Take the 2-minute tour ×
Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers and students. It's 100% free, no registration required.

I was wondering about this specific scenario:
If you have a cyclohexane, for example, and the cyclohexane has two consecutive substituent groups, for example a methyl group and an ethyl group, how do you decide where the numbering starts?
Would it be 1-ethyl-2-methylcyclohexane or would it be 2-ethyl-1-methylcyclohexane? Whoever answers this, could you just give some sort of general rules on what to do in this situation (e.g. does it follow alphabetical order, etc.)?

share|improve this question

1 Answer 1

up vote 4 down vote accepted

If the numerical sequence of locants is equivalent, the numbering should be assigned to correspond with alphabetical order. Hence, in your example, correct would be 1-ethyl-2-methylcyclohexane. Quoting the IUPAC Blue Book, Rule A-2.4:

If two or more side chains are in equivalent positions, the one to be assigned the lower number is that cited first in the name.

share|improve this answer
    
Thank you so much. That clears up everything –  Nima Aug 20 at 21:13
    
@Nima, no problem, glad it helped. –  Greg E. Aug 20 at 21:14

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.