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Alkenes: Properties

Alkenes: Stability

The stability of alkenes increases with the number of alkyl substituents at the double bond. The data for butene isomers (C4H8) are shown in the table below.

Tab.1
Butene isomers, listed in order of increasing stability
Alkene
Fig.
1-butene
Fig.
cis-2-butene
Fig.
trans-2-butene
Fig.
isobutene
ΔH° [ kJmol-1 ] + 1.2 - 5.7 -10.0 -14.0

The stability gain of alkenes with increasing alkyl substitution at the double bond is due to hyperconjugation, which is caused by the interaction of one of the four sp3-hybrid orbitals of the CH3 group with the π* orbital of the double bond.

Fig.1
Hyperconjugation
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