slides on hyperconjugation by konain

1. 6/22/2020 1

2. Hyper-conjugation
 Resonance involves
delocalization of π electrons,
leaving the σ bond untouched.
 However in some cases, a σ bond
and an adjacent π bond may get
involved in resonance.
 Such a delocalization is called as
Hyperconjugation.
 It is a stabilizing effect of the
molecule.
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3. Hyper-conjugation
 Hyperconjugation occur in
following types of molecules such
as;
Carbocations
 free radical
 alkenes and
 alkynes.
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4. Hyperconjugation in
carbocations:
 Hyperconjugation occur in carbocation for
example in butyl carbocation.
 Butyl carbocation has 9 alpha hydrogen and
hence 9 Hyperconjugation structures can be
written.
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5. Hyperconjugation in free radicals:
 Hyper conjugation in free radicals for
example in ethyl free radical.
 A radical is explained where there is an
overlap between the p orbital occupied by
the odd electron and σ orbital of the alkyl
group (Hyperconjugation).
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6. Hyperconjugation in alkenes:
 Hyperconjugation in alkenes for example in
propene.
 Hyper conjugation arise due to partial overlap
of sp3 sigma bond orbital and the empty p-
orbital of an adjacent carbon atom. Here one
of the carbon-hydrogen bonds of methyl
group can lie in the plane of pi-bond orbital,
hence partial overlap with pi-bond orbital.
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7. Hyperconjugation in alkynes:
 Hyperconjugation in alkynes for example in
propyne.
 Higher substituted alkynes are more stable
than their lower substituted (terminal)
isomers.
 The reason for this behavior is the
Hyperconjugation of the π orbitals with the
sp3 hybrid orbitals of the alkyl groups.
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