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Topic: Homo/LUmo  (Read 1627 times)

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Offline Squeak1107

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Homo/LUmo
« on: May 09, 2016, 07:25:35 PM »
1) State whether the HOMO/LUMO energy gap in hexa-1,3-5-triene will be larger or smaller than in buta-1,3-diene. Explain how the consequence of this difference is seen in the ease of oxidation of these molecules.

As conjugation is greater in the trip-ene it follows that the HOMO/LUMO energy gap is lower as well. However I'm a little stuck on the oxidation part. As oxidation is loss of electrons would having a smaller homo/lumo gap make it easier to remove electrons as less energy would be needed? However if that is the case i don't quite understand why. Any help in clearing this up would be greatly appreciated!

Offline Corribus

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Re: Homo/LUmo
« Reply #1 on: May 10, 2016, 09:48:33 AM »
Oxidation is loss of electron from the HOMO. The "ease of oxidation" is essentially captured in the ionization potential - that is, how much energy it takes to remove an electron from an orbital. While you can remove an electron from any molecular orbital, it is easiest to remove those with the highest energy - i.e., those from the HOMOs. The quantity of energy required to remove the electron is basically identical to how much the orbital (in this case the HOMO) is stabilized with respect to the "free electron limit". So the question you need to ask yourself is, of the triene or diene, which one has the more stabilized (lower energy) HOMO? The more stabilized orbital is lower energy, and there it takes more energy to remove an electron in it = harder to oxidize.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline Squeak1107

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Re: Homo/LUmo
« Reply #2 on: May 10, 2016, 10:44:33 AM »
Thank you your explanation was very useful.Would I be correct in thinking that the di-ene has the lower energy HOMO so would be harder to oxidise?

Offline Corribus

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Re: Homo/LUmo
« Reply #3 on: May 10, 2016, 10:49:03 AM »
Yes, this is why more conjugated chromophores tend to be less stable.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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