stereochemistry of reaction
Why can the top happen, but the bottom cant? is it to do with trans-diaxial orbital stuff?
This doesn't really make any sense, who told you that the top reaction would happen but the bottom one wouldn't? The only thing different between the two enantiomers is the fact the hydrogen on the carbon alpha to the nitrile carbon is equatorial in the top enantiomer and axial in the bottom. However, this hydrogen does not move during the reaction so is of no significance.
What year are you? Those arrows on the right are retrosynthesis arrows, so this is stating that you cannot form the bottom regioisomer due to there being a problem with the transition state. This reaction is a 4s+2s cyclo-addition, otherwise known as a Diels Alder reaction. The furan is the diene, the acrylonitrile is the dieneophile. As the nitrile is an electron withdrawing substituent, we have an electron deficient dienophile. The oxygen of the furan ring is electron donating, so we have an electron rich diene. Therefore we have normal electron demand, meaning that for the orbital explanation of this reaction, we use the HOMO of the diene and the LUMO of the dieneophile.In the top reaction, we have the exo product. In the bottom product, we have the endo product. In the endo transition state of this Diels Alder reaction, there is a favourable secondary orbital interaction meaning that the endo transition state should be stabilised over the exo, even though there is a higher degree of steric crowding. Hopefully this drawing shows what I mean by the secondary orbital interaction. In the second step, after the bonds have been formed through the cycloaddition, the dieneophile flips round, meaning that the nitrile will be on the same face as the oxygen.. which is why I'm confused.
What year are you? Those arrows on the right are retrosynthesis arrows, so this is stating that you cannot form the bottom regioisomer due to there being a problem with the transition state. This reaction is a 4s+2s cyclo-addition, otherwise known as a Diels Alder reaction. The furan is the diene, the acrylonitrile is the dieneophile. As the nitrile is an electron withdrawing substituent, we have an electron deficient dienophile. The oxygen of the furan ring is electron donating, so we have an electron rich diene. Therefore we have normal electron demand, meaning that for the orbital explanation of this reaction, we use the HOMO of the diene and the LUMO of the dieneophile.In the top reaction, we have the exo product. In the bottom product, we have the endo product. In the endo transition state of this Diels Alder reaction, there is a favourable secondary orbital interaction meaning that the endo transition state should be stabilised over the exo, even though there is a higher degree of steric crowding. Hopefully this drawing shows what I mean by the secondary orbital interaction. In the second step, after the bonds have been formed through the cycloaddition, the dieneophile flips round, meaning that the nitrile will be on the same face as the oxygen.. which is why I'm confused.
Quick Reply
Related discussions
- Chemistry at Uni?
- chemistry a level
- (AQA AS Chemistry) Redox reactions - help!
- Allergic
- AS Chemistry question
- A level chem Mc question help
- chemistry help
- Factors affecting reaction time
- Biology rate of reaction question
- bio help a level
- equilibriums in reversible reactions
- Physics question- man in lift
- Chemical equations gcse alevel
- AS/A Level Chemistry Study Group 2023/2024
- Chemistry IA.
- Maths Question Help Urgent!
- Ocr a level chem
- Reaction Rates
- [Chemistry] Equilibrium Question
- Math moments
Latest
Last reply 52 minutes ago
Official University College London Applicant Thread for 2024Last reply 57 minutes ago
Can I do economics degree without a level maths?Last reply 1 hour ago
How to choose unis in UCAS application for CS undergraduate course?Last reply 1 hour ago
Rishi Sunak pledges to remove benefits for people not taking jobs after 12 monthsLast reply 2 hours ago
Got my crush's number 2 days ago and no reply yet. What could be the reasons?Posted 2 hours ago
GB News set to axe 40 jobs after channel posts heavy lossesLast reply 2 hours ago
Rwanda bill likely to be stalled at least till April after seven defeats in the LordsPosted 2 hours ago
Sunak rejects offer of youth mobility scheme between EU and UK
