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Question: Find out the number of products of monochlorination of 2-methylbutane including stereoisomers.

The given answer is 6, but why can't it be 7? I am getting 7 products, the one which I am getting but not in the answer is given below:

enter image description here

Other 6 Product, enter image description here

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    $\begingroup$ Hard to tell what that diagram represents. It could be edited to show a clear diagram. See pubchem.ncbi.nlm.nih.gov//edit3/index.html for help. . For that matter, create th diagram there, and it can identify the name. $\endgroup$
    – DrMoishe Pippik
    Commented Mar 24 at 2:54
  • $\begingroup$ Thankyou for responding sir, I have changed the image $\endgroup$
    – Rudresh
    Commented Mar 24 at 3:09
  • $\begingroup$ OP, have they asked with stereoisomers / without stereoisomers? $\endgroup$
    – Harikrishnan M
    Commented Mar 24 at 3:10
  • $\begingroup$ Could you draw all the 7 isomers you obtained $\endgroup$
    – ananta
    Commented Mar 24 at 3:10
  • $\begingroup$ +1 for improving the diagram... but now you need to sow what the other 6 diagrams are. to see the difference. BTW, add all hydrogens, to show that all bonds are satisfied. $\endgroup$
    – DrMoishe Pippik
    Commented Mar 24 at 3:13

1 Answer 1

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Let us take the base compound, 2-methylbutane, as below.

enter image description here

I shall list down each compound, and explain my reasoning also.

This question is one of the more confusing ones as such, because people can easily leave out / count extra structures which might be same.

  1. 1-chloro-2-methylbutane

enter image description here

You must note that the below compound is also the same - the name will be the same.

enter image description here

Note that the 2nd carbon is chiral in nature (marked by the $\color{orange}{\text{orange letter A}}$) and hence we need to count this as 2 isomers - the d-isomer and the l-isomer.

  1. 2-chloro-2-methylbutane

enter image description here

Note that this is achiral and thus is counted as 1.

So, we've got 3.

  1. 2-chloro-3-methylbutane

enter image description here

Note that the carbon marked 'A' is chiral and thus, this isomer is counted as 2.

That makes it 5!

  1. 1-chloro-3-methylbutane: No chirality is present here, and thus it is counted as 1.

enter image description here

That makes it six, and we have come to the end of the list of monochloro derivatives from the reaction.

The reason why you might have got 7 is that (refer point 1) you have counted the 1st compound as 2, but in fact those 2 structures point to the same compound.

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  • $\begingroup$ To the downvoter: is there any way in which I can improve my answer? As far as I know I am sure that I am correct in my reasoning. $\endgroup$
    – Harikrishnan M
    Commented Mar 26 at 13:16

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