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Quick doubt on organic nomeclature

  1. Nov 22, 2008 #1

    When naming organic compounds, hydrocarbons for example, it's very common to have several radicals of the same group attached to the 'main' carbon line. So for example, pentane, with 5 carbons in a row. Suppose we add 2 methyl to it, one on carbon 2 and one or carbon 3. We'd then have to call it 2,3 dimethyl-pentane. Or suppose we add 2 methyl on carbon 2 and 2 more on carbon 3, it'd then be 2,2,3,3 tetramethyl-pentane.

    So my question is: if we have several radicals of the same group, do we always have to put the di, tri, tetra or whatever prefix before the group name? Like in the above examples, dimethyl, tetramethyl, because I assume that one can simply count how many methyl's we have on the molecule. So I don't see much of a purpose on adding a prefix. Also, instead of using di or tri, can we just use a number, like 2,3 2-dimethyl-pentane? Or it could cause ambiguity?

    Thanks in advance
  2. jcsd
  3. Nov 26, 2008 #2


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    You could do it your way and name the 2,2,3,3-tetramethylpentane just 2,2,3,3-methylpentane IF........ everyone did it that way and knew that you have to count the number of substitutions (2,2,3,3- would be 4, for example) and know that there are 4 of the radical that follows (-methylpentane). That's not the way it's done but it could be.

    Of course we would all have to learn yet another weird numbering system and remember that the preceeding numbers refer only to the radical(s) they are associated with.
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