3.1.9 Planarity of Organic Molecules

• Planar molecules have all their atoms in the same plane
  • Eg. linear, bent, trigonal planar and square planar

Molecules which have all their atoms in the same plane

• 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
  • Eg. ethene

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

• Eg. 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
  • For example, ethyne

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

• Eg. propyne

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