Which Cyclohexane-1,2- or 1,3-Diol Isomer is Most Stable?

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Discussion Overview

The discussion revolves around the stability of different isomers of cyclohexane diols, specifically comparing cis and trans configurations of 1,2- and 1,3-diol isomers. Participants explore the implications of hydrogen bonding and steric interactions in determining stability, with a focus on theoretical reasoning and model visualization.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants propose that cis isomers with adjacent OH groups may lead to hydrogen bonding, suggesting that cis-cyclohexane-1,2-diol could be the most stable.
  • Others argue that the trans configuration may reduce repulsion due to the distance between OH groups, questioning the stability of cis isomers.
  • A participant notes that when one OH is in the equatorial position, the distances from vicinal cis and trans positions are equidistant, complicating the stability assessment.
  • There is a suggestion that both cis-cyclohexane-1,2-diol and trans-cyclohexane-1,2-diol could be roughly equal in stability, challenging the idea that one is definitively more stable than the other.
  • Another participant mentions that the answer key indicates cis-cyclohexane-1,3-diol as the most stable form, citing optimal hydrogen bonding distances in this configuration.
  • Concerns are raised about the lack of molecular models during exams, which may affect participants' ability to visualize and understand the stability of the isomers.

Areas of Agreement / Disagreement

Participants express differing views on which isomer is most stable, with no consensus reached. Some believe that both cis and trans configurations of 1,2-diol are comparable in stability, while others highlight the superiority of the 1,3-diol configuration based on hydrogen bonding considerations.

Contextual Notes

The discussion reflects uncertainty regarding the influence of steric effects and hydrogen bonding on stability, with participants acknowledging the complexity of the interactions involved. There are also references to the limitations of not having physical models to aid in understanding the spatial relationships of the isomers.

Krushnaraj Pandya
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Homework Statement


Among the following, which should be the most stable compound?
1)Cis-cyclohexane-1,2-diol
2)Trans-cyclohexane-1,2-diol
3)Cis-cyclohexane-1,3-diol
4)Trans-cyclohexane-1,3-diol

Homework Equations


--

The Attempt at a Solution


My thought process is-cis isomers with adjacent OH groups lead to Hydrogen bonding so 1) should be the most stable, I'm not sure if repulsion will be the dominating factor and change the answer- what is the correct way to think about this?
 
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Krushnaraj Pandya said:

Homework Statement


Among the following, which should be the most stable compound?
1)Cis-cyclohexane-1,2-diol
2)Trans-cyclohexane-1,2-diol
3)Cis-cyclohexane-1,3-diol
4)Trans-cyclohexane-1,3-diol

Homework Equations


--

The Attempt at a Solution


My thought process is-cis isomers with adjacent OH groups lead to Hydrogen bonding so 1) should be the most stable, I'm not sure if repulsion will be the dominating factor and change the answer- what is the correct way to think about this?
Hydrogen bonding is the right idea, but why favor 1) over 2)? If the OH groups are trans equatorial, their geometrical relationship is the same as for cis gauche. Also, repulsion will definitely be a factor for the vicinal diols.
 
TeethWhitener said:
Hydrogen bonding is the right idea, but why favor 1) over 2)? If the OH groups are trans equatorial, their geometrical relationship is the same as for cis gauche. Also, repulsion will definitely be a factor for the vicinal diols.
doesn't trans mean they're farther away therefore reducing the effectiveness of hydrogen bonding? At least relative to the cis configuration
 
Krushnaraj Pandya said:
doesn't trans mean they're farther away therefore reducing the effectiveness of hydrogen bonding? At least relative to the cis configuration
This is where a molecular model comes in handy. When one OH is in the equatorial position of the chair conformation, it is equidistant from the vicinal cis and vicinal trans positions.
 
Alright, I looked at the model and saw the truth in that. But now both 1) and 2) can be correct- how do we gather that 2 is the correct option?
 
Also the fact that I won't have models in the exam puts me at unease...but I'll just have to remember I guess
 
Alright, confusingly -I found that the answer key says the most stable form is cis-cyclohexane-1,3-diol
 
Krushnaraj Pandya said:
Alright, I looked at the model and saw the truth in that. But now both 1) and 2) can be correct- how do we gather that 2 is the correct option?
2 is not the correct option. 1 and 2 will be roughly equal in stability. My point was to steer you away from 1 and 2.
Krushnaraj Pandya said:
Alright, confusingly -I found that the answer key says the most stable form is cis-cyclohexane-1,3-diol
Yes. Hence in post 2 where I said that hydrogen bonding is key. The distances involved in hydrogen bonding are optimal in the 1,3 diol. The distances are too small (and roughly equal) for the vicinal diols.
 
sorry for the late reply, we just have so much coursework that it is proving hard to review previous questions. Please forgive me if I forget to thank you for taking the time to help me, I'll try to reply with a better understanding as soon as I can, thank you :D
 

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