Organic Chemistry
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Hyperconjugation Effect – Organic Chemistry

Learn bond fission mechanism, electrophile and nucleophile, inductive effect, mesomeric effect, and hyperconjugation in organic chemistry.

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Posted by Tushar Agarwal, 2/6/2021
Hyperconjugation Effect – Organic Chemistry

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There are some basic principles of organic chemistry that mainly include fission of covalent bonds, types of species based on relative electronegativity strength, and electron displacement effects. Earlier, we had discussed the Inductive effect, Mesomeric effect, and Electromeric effect. In this article, we will continue our discussion with the Hyperconjugation effect.

What is Hyperconjugation Effect?

It is a permanent effect that we observe in alkyl groups. Here, σ-electrons of the C-H bond delocalize in creating a double bond between adjacent C-C atoms. This happens by overlapping with the unshared p-orbital of the double bond. We know this as Hyperconjugation Effect or Baker Nathan Effect.

Orbital Overlapping in Hyperconjugation Effect
Hyperconjugation Effect

The resulting structures are called Hyperconjugative Structures. We can observe that there are no actual bonds present between C and H atoms in these structures. So, it is also known as No Bond Resonance. H atoms participating in this resonance are called α-Hydrogen atoms. Also, more α-H atoms imply more hyperconjugative structures and a prominent inductive effect as well.

Application of Hyperconjugation Effect

  1. Directive effect of alkyl groups: The influence of ortho and para-substituted CH3 and alkyl groups can be explained via the Hyperconjugation Effect.
Hyperconjugation in Methyl Benzene
Hyperconjugation in Methyl Benzene

As a result, the electron density increases at ortho and para positions. So, electrophilic substitution occurs at these sites.

2. Shortening of adjacent C-C bond: Due to Hyperconjugation effect, the C-C bond achieves some double-bond character. Consequently, the length of this bond becomes shorter compared to the C-C bond of propane.

Hyperconjugation in Propene
Hyperconjugation in Propene

3. Relative stability of alkenes, carbocation, and free radicals: Heat of hydrogenation has revealed that more alpha hydrogens increase the stability of alkenes, carbocation, and free radicals.

Reverse Hyperconjugation Effect

It is a similar effect operating in the reverse direction. Here, -CX3 groups are responsible for the effect, where X is halogen. When such a group is substituted on the aromatic ring, they deactivate ortho and para position towards electrophilic aromatic substitution. Hence, it is termed the reverse hyperconjugation effect.

Reverse Hyperconjugation in aromatic ring

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  1. Inductive Effect; Electrophile & Nucleophile – Organic Chemistry
  2. Mesomeric Effect and Electromeric Effect
  3. Hyperconjugation Effect – Organic Chemistry
  4. Geometrical Isomerism & Optical Isomerism

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