Cycloalkane Numbering Confusion: Which is Right?

[rajeshmarndi]

Homework Statement

In one internet site it is 1-propyl-2-methylcyclopentane and in other it is 1-ethyl-2-propylcyclohexane

Homework Equations

The Attempt at a Solution

I know when two different substituents could receive the same number, number them by alphabetical order. So I can understand 1-ethyl-2-propylcyclohexane but it contradict with 1-propyl-2-methylcyclopentane. Are they both right?

 

[Borek]

Wouldn't hurt to see the molecule in question (especially taking into account cyclopentane and cyclohexane are two completely different backbones).

 

[rajeshmarndi]

Wouldn't hurt to see the molecule in question (especially taking into account cyclopentane and cyclohexane are two completely different backbones).

 

[Borek]

These are two different molecules.

 

[rajeshmarndi]

These are two different molecules.

They both are cycloalkanes, I wanted to know how are they numbered for nomenclature.

 

[insightful]

I learned alphabetical order or by complexity. Your first example uses neither. Maybe the rules have been liberalized.

 

[rajeshmarndi]

If there are two substituent consecutively in a cycloalkane, I think it shouldn't matter which ever substituent is numbered 1, because it wouldn't change the molecular structure.

That is,
1-propyl-2-methylcyclopentane or 1-methyl-2-propylcyclopentane,
1-ethyl-2-propylcyclohexane or 1-propyl-2-ethylcyclohexane

Also if there were more than two substituent, they can be numbered , from left or from right.

 

[insightful]

As long as it's unambiguous, I guess it's OK...fewer rules to have to remember.