Planarity of Organic Molecules (Cambridge (CIE) AS Chemistry): Revision Note

Planar Molecules

• Planar molecules have all their atoms in the same plane

  • Eg. linear, bent, trigonal planar and square planar

 Examples of planar molecules

The diagram shows molecules which have all their atoms in the same plane with their name and the associated bond angle

• The presence of an sp² hybridised carbon can force the molecule to adopt a planar configuration (trigonal planar)

• The 3 σ bonds position themselves in a trigonal planar position so that the bonding pair of electrons are as far away from each other and therefore minimise the repulsion between them

The planarity of ethene

Ethene is a planar molecule with two trigonal planar centres around the carbon atoms

The planarity of propene

Propene has two trigonal planar centres around the carbon-carbon double bond and one tetrahedral centre

• The presence of an sp hybridised carbon can also force the molecule to adopt a planar configuration (linear)

• The 2 σ bonds position themselves in a linear position to minimise the repulsion between the bonding pairs of electrons

The planarity of ethyne

Ethyne is a planar molecule with one planar centre: the molecule is linear

The planarity of propyne 

Propyne has one planar centre around the carbon-carbon triple bond (linear) and one tetrahedral centre