How does the presence of a double bond influence alkene stability?

The presence of a double bond increases alkene stability due to the delocalisation of pi electrons.

In more detail, alkenes are hydrocarbons that contain a carbon-carbon double bond. This double bond is composed of a sigma bond and a pi bond. The sigma bond is formed by the overlap of sp2 hybrid orbitals, while the pi bond is formed by the sideways overlap of p orbitals. The pi electrons are not as tightly held as the sigma electrons, and are thus more delocalised. This delocalisation of electrons contributes to the stability of the alkene.

The stability of alkenes is also influenced by the substituents attached to the carbon atoms of the double bond. Alkenes with more substituents are generally more stable. This is because the substituents can donate electron density into the pi system, further stabilising the molecule. For example, tetrasubstituted alkenes (alkenes with four substituents on the double bond) are more stable than trisubstituted, disubstituted, or monosubstituted alkenes.

Moreover, the spatial arrangement of the substituents can also affect the stability of alkenes. Trans alkenes, where the substituents are on opposite sides of the double bond, are more stable than cis alkenes, where the substituents are on the same side. This is due to the fact that in cis alkenes, the substituents are closer together and can cause steric hindrance, which destabilises the molecule.

In summary, the presence of a double bond in alkenes increases their stability due to the delocalisation of pi electrons. The number and arrangement of substituents on the double bond can further influence this stability.