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How many products can we get from the monochlorination of 2,4-dimethylpentane including stereoisomerism? I have seen someone say that it yields 3 structural isomers one of which has two enantiomers making them 4 products in total, but I couldn't find the chiral carbon he was talking about.

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  • $\begingroup$ Monochlorination of 2,4-dimethylpentane can yield 4 structural isomers. None of those isomers have chiral carbon atoms. $\endgroup$ – Fabio Jul 7 at 20:53
  • $\begingroup$ It certainly doesn't yield 4 structural isomers according to my college professor and to this guy on Quora, they both say it yields 3 structural isomers yet the dispute between the two is that of one of those 3 structural isomers has an enantiomer which makes the total 4. quora.com/… $\endgroup$ – ALPHAz CoC Jul 7 at 21:10
  • $\begingroup$ The term "products" is vague. Constitutional (structural) isomers have the same molecular formula but different atom connectivities. In your example, there are three structural isomers. Stereoisomers have the same molecular formula, the same atom connectivity but different arrangements in space. Thus, the enantiomers of 1-chloro-2,4-dimethylpentane are stereoisomers of each other. Constitutional isomers are a subset of isomers (same molecular formula) and stereoisomers are a subset of constitutional isomers. $\endgroup$ – user55119 Jul 7 at 23:44
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The expected products of mono-chlorination of 2,4-dimethylpentane are depicted in following scheme:

Monochlorination

The substrate has 12 primary hydrogens (on 1-,1'-, 5-, and 5'-methyl groups), 2 secondary hydrogens (on 3-methylene group), and 2 tertiary hydrogens (on 2-, and 4-methine groups), as numbered in the scheme. Altogether, total of 3 different hydrogens are present, therefore, 3 different mono-chlorinated products are possible as sketched in the bottom boxes of the scheme. Although 1- and 1'-methyl groups (and 5- and 5'-methyl groups as well) are equivalent in the structure, mono-chlorination of each would give different stereoisomer (strictly speaking, enentiomers). Therefore, counting stereoisomers, you should get total of 4 different products.

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