Ordering of substituents?

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Ordering of substituents?

Postby Chem_Mod » Sat Oct 22, 2011 1:18 pm

Today in a review session, one of the TAs was going over naming of organic molecules, one molecule had a tert-butyl substituent as well as a fluorine substituent. He said that in numbering the molecule, the fluorine gets in the lower number because it has a greater molecular weight than the C of the tert-butyl. I thought the tert-butyl would get the lower number because it comes first alphabetically. Which is correct? Also, he said that ethers were a special case of functional group, and that double and triple bonds get priority over ethers in numbering. I thought that since an ether was a functional group, like any other functional group, it gets priority in numbering over double and triple bonds. Which is correct?

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Re: Ordering of substituents?

Postby Chem_Mod » Sat Oct 22, 2011 1:19 pm

Here is the order of functional groups. It is correct. From highest priority to lowest.


Cations> acids > amides, halides, esters, anhydrides > cyanides, nitriles > aldehydes > aldehyde derivatives > ketones > ketone derivatives > alchohols, phenols > hydroperoxides > ethers > peroxides

For seniority of chains-- chosen in accordance with the following criteria:

1. greatest # of principle groups on principle chain 2. greatest # of multiple bonds 3. greatest length 4. greatest # of double bonds 5. lowest locants for suffixes 6. lowest locants for multple bonds 7. lowest locants for double bonds 8. greatest # of prefix substituents 9. lowest locant for all substituents 10. the earliest letter of the alphabet for the first substiuent 11. lowest locant for the first prefix substituents in ABC order

WATCH OUT FOR THE DEFINTION OF SUBSTITUENT AND FUNCTIONAL GROUP.

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Re: Ordering of substituents?

Postby Chem_Mod » Sun Apr 28, 2013 5:59 pm

Are halogens always given higher priority when compared to carbon chains if they were both located on the same carbon in a geometric isomer? Thank you!

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Re: Ordering of substituents?

Postby Chem_Mod » Sun Apr 28, 2013 5:59 pm

No. See the post above for a prioritization list.


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