BC.06 Double bonds, configurations and conformations

Detail how and when sp² hybridisation occurs.

In for example ethene molecules, sp² hybridisation occurs to create a 120 degree trigonal planar shape. 1 2s orbital and 2 2p orbitals combine to form 2 sp² hybrid orbitals.

Draw an energy level diagram for molecular orbitals in ethene.

What is the bond strength and length of a sigma bond and a pi bond?

Draw the cis and trans configurations of an ethene molecule

What are conformations?

Rotations around single bonds

Illustrate eclipsed and staggered conformations of an ethene molecule.

What is the energy cost for changing conformations (rotating bonds) between staggered and eclipsed?

10 kJ/mole

What are the different staggered conformations?

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What is the energy cost to rotate the bond to create the different staggered conformations?

Draw the 4 conformations (2 bonding orbitals, 2 anti-bonding orbitals) of a 1,3-butadiene molecule, showing the nodes.

Benzene, an sp² hybridised aromatic molecule, has at least 6 conformations and all 6 electrons of the delocalised pi system. Draw 6 conformations of benzene.

Pyridine and pyrimidine are all heterocyclic aromatic molecules that are sp² hybridised. Draw the electron orbitals of pyrrole, decide whether is it sp² hybridised and detail how stable this molecule is in comparison to pyrimidine/pyridine.