l4 - O + O 2 new bonds formed at once! 4 thediene 2 the...

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Unformatted text preview: O + O 2 new bonds formed at once! 4 thediene 2 the dieneophile A A LUMO S LUMO A HOMO LUMO A HOMO HOMO S S S S LUMO HOMO or Arrows can go either way Arrows can go either way The diene must be in the s-cis configuration. s-trans s-cis 0 kJ +24 kJ +15 kJ O cyclohexa-1,3-diene furan cyclopenta-1,3-diene Some cyclic dienes work very well because they are locked into the s-cis conformation. s-trans s-cis H C CH 3 Atoms would H 3 C H 3 C CH 3 would collide! But with big subsituents sometimes you can not make s-cis . No Diels Alder possible. make s cis . No Diels Alder possible. s-trans s-cis + 200 o C + closed vessel The simplest Diels Alder reaction between butadiene and ethane is not very favorable. It has a very large energy of activation. How can we make the Diels Alder reaction more favorable? We can add substituents that enhance the flow of electrons of electrons. A S LUMO A LUMO Base LUMO A A LUMO HOMO S HOMO S HOMO S Acid How do you make something a better base? Raise this level How do you make something a better base? Add more electrons. Add an Electron Donating Group. (EDG) A Lower this level S LUMO A Base LUMO LUMO A A LUMO HOMO S HOMO S HOMO S Acid How do you make something a better acid? How do you make something a better acid? Remove electrons. Add an Electron Withdrawing Group. (EWG) The simplest Diels Alder reaction between butadiene and ethane is not very favorable. It has a very large energy of activation It has a very large energy of activation. How can we make the Diels Alder reaction more How can we make the Diels Alder reaction more favorable?...
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l4 - O + O 2 new bonds formed at once! 4 thediene 2 the...

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