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Both [2+2] and [6+2] are _____ forbidden but ____ allowed
- Thermally (ground state)
- Photochemically (the electron excited state)
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Photochemical induction
When energy is added through photons. Excites an electron from the HOMO to the LUMO
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For MO diagrams: thermal is at the ____ state and photochemical is at the ____ state
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Syn dihydroxylation: What does it add to the double bond and what reagents are used
Adds a 1,2 diol
Uses either OsO4 with H2O2
Or
KMnO4 in cold, dilute conditions
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What does a triple bond form when it reacts with KMnO4
A 1,2 carbonyl instead of a 1,2 diol
But it goes through a transition state where there are 4 alcohols
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What are the conditions needed for oxidative cleavage?
Harsh conditions:
concentrated KMnO4 with heat and acid for workup in last step
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In oxidative cleavage, a primary carbon becomes an ____ after going through an _____ intermediate, and a secondary carbon becomes a _____
Acid, after aldehyde intermediate
Ketone
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During oxidative cleavage, a terminal alkene or alkyne will create ____ product(s). This is because _____
One product
Carbon dioxide forms and is removed from the solution as a gas
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During oxidative cleavage, an internal alkene or alkyne will create ____ product(s)
Two
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What happens when oxidative cleavage involves IO4-?
The oxidation of primary carbons stops at the aldehyde instead of proceeding to the acid
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Cleavage involving ozonolysis: Ozone is a mild ____ agent and uses _____ or zinc. It stops primary carbons at the _____
- Mild reducing agent that uses DMS (dimethyl sulfide)
- Stops primary carbons at the aldehyde
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What are pericyclic reactions and what are the three types?
Reactions that flow through a cyclic transition state
- Cycloaddition
- Electrocyclic reaction
- Sigmatropic rearrangement
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How do you distinguish between cycloaddition, electrocylic reactions, and sigmatropic rearrangement?
Cycloaddition- two reactants become one product ([4+2])
Electrocyclic reaction- Something that is already cyclic turns into something else that is cyclic, but only involves one molecule
Sigmatropic rearrangement- the bonds within something that is cyclic rearrange themselves. Also involves only one molecule
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What is the diels alder reaction?
A [4+2] cycloaddition reaction that creates new carbon-carbon bonds. Involves a diene and dieneophile
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In a cycloaddition reaction, the diene acts as the ____ while the dienophile acts as the ____
Nucleophile
Electrophile
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Because both ends of the diene must be close to the dieneophile to react, the diene must be in the s-____ position and not the s-____
Cis
Trans
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Why is the stereochemistry of the diels-alder reaction conserved?
Because it proceeds via a concerted mechanism
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What are two things that limit a diene in the diels-alder reaction?
If the diene is in s-trans, and if it is sterically hindered
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Assuming the diene is on the top and the dienophile is on the bottom, is the endo or eco product favored and why?
The endo product is favored, because there is favorable pi bond overlap during this conformation
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In the endo product, the EWG is facing _____. In the exo product, the EWG is facing ____.
Down
Up
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On the diene, substituents on the outside go ___ while those on the inside go ____
Down
Up
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Is the dials-alder reaction reversible?
Yes, the retrosynthetic diels alder proceeds with the same mechanism, just backwards
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What happens to primary carbons when H2O2 is present as the second step during ozonolysis?
The aldehyde reacts completely to become an acid
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