Carbon-Carbon Bond Energies: Primary vs. Tertiary Carbon

In summary, the bond energy for a bond containing a tertiary carbon is weaker than that of a bond containing a primary carbon due to steric hindrance and the stability of the resulting reactive species. The presence of more highly substituted carbons causes electron donation, lengthening the bond and decreasing its energy.
  • #1
blueblueblue
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Hi, first time poster.

Quick question:

Why is the bond energy for a bond that contains a more highly substituted (tertiary) carbon weaker than the bond energy of a bond that contains a less substituted (primary) carbon?

Let me clarify with an example. Say Bond A is a single bond between a methyl carbon and a carbon that has a double bond. Another bond (Bond B) also has a single bond but between a tertiary carbon and another carbon that has a double bond. So, both share an sp2-hybridized and an sp3-hybridized carbon. Now, I know that Bond B has a weaker bond energy because it contains the more highly substituted carbon, but I don't know why that is the case. I figured that the carbons pull some of the electron density away from Bond B, therefore, lengthening the bond and decreasing the bond energy. Is that correct?

Much thanks!

Edit: Hmmm. Now that I think about it, I don't know if this question should be posted on this board. Sorry about that.
 
Last edited:
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  • #2
Alkylation are actually electron donating groups. But the main reason usually boils down to simple steric hindrance. Bulkier groups cause more steric repulsion, weakening bonds. Furthermore, homolytically breaking the hypothetical bond in your examples creates either a methyl radical or an alkyl radical. Alkyl radicals are generally more stable, and for the reason I pointed out initially (electron donation into the half-filled p-orbital stabilizes the reactive species). So there are two thermodynamic effects working in tandem to destabilize tertiary carbon bonds.
 

1. What is a carbon-carbon bond?

A carbon-carbon bond is a type of chemical bond between two carbon atoms, in which they share electrons to form a stable covalent bond.

2. What is the difference between primary and tertiary carbon?

Primary carbon refers to a carbon atom that is directly bonded to one other carbon atom, while tertiary carbon refers to a carbon atom that is bonded to three other carbon atoms.

3. How does the number of carbon-carbon bonds affect the bond energy?

The number of carbon-carbon bonds in a molecule can affect the bond energy. Generally, as the number of bonds increases, the bond energy also increases. This is because more bonds means more shared electrons, resulting in a stronger bond.

4. Why do tertiary carbon-carbon bonds have higher bond energies?

Tertiary carbon-carbon bonds have higher bond energies because they have more bonds, which results in a stronger attraction between the atoms and a higher overall bond energy.

5. How can knowledge of carbon-carbon bond energies be useful in science?

Understanding carbon-carbon bond energies is important in many areas of science, such as organic chemistry and biochemistry. It can help predict and explain the reactivity, stability, and physical properties of molecules, and is also essential in designing and synthesizing new compounds for various applications.

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