W2013CHM2311 Part 5 Notes

Combine with aos of central atom the pz orbital of

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Unformatted text preview: or a square species) S S ethylene ethylene cyclobutadiene Cyclic π- Systems: The Ring Cheat E nergy Cyclobutadiene: cyclo- C4H4 Cyclic π- Systems: The Ring Cheat Energy Cyclopentadienyl: cyclo- C5H5 The C5H5 anion – 6 π electrons 4n+2 Cyclic π- Systems: The Ring Cheat Energy Benzene: cyclo- C6H6 Analysis of π- Systems Hückel Molecular Orbital Theory makes the approxima0on that the π- system in a conjugated unsaturated molecule can be treated independently from the σ- framework of the molecule. ↳  Look at the π- orbitals and ignore the σ- orbitals – this makes the problem much simpler. ↳  Only consider side- to- side overlap of the p- orbitals to form π and π* MOs. From analysis of ethylene, allylic species and butadiene trends emerge. These trends can be applied to extended π- conju...
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