Chapter 2 : Alkanes

sp² hybridisation

When a C atom is attached to 3 groups and so is involved in 3 σ bonds, it requires 3 orbitals in the hybrid set. This requires that it is sp² hybridised. The general "steps" are similar to that for seen previously sp³ hybridisation.
 

"Blend" (i.e. hybridise) the s and the 2 p orbitals... since we "mixed" 3 orbitals, we get a set of 3 sp2 orbitals the other p orbital remains unaffected each sp2 hybrid and the p orbital contains a single unpaired electron

You can view an animation of the hybridisation of the C orbitals if you wish.

In ethene, H2C=CH2 both C are sp2  hybridised. 4 C-H σ bonds are made by the interaction of C sp2 with H1s orbitals (see red arrows) 1 C-C σ bond is made by the interaction of C sp2 with another C sp2 orbital (see green arrow) 1 C-C π bond is made by the interaction of the C p with the other C p orbital (see black arrows)

Summary

• sp² occurs when a C has 3 attached groups
• sp² has 33% s and 67% p character
• the 3 sp² hybrids point towards the corners of a triangle at 120^o to each other
• each sp² hybrid is involved in a σ bond
• the remaining p orbital forms the π bond
• view a double bond as a σ + π bond

© Dr. Ian Hunt, Department of Chemistry