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

In summary, the conversation discusses the comparison of bond energy in ethane, ethene, and ethyne, and the apparent contradiction between their acidity and bond energy. The participants clarify that the bond energy being referred to is the bond dissociation energy, which is not directly related to acidity. They also explain that the bond energy in ethane is defined by the energy required for homolytic bond cleavage.
  • #1
Krushnaraj Pandya
Gold Member
697
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
  • #2
Which bond energy? CC or CH?
 
  • #3
Borek said:
Which bond energy? CC or CH?
CH, sorry for the ambiguity
 
  • #4
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.
 
  • #5
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?
 

1. What is the bond energy paradox in ethane, ethene, and ethyne?

The bond energy paradox refers to the observation that the bond dissociation energies of the carbon-hydrogen bonds in ethane, ethene, and ethyne do not follow the expected trend based on bond order. For example, the bond dissociation energy of a single bond in ethane is higher than that of a double bond in ethene, which goes against the usual trend of double bonds being stronger than single bonds.

2. What causes the bond energy paradox in these molecules?

The bond energy paradox is primarily caused by differences in bond length and bond strength. Carbon-hydrogen bonds in ethane, ethene, and ethyne have different bond lengths and strengths due to the nature of the bonds and the hybridization of the carbon atoms. This results in unexpected bond dissociation energies for these molecules.

3. How does acidity relate to the bond energy paradox in these molecules?

Acidity is a measure of a substance's ability to donate a proton. In the case of ethane, ethene, and ethyne, the bond energy paradox affects the stability of the carbon-hydrogen bonds, making them more susceptible to breaking and releasing a proton. This is why these molecules are considered to be relatively acidic.

4. Can the bond energy paradox be explained by quantum mechanics?

Yes, quantum mechanics can provide a more detailed understanding of the bond energy paradox. This phenomenon can be explained by the concept of molecular orbital theory, which takes into account the wave nature of electrons and their interactions within a molecule. The differences in bond length and strength in ethane, ethene, and ethyne can be attributed to the different hybridization of the carbon atoms, which affects the distribution of electrons in the molecule.

5. How does the bond energy paradox impact the reactivity of these molecules?

The bond energy paradox has a significant impact on the reactivity of ethane, ethene, and ethyne. Due to the relatively weak carbon-hydrogen bonds and the high acidity of these molecules, they are highly reactive and can easily undergo various chemical reactions. This is why they are commonly used in organic chemistry reactions and are considered important intermediates in many industrial processes.

Similar threads

Energy level Diagram relating to SP3 hybridization
    • Biology and Chemistry Homework Help
Replies
2
Views
5K
Is my fictional Solar System stable and realistic?
    • Sci-Fi Writing and World Building
Replies
21
Views
1K
Quantum challenge: mathematical paradoxes
    • Quantum Physics
Replies
19
Views
3K
Geomagnetic Reversal 41k BP 240 years Paradox? Mechanism?
    • Earth Sciences
Replies
2
Views
5K
I Debunking the Myth of the Devil's Racetrack in Death Valley
    • Classical Physics
Replies
9
Views
2K
BRS: Those Damnable Paradoxes I. Overview
    • Special and General Relativity
Replies
19
Views
2K
The Relativity of Mass: Exploring the Concept of Relativistic Mass in Physics.
    • Other Physics Topics
2
Replies
50
Views
5K
The laws of Coulomb versus Ampere and the electromagnetic Machian paradox
    • Electromagnetism
Replies
15
Views
7K
[Novel] On usage of charged black holes for energy production and interstellar travel
    • Beyond the Standard Models
Replies
1
Views
2K
Anomalous Quasar Observations 200k Light Year Jet? And So On.
    • Astronomy and Astrophysics
Replies
11
Views
4K

Hot Threads

Recent Insights

Back
Top