What is the Difference Between Isovalent and Sacrificial Hyperconjugation?

The key difference between isovalent and sacrificial hyperconjugation lies in the charge distribution and the types of structures involved. Hyperconjugation refers to the interaction of σ-bonds with a pi network. Here are the main differences between the two types of hyperconjugation:

• Isovalent Hyperconjugation:
• Occurs in free radicals and carbocations.
• The canonical form displays no charge separation.
• The main form has a charge separation.
• The contributing structure has the same number of two-electron bonds as the usual Lewis formula.
• Sacrificial Hyperconjugation:
• The canonical form involves no bond resonance.
• The main form has no charge distribution.
• This type of hyperconjugation is less common than isovalent hyperconjugation.

In summary, isovalent hyperconjugation involves free radicals and carbocations with no charge separation in the canonical form, while sacrificial hyperconjugation involves a lack of bond resonance in the canonical form and no charge distribution in the main form.

Comparative Table: Isovalent vs Sacrificial Hyperconjugation

The difference between isovalent and sacrificial hyperconjugation can be summarized in the following table:

In isovalent hyperconjugation, the interaction of σ-bonds with a pi network takes place in free radicals and carbocations, with the main form having no charge separation. On the other hand, sacrificial hyperconjugation occurs when the canonical form of a system involves no bond resonance, and one of the hydrogen atoms is missing from the structure, making the bond order of the alpha carbon atom approximately 1.