Acidity and the bond energy paradox in ethane, ethene, ethyne

Click For Summary

Discussion Overview

The discussion revolves around the comparison of bond energies in ethane, ethene, and ethyne, particularly in relation to their acidity. Participants explore the apparent contradictions between bond energy and acidity, focusing on the hybridization of carbon atoms and the nature of bond cleavage.

Discussion Character

  • Homework-related
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant asserts that ethyne is more acidic than ethene and ethane due to the sp hybridization of carbon, which leads to a more polar CH bond and easier release of H+.
  • Another participant questions which bond energy is being referred to, specifically asking if it is the CC or CH bond energy.
  • A clarification is made that the CH bond energy is the focus, addressing previous ambiguity.
  • One participant argues that the bond energy does not equate to the energy required to abstract a proton, emphasizing that quoted bond energies typically refer to homolytic cleavage rather than ionic processes.
  • There is a challenge regarding the relationship between weaker CH bonds and acidity, questioning whether a weaker bond is generally considered more acidic.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between bond energy and acidity, with no consensus reached on how these concepts interrelate. The discussion remains unresolved regarding the implications of bond strength on acidity.

Contextual Notes

Participants note the complexity of defining bond energies and their relevance to acidity, highlighting potential ambiguities in the definitions and assumptions involved in the discussion.

Krushnaraj Pandya
Gold Member
Messages
697
Reaction score
73

Homework Statement


Compare bond energy of ethane/ene/yne

2. The attempt at a solution
Comparing their acidity, ethyne has sp hybridized C so more polar CH bond, therefore H+ can be released easily. Therefore acidity order is ethyne>ethene>ethane which means CH bond is weakest in ethyne and so has lowest bond energy but this is in fact reversed, I'm very confused regarding this apparent contradictions between two known facts. I'd appreciate some help
 
Physics news on Phys.org
Which bond energy? CC or CH?
 
Borek said:
Which bond energy? CC or CH?
CH, sorry for the ambiguity
 
The bond energy is not the energy required to abstract a proton.
I'm pretty sure anything you see quoted as the CH bond energy in ethane, for example, is defined by
C2H6 → 2C + 6H ΔH = E(CC) + 6 E(CH)
Even if it referred to a single bond cleavage, it would be a homolytic cleavage, not ionic, i.e.
C2H6 → C6H5⋅ + H⋅
not C2H6 → C6H5- + H+
Therefore acidity is not directly related to bond energy.
 
mjc123 said:
The bond energy is not the energy required to abstract a proton.
I'm pretty sure anything you see quoted as the CH bond energy in ethane, for example, is defined by
C2H6 → 2C + 6H ΔH = E(CC) + 6 E(CH)
Even if it referred to a single bond cleavage, it would be a homolytic cleavage, not ionic, i.e.
C2H6 → C6H5⋅ + H⋅
not C2H6 → C6H5- + H+
Therefore acidity is not directly related to bond energy.
isn't a weaker bond CH bond generally considered more acidic?
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
7K
  • · Replies 21 ·
Replies
21
Views
5K
  • · Replies 0 ·
Replies
0
Views
4K
  • · Replies 2 ·
Replies
2
Views
5K
  • · Replies 50 ·
2
Replies
50
Views
7K
  • · Replies 19 ·
Replies
19
Views
4K
  • · Replies 19 ·
Replies
19
Views
2K
  • · Replies 15 ·
Replies
15
Views
8K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 91 ·
4
Replies
91
Views
48K