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If I draw the structures of 2-bromo-4-chloropentane and 4-chloro-2-bromopentane, I get the same result, when I try to draw the structures. So why is it necessary to name prefixes alphabetically? Can we write IUPAC names not alphabetically?

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  • $\begingroup$ I think it's just a discipline.. nothing much. $\endgroup$ Oct 12, 2019 at 3:52

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With the preferred IUPAC name (PIN), there is exactly one way that you expect to find a compound written.

Assume you want to buy the compound from the chemical supplier of your choice but don’t have a CAS number at hand. What do you do? You search for the compound in the catalogue. In the old days, these were always paper books that you could use as a weapon but nowadays electronic catalogues exist too. Still, if you’re looking for 1-bromo-3-chloropentane but it is entered into the catalogue as 3-chloro-1-bromopentane, you’re going to have a very hard time searching for it.

There are also other reasons why having one defined standard way of naming compounds is strongly preferred over random but clear.

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  • $\begingroup$ As side note to the OP, for some weeks now, resources for learning chemistry includes a dedicated section «References about Nomenclature», too. $\endgroup$
    – Buttonwood
    Aug 16, 2021 at 17:15
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    $\begingroup$ Anyway, it is always better to have only one name for a given substance. Chemists may realize that 2-bromo-4-chloropentane and 4-chloro-2-bromopentane are one and the same substance. But the clerk at the customs, the manager and the caretaker may not be able to do this reasoning. $\endgroup$
    – Maurice
    Aug 18, 2021 at 9:39

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