Question

Is an alkane or alkene more stable? An alkene has a double bond which increases its stability and doesn’t allow for bond rotation. However, an alkene also has a low pKa.

Answer 1

Alkenes are less stable than alkanes.
In alkanes, there are only σ bonds (i. e. C-C single bonds and C-H bonds). The bond energy of an average C-C single bond is around 350 kJ/mol, and C-H bond around 300-450 kJ/mol, both of which need a relatively high energy to break.Since the electronegativities of C and H are close, there are no site in an alkane molecule with very high or very low electron density, results in very weak nucleophilicity or electrophilicity. However, under conditions such as light, heat and initiator, alkanes can undergo free radical reaction via homolysis of σ bonds.
Alkenes contains C-C double bond, which is a σ bond plus a π bond. The bond energy of an average C-C π bond is around 270 kJ/mol, which is lower than that of a C-C σ bond, and it is easier for alkenes to undergo addition or oxidation.