Chap 15,16 conjugate

Chap 15,16 conjugate - Chap 15 Conjugated systems...

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1 Chap 15 Conjugated systems Conjugated pie systems- more stable more stable Able to delocalize electrons- bond distance of 2 to 3 is shorter. Explore butadiene molecular orbital structure. π 1 π 2 π 3 π 4 HOMO LUMO 1. Diels Alder reactions - 4 + 2 cycloadditions
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2 HOMO LUMO + heat diene + dienephile (e’ rich) + (e’ poor) Possibilities- (EW = -C=O, -CN) 1. EW on dienophile + EW EW concerted Heat EX. + CN CN Heat 2. Mixed, ED on diene EW on dienophile ED or DE and EW Partial resonance forms that determine reactivity. ED group ED ED and DE DE EW group
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3 EW EW Line up for reactivity. Two possibilities. A) ED EW Heat ED EW Example: OCH 3 + CHO Heat OCH 3 CHO B) + EW Heat DE DE EW Example: + Heat H 3 CO H 3 CO O O 3. Stereochemistry of Diels-Alder rxn. Concerted mechanism so stereochem is retained. a. dienophile stereochem
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4 O OCH 3 OCH 3 O + Heat OCH 3 O OCH 3 O H H cis- O OCH 3 H 3 CO O OCH 3 O OCH 3 O H trans H b) deiene stereochem + Heat OCH 3 O OCH 3 O cis- trans COOCH
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Chap 15,16 conjugate - Chap 15 Conjugated systems...

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