Permutations in Organic Chemistry

Chemistry Level 3

Consider the compound C ( C H ( C H X 3 ) C l ) X 4 \ce{C(CH(CH3)Cl)4 }

Let A A denote the number of Stereoisomers for the above compound.
Let B B denote the number of Meso compounds in the above list.

Find A + B A+B .


The answer is 6.

Aniswar S K by Aniswar S K , 20, India

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1 solution

Aniswar S K
Apr 1, 2017

This is mathematically equivalent to this problem. There are four coins arranged in a circular fashion. each coin can show either a head or a tail. Find the number of arragnements.

Here the coins are the 4 carbons adjacent to the central carbon, and heads and tails are their configurations( R or S).

The possibilities are

  1. RRRS Why i am saying this is related to circular permutation is that in a tetrahedron in doesnt matter whether you have RRRS or SRRR or RSRR,etc.

  2. RRRR

  3. RRSS Note that this is the meso compound. Its mirror image will be SSRR which is same as RRSS as you can rotate the tetrahedron and superimpose them.

  4. SSSS (Mirror image of RRRR - enantiomer)

  5. SSSR (Mirror image of RRRS - enantiomer)

Therefore A=5, B=1

Hence A+B =6

Hope I have made myself clear!!

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