Question 8.4: Identifying hybridization and Orbital Overlap in Single and ...
Identifying Hybridization and Orbital Overlap in Single and Double Bonds
Propylene, C_{3}H_{6}, a starting material used to manufacture polypropylene polymers, has its three carbon atoms connected in a row. Draw the overall shape of the molecule, and indicate what kinds of orbitals on each atom overlap to form the carbon–carbon and carbon–hydrogen bonds.
STRATEGY
Draw an electron-dot structure of the molecule and count the number of charge clouds around each carbon atom. Use the number of charge clouds and the VSEPR model to predict geometry and hybridization.
A molecule with the formula C_{3}H_{6} and its carbons connected in a row does not have enough hydrogen atoms to give each carbon four single bonds. Thus, propylene must contain at least one carbon–carbon double bond. In the structure of polypropylene, the carbon atom on the left has four charge clouds (four single bonds) and tetrahedral geometry with sp^{3} hybrid orbitals. The other carbon atoms have three charge clouds (two single bonds and one double bond) and trigonal planar geometry with sp^{2} hybrid orbitals. The carbon on the left has bond angles of 109.5° and the other carbon atoms have bond angles of 120°.
The carbon–carbon single bond is formed by an overlap of an sp^{3} orbital and an sp^{2} orbital. The carbon–carbon double bond consists of σ bond formed from head on overlap of two sp^{2} hybrid orbitals and a π bond formed from sideways overlap of two p orbitals. Each carbon–hydrogen bond is formed from overlap of a hydrogen 1s orbital with the hybrid orbital on the carbon to which it is attached.