Cycloalkane Numbering Confusion: Which is Right?

  • Thread starter Thread starter rajeshmarndi
  • Start date Start date
Click For Summary
SUMMARY

The discussion centers on the nomenclature of cycloalkanes, specifically the compounds 1-propyl-2-methylcyclopentane and 1-ethyl-2-propylcyclohexane. Participants highlight that both names can be correct depending on the numbering conventions applied, such as alphabetical order or complexity of substituents. The consensus is that as long as the numbering is unambiguous, variations in naming do not alter the molecular structure. The distinction between cyclopentane and cyclohexane backbones is also emphasized as significant in understanding these compounds.

PREREQUISITES
  • Understanding of IUPAC nomenclature for organic compounds
  • Familiarity with cycloalkane structures and their properties
  • Knowledge of substituent prioritization rules in organic chemistry
  • Basic grasp of molecular structure and isomerism
NEXT STEPS
  • Research IUPAC rules for naming cycloalkanes
  • Study the differences between cyclopentane and cyclohexane structures
  • Explore examples of complex substituent numbering in organic compounds
  • Learn about the implications of molecular structure on chemical properties
USEFUL FOR

Chemistry students, organic chemists, and anyone involved in the study or application of organic compound nomenclature and structure.

rajeshmarndi
Messages
319
Reaction score
0

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?
 
Physics news on Phys.org
Wouldn't hurt to see the molecule in question (especially taking into account cyclopentane and cyclohexane are two completely different backbones).
 
Borek said:
Wouldn't hurt to see the molecule in question (especially taking into account cyclopentane and cyclohexane are two completely different backbones).
cycloalkane.jpg
 
These are two different molecules.
 
Borek said:
These are two different molecules.

They both are cycloalkanes, I wanted to know how are they numbered for nomenclature.
 
I learned alphabetical order or by complexity. Your first example uses neither. Maybe the rules have been liberalized.
 
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.
 
As long as it's unambiguous, I guess it's OK...fewer rules to have to remember.
 

Similar threads

Replies
1
Views
2K
  • · Replies 11 ·
Replies
11
Views
6K
Replies
1
Views
3K
Replies
1
Views
1K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 29 ·
Replies
29
Views
5K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 2 ·
Replies
2
Views
5K
  • · Replies 4 ·
Replies
4
Views
16K
  • · Replies 4 ·
Replies
4
Views
71K