Numbering

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Nicole Gamboa 2M
Posts: 21
Joined: Wed Sep 21, 2016 2:56 pm

Numbering

Postby Nicole Gamboa 2M » Tue Mar 14, 2017 8:51 pm

Hi All,
I was confused about how to number cycloalkenes and why it doesn't follow the general rule of thumb that you want all of the substituents have lower numbers. Specifically at the bottom of p.28 in the Intro to Organic Chemistry book it gives an example about the correct way to number a cycloalkene, but in the example it has the substituents numbered 1 and 5 rather than 2 and 3. I was just wondering why would that be the case and why don't you look at the combination of both substituents?
Thanks!

Christopher Reed 1H
Posts: 33
Joined: Wed Sep 21, 2016 2:57 pm
Been upvoted: 1 time

Re: Numbering

Postby Christopher Reed 1H » Tue Mar 14, 2017 9:15 pm

Hi!

The rule is that you want the absolute lowest number on a substituent, not the lowest sum. As the course reader states 1<2, so the name including 1 is correct. Just for an example, if I as picking between a name that had the numbers 2 and 3 or a name that had the numbers 1 and 14 (not really sure if this is possible, just an example), you would choose the latter because it includes 1: the absolute lowest number out of the two options.


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