# IUPAC name of trisubstituted benzene ring

What is the IUPAC name for the compound shown below? I named it as 6-Bromo-3-hydroxy benzonitrile according to the numbering scheme in 1b, since the priority order is $\ce{-CN} > \ce{-OH} > \ce{-Br}$.

However, the answer given in the book is 2-Bromo-5-hydroxy benzonitrile, which implies the numbering scheme in 1a. Please help me to identify whether my answer or the book's answer is correct.

• We compare the answer's [1,2,5] and your [1,3,6]. The first numbers (1 and 1) are the same; the second numbers (2 and 3) has the answer smaller than your attempt; therefore the answer is correct. – DHMO Oct 3 '16 at 15:39
• The priority order only determines which goes into the suffix. – DHMO Oct 3 '16 at 15:39
• Related (actually duplicate, but the other question is closed and includes proposed answers that are not related to the question): IUPAC name of bromo, cyano, hydroxy substituted benzene ring – Loong Oct 3 '16 at 16:00
• – Loong Oct 3 '16 at 16:04
• Numbering of carbons aside, there are two things I want to point out. Firstly, the first letter of the substituent should not be capitalised, so bromo is correct and not Bromo. Secondly, there is no space between the prefixes and the name of the parent compound, so there is no space between hydroxy and benzonitrile. – orthocresol Oct 3 '16 at 18:09

## 2 Answers

As -CN has the highest priority, root-word is benzonitrile. Lowest locant is 2 for -Br. So, the name given is: 2-bromo-5-hydroxybenzonitrile

As the functional group is -CN, with highest priority, no need to look for priority of -OH and -Br; just look for lowest locant.

I'm quite sure that you would typically name this as a substituted phenol. The name I would get for this is 4-bromo-3-cyanophenol. Whether or not this is 'strictly' IUPAC I'm not sure. When I searched this on Google, I found that SigmaAldrich was selling a constitutional isomer of this as 3-bromo-4-hydroxybenzonitrile, which would imply the previous answer is also acceptable. Frankly, it doesn't strike me as a critically important issue for most applications, since both names are completely unambiguous.