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So while calculating for the relative yield of monochlorination for 2,3-dimethylbutane, I was counting the primary hydrogens, I counted 6, but in fact it was 12. Why is it 12? How do you find equivalent hydrogens? Since the compound is symmetrical doesn't the hydrogens on both sides be equivalent to each other?

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The hydrogen atoms in a methyl group are equivalent to each other. There are 4 methyl groups and therefore there are 12 equivalent hydrogens. 2,3-dimethylbutane is symmetric as you stated, and so on one side you have 6 equivalent hydrogens, this implies that there are 6 more equivalent hydrogens on the opposite side.

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  • $\begingroup$ actually there are 2 pairs of 6 equivalent protons and 2 pairs of 6 enantiotopic protons. $\endgroup$ – ron Apr 19 '15 at 15:09
  • $\begingroup$ @ron Ah, I see. Then that means she was correct in that there are only 6 equivalent protons? $\endgroup$ – Jun-Goo Kwak Apr 19 '15 at 15:12
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    $\begingroup$ Yes, but note that both the equivalent and enantiotopic hydrogens will not be distinguishable by an achiral reagent (a chlorine free radical in this case) . So there are 12 primary hydrogens, it is just not the best terminology to say that they are all equivalent. $\endgroup$ – ron Apr 19 '15 at 16:40

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