Molecular Orbitals Practice Problems
Show how pi orbitals are involved in the formation of pi bonds in the given molecules.
Explain the cause of the rotational behaviors around the C−C bond in propane, which has a free rotation, and around the C=C bond in propene, which has an extremely high rotational barrier.
Provide a molecular orbital diagram for trans−hex−3−ene and label all σ and π bonds. Determine and explain whether there will be a free rotation around the C3−C4 bond or none.
A Lewis acid is a substance that can accept an electron pair. One example of a Lewis acid is SiH3+. Which orbital will the new electron occupy if SiH3+ accepts an electron pair?
Explain why the diagram below does not accurately represent the molecular orbital ψ2 of hexa−1,3,5−triene.
The molecular orbital drawing for the C—F bond of fluoromethane is given below. If there were two more electrons in this bond, where would these electrons go in the molecular orbital drawing?
a. Determine the number of molecular orbitals present in 1,3,5-heptatriene and the designation of its HOMO (such as Ψ1, Ψ2).
b. How many nodes are there in its highest energy molecular orbital?
a. Draw the end lobes of molecular orbitals of conjugated π-bonds in the following to show whether the HOMO is symmetric or antisymmetric.
i. A polyene with even numbers of π-bonds.
ii. A polyene with odd numbers of π-bonds.
b. Do these MOs follow the Woodward–Hoffmann rules given below?
- For an even number of π-bonds, an electrocyclic reaction occurs thermally with a conrotatory ring closure and photochemically with disrotatory ring closure.
- For an odd number of π-bonds electrocyclic reaction thermally with a disrotatory ring closure and photochemically with conrotatory ring closure.