## Numbering

Jasmine Alcantara 3G
Posts: 18
Joined: Wed Sep 21, 2016 2:58 pm

### Numbering

For numbering multiple constituents, do we always make the first constituent the lowest possible number even when sacrificing a smaller overall number total? Or are we going for the lowest sum total?

Mannat Sukhija 1E
Posts: 23
Joined: Fri Jul 22, 2016 3:00 am

### Re: Numbering

I believe you want to aim for the first number to be as small as possible opposed to a smaller sum of substituent numbers.

Janice Kim 3I
Posts: 33
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Numbering

Hey! When numbering multiple constituents, always aim for the lowest sum total. If there is equal numbering between constituents (for example 2,3 or 3,2) then apply the lowest number to the first alphabetical constituent, not including the prefixes.

DBaquero
Posts: 13
Joined: Wed Sep 21, 2016 2:59 pm
Been upvoted: 1 time

### Re: Numbering

I believe Professor Lavelle told us to aim for the lowest first number. If the first number would be the same either way then aim for the lowest second number as well (and so on).

andrea_Disc3D
Posts: 10
Joined: Wed Sep 21, 2016 2:55 pm

### Re: Numbering

I heard someone say that you should also number a molecule so that you have the most substituents. I was wondering if anyone knew whether this was true or not?

ribal_daniel_3H
Posts: 13
Joined: Wed Sep 21, 2016 2:58 pm

### Re: Numbering

The way I see it is that we should strive to have the longest carbon chain. Also you want the first number to be the lowest I think. So if you have a 2 or 4-methyl and a 2 or 4-ethyl on a pentane, you would write 2-ethyl-4methylpentane.

angelicapayne
Posts: 10
Joined: Wed Sep 21, 2016 2:58 pm
Been upvoted: 1 time

### Re: Numbering

My TA mentioned the sum rule works only in some cases so it is not always a reliable way to determine numbering

Posts: 110
Joined: Fri Sep 24, 2021 7:06 am

### Re: Numbering

I think that we have to do the lowest first number and then make sure that you have the most substituents.

Jennifer Kainth 3L
Posts: 103
Joined: Fri Sep 24, 2021 6:11 am

### Re: Numbering

Professor Lavelle had told us to aim for the lowest first number. If the first number is the same, the second lowest number is your next option.

Casey Fineberg
Posts: 34
Joined: Mon Jan 03, 2022 9:55 am

### Re: Numbering

When numbering multiple constituents in organic compounds, the general rule is to assign the lowest possible number to the first constituent and then proceed to assign the lowest numbers to the other constituents in alphabetical order.

405718358
Posts: 30
Joined: Mon Jan 09, 2023 9:07 am

### Re: Numbering

what I remember being told is that we should always try to assign lowest number possible to the first constituent.