# Tag Info

Accepted

### How is exact racemization possible?

Racemization isn't "exact," but rather very very close to equality. It is just simple probability. Think of flipping a coin, p=probability for heads, and q=probability of tails. Now for a fair flip ...
• 21.4k

### Why do we get slightly more inversion product than retention product in SN1 reaction?

It is well known that SN1 reactions often give incomplete racemisation: Although many first-order substitutions do give complete racemization, many others do not. Typically there is 5–20% inversion, ...
• 16.7k
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### Why is the exo product formed in the Diels–Alder reaction between furan and maleic anhydride?

Great question! It turns out that the rate of formation of the "expected" endo product is actually ~500 times faster than the rate of formation of the exo product. However, the Diels–Alder is a ...
• 81.6k

### Why do we get slightly more inversion product than retention product in SN1 reaction?

As we know, $\ce{S_N1}$ reaction is stereochemically non specific. This means, that it does not force the formation of one stereoisomer, as $\ce{S_N2}$ does. In $\ce{S_N1}$ reaction, presence of ...
• 5,239
Accepted

### Stereoselectivity of dihydroxylation with osmium tetroxide

Dihydroxylation responds to steric effects and proceeds at less hindered positions. What will be the major product in the following reaction if the reagent used is osmium tetroxide followed by sodium ...
• 16.7k

### Why does the chlorination of indene occur with syn selectivity in heptane?

Key The reaction is run in heptane, a non-polar solvent. A non-polar solvent will not stabilize or support ions as well as a polar solvent. Background When the $\ce{Cl2}$ begins to interact with ...
• 81.6k
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### Models for diastereoselectivity in nitronate additions

Dave Evans taught me that you should generally analyze these types of problems by drawing out allyl conformations. I've drawn the nitronate to minimize 1,3-allylic strain. Now, the top face of the ...
• 16.7k
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### Why do Grignard reagents add to propargyl alcohols?

The addition of Grignards to propargyl alcohols occurs via the alkoxide salt, after deprotonation:[1] Here: the reactivity may be explained by the stabilising influence of complexation; the ...
• 65.5k
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### Why do stabilised ylids lead to trans alkenes in the Wittig reaction?

TL;DR: With stabilised ylids, the trans oxaphosphetane is formed, under kinetic control. This is due to minimisation of dipole-dipole repulsions in the transition state for oxaphosphetane formation: ...
• 65.5k
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• 63.6k

### Stereoselectivity of ring closure in intramolecular iodolactonisation

Without further details, I would say that both products are possible. The reaction that you have given here is an Iodolactonization reaction. You have correctly identified that the tert-butyl group ...
• 5,941

### Why do Zr, Sn, and Ti enolates form syn aldols selectively?

For most aldol reactions, the relative 1,2-diastereoselectivity is a consequence of the enolate geometry.* Both tin and titanium enolates are easily formed, and have been shown to exist predominantly ...
• 16.7k

### How can a ketone be enantioselectively reduced, in the presence of an ester?

I have had great results for enantioselective ketone reduction using the Noyori Ru-TsDPEN system. This has advantages through being catalytic with low stoichiometry and doesn't require high pressure, ...
• 2,131

### Stereo selective reaction products

Enyzmatic reduction (as would occur in yeast) could easily be a stereoselective process - probably via selective delivery of a hydride from NADH. As the other respondent notes, there is simply no way ...
• 126