Determining Priority

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Ian Hurst 3L
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Joined: Fri Sep 25, 2015 3:00 am

Determining Priority

Postby Ian Hurst 3L » Sat Feb 27, 2016 6:28 pm

How do we determine which functional group has priority? Do we just have to memorize the list and just know, for example, that carboxylic groups have higher priority than alcohol groups? Is there another way to figure it out by looking at atomic mass or something? Also, for (E)-4-methlycyclopent-2-enol do we have to write (-en-1-ol) or is the 1 always assumed because we named the element after the priority functional group?

Ronald Yang 2F
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Joined: Fri Sep 25, 2015 3:00 am

Re: Determining Priority

Postby Ronald Yang 2F » Sat Feb 27, 2016 6:34 pm

I think the bigger the functional group and the greater the atomic number of the element in that functional group connecting with the rest of the molecule (usually shown as an "R" group) is a good indication of priority. It's also best to specify that one for the "-ol" because that will show that you understand that the priority starts with the OH. (Also, not sure how you got "4-methyl," since the highest it could be is 3).

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Re: Determining Priority

Postby Chem_Mod » Sat Feb 27, 2016 10:08 pm

The priority list is somewhat arbitrary and needs to be memorized. But there are many more on the full list than you really need to know for 14B. This is the "abridged" version:

carboxylic acid
alkoxy, halogen, and nitro are the 3 functional groups that are way at the bottom. They have the least priority in numbering, will never take a suffix, and are just alphabetized along with alkyl substituents in front of the name.

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