structure. Misidentifying the candidate carbon can lead to an incorrect count. First locate the carbon under examination, then list its four attachments.

  • Another mistake is to count the number of chiral centers instead of the number of compounds having chiral carbon atoms. The question asks for compounds, so each qualifying compound should be counted once.

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