2. CONTENT
Introduction to Hyperconjugation
Conditions for Hyperconjugation
Types of Hyperconjugation
Effects of Hyperconjugation
Reverse Hyperconjugation
Reference
3. INTRODUCTION TO HYPERCONJUGATION
Introduced by Baker and Nathan.
Hyper means “EXCESSIVE”
It involves sigma orbitals of (CH Bond)
There is some ionic character between (CH Bond)
There is Σ-Π or Σ-P orbital overlape
It is a permanent effect
4. CONDITIONS FOR HYPERCONJUGATION
Compound should have sp2 hybride
carbon of alkene carbocation or free
radical.
α – carbon should have atleast 1 hydrogen i.e α-
hydrogen
It is also called as no bond resonance but as
carbon and hydrogen is present in the same
solution there is some interactions present
5.
6. TYPES OF HYPERCONJUGATION
Sacrificial Hyperconjugation Isovalent Hyperconjugation
There is charge separation between In this type of hyperconjugation there
resonating forms, although charge is a charge seperation in actual
dose not present on actual structure structure as well as resonating form.
7. HYPERCONJUGATION IN PROPENE
In structure II, III, IV, there is a shifting of ∑-electron
in C-H bond
Hyperconjugation in Toluene
8. EFFECTS OF HYPERCONJUGATION
Stability of alkenes-
More substitution falls for more stability so tetera
substituted alkene is more stable
Alkene <Monosubstituted <Bisubstituted < Trisubstituted
<Teterasubstituted
9. EFFECT ON BOND LENGTH
Due to the Hyperconjugation carbon-carbon bond of
alkene aquarires some double bond character and
carbon-carbon double bond acquire some single
bond character
So, the double bond length is increased and single
bond length is decreased
10. STABILITY OF FREE RADICALS
Due to hyperconjugation tertiary free radical is
more stable then primary free radical because
there are 9 α-hydrogen
11. REVERSE HYPERCONJUGATION
When there is electronegative atoms rather then
hydrogen atoms then this effect operate in reverse
direction. So, the conjugation in reverse system is
reverse Hyperconjugation
α – h(x)
α – Cl, F, Br, I
