IUPAC Naming (1 Viewer)

[~ ReNcH ~]

I was doing a review exercise which asked for the name of the compound CH₃CHBrCHClCH₂CF₂CH₂Cl

I named it 5-bromo-1,4-dichloro-2,2-difluorohexane numbering the carbon chain from right to left in order to give the lowest numbers priority. However, the answer given was 2-bromo-3,6-dichloro-5,5-difluorohexane. I can understand that they numbered the chain from left to right but aren't you meant to number the chain so that you give the lowest numbers possible?

 

[Dreamerish*~]

You have to give the smallest number to the bromine, simply because it starts with "B".

Always name them alphabetically, giving the smallest number to the element at the front of the alphabet.

 

[~ ReNcH ~]

You have to give the smallest number to the bromine, simply because it starts with "B".

Always name them alphabetically, giving the smallest number to the element at the front of the alphabet.

Hmm...but what about this one:

CH₃CH₂CH₂CHBrCHClCH₃ which is named 3-bromo-2-chlorohexane according to the solutions, as opposed to 4-bromo-5-chlorohexane had I given the bromo the lowest number. (I got this one from a different book).

I was always under the impression that you numbered them so that you had the lowest numbers possible, and then listed them alphabetically.

 

[Dreamerish*~]

Hmm...but what about this one:

CH₃CH₂CH₂CHBrCHClCH₃ which is named 3-bromo-2-chlorohexane according to the solutions, as opposed to 4-bromo-5-chlorohexane had I given the bromo the lowest number. (I got this one from a different book).

I was always under the impression that you numbered them so that you had the lowest numbers possible, and then listed them alphabetically.

By lowest number, I don't mean in comparison to the other side groups.

I mean lowest number from the end of the chain, so if you start from the right side, you get 3-bromo, which is lower than starting from the left, where you would have 4-bromo.

 

[~ ReNcH ~]

By lowest number, I don't mean in comparison to the other side groups.

I mean lowest number from the end of the chain, so if you start from the right side, you get 3-bromo, which is lower than starting from the left, where you would have 4-bromo.

Ah ic.
So whether you number from the left or number from the right is based only on giving the first prefix the lowest number possible?

 

[Dreamerish*~]

Ah ic.
So whether you number from the left or number from the right is based only on giving the first prefix the lowest number possible?

Yes.

I'm also pretty sure that element-side-groups such as bromine and chlorine come before alkyl groups.

 

[AntiHyper]

You also have to disregard the "element-count" prefixes (eg. di/tri). Like, for some crazy molecule: 1-bromo-1,2,3,4-tetrachloro-2-fluoro-heptane

 

[Dreamerish*~]

You also have to disregard the "element-count" prefixes (eg. di/tri). Like, for some crazy molecule: 1-bromo-1,2,3,4-tetrachloro-2-fluoro-heptane

Disregard?

 

[Templar]

Disregard?

eg tetrachloro starts with c, not t. And halides get priority over alkyl groups.

 

[~ ReNcH ~]

Just another one:

CH₃CCl₂CHBrCH₃

This was named 3-bromo-2,2-dichlorobutane which doesn't give "bromo" the lowest number possible since it was numbered from left to right. Giving "bromo" the lowest number possible, it would be named 2-bromo-3,3-dichlorobutane instead i.e. numbering from right to left.

 

[Dreamerish*~]

Just another one:

CH₃CCl₂CHBrCH₃

This was named 3-bromo-2,2-dichlorobutane which doesn't give "bromo" the lowest number possible since it was numbered from left to right. Giving "bromo" the lowest number possible, it would be named 2-bromo-3,3-dichlorobutane instead i.e. numbering from right to left.

Hey, that's interesting.

Possibility one - the answer is wrong. Possibility two - the answers to the previous questions were wrong. Possibility three - there's another stupid rule.

Maybe because two chlorine side groups outrank one bromine side group? Bromine might have the letter "B", but it got owned because it was 2 on 1.