[jmarie16]

I'm having trouble understanding some of my teacher's chemistry slides. In it, it states:
"When there is both a functional group suffix and a substituent, the functional group suffix gets the lowest number"

Then the example is given as follows: CH₃CHCHCH₂CH₃ with a Cl atom on the second Carbon (if reading from left to right) and an OH group on the third.

The topic is on nomenclature of alcohols so I assume the functional group to be the OH group and therefore I would number from right to left, giving the OH group the lower number (3) and the Cl would be considered to be on C4. That would mean it is 4-chloro-3-pentanol, because I'm considering OH to be the functional group and 3 is the lower than 4. However, my teacher's notes say it is supposed to be 2-chloro-3-pentanol. Which confuses me because I thought Cl would be the substituent. Can anyone explain this to me?

PS- Sorry for the awful formatting, I'm new to this and not sure how to format structures in this box and trying to insert an image was equally as foreign to me. I'd really appreciate any explanation I can get

[discodermolide]

The substituents are arranged in alphabetical order in the name, hence chloro-hydroxy..
The numbering in such a compound is done so that the sum of the locants is lowest, in your example, 4-chloro-3-hydroxy gives 7 as the sum in the teacher's example, 2-chloro-3-hydroxy the sum is 5. Therefore the latter is chosen.

2-chloropentan-3-ol

[jmarie16]

thank you so much, that completely cleared things up for me!