stereo chemistry. where is there space? the nucleophile was required to attack from the back. This is because if you imagine the epoxide ring as drawn, sticking up, the steric bulk it constitutes makes it impossible for the nucleophile to get through from that same side So, a backside attack from the nucleophile by default has to push the already present methyl group up.
steric bulk is an important factor to consider in SN1/SN2/E1/E2 reactions. it's why the 2 prime carbon was attacked to begin with, rather than the 3 prime (or more substituted) carbon.
Great, but your statement contradicts the video - it is the more substituted carbon that is attacked by the nucleophile in the case of acid catalysed ring opening of epoxides. The acid catalyzed reaction is Sn1-like in character because a partial positive charge develops on one of the ring carbons during the transition state. Since a more alkyl substituted carbon is better able to accomodate this charge (leads to a transition state of lower energy) attack at the more substituted carbon becomes the preferred pathway over attack at the less substituted - this stabilising of the transition state overrides steric considerations and the reaction becomes thermodynamically controlled rather than kinetically controlled (as in attack of a strong nucleophile on an unprotonated epoxide).
Students (including me at one time) would think that steric hindrance governs the overall scheme of where the SN2 attack goes. But in this case of Epoxide ring opening, steric hindrance favoritism is overruled by the "electronic effect" factor as Star Gazer points out, thereby regiochemistry will take precedence on tertiary (likely achiral) carbon centers. Kudos Gazer.
Yeah, Khan academy is never right! Don't you hate it when you've been studying OChem for like 35 minutes and start realizing doctors are getting it all wrong! note 1: Acid protonates epoxide to make --OH+--, then concerted mechanism happens...8 months later, you probably understand that by now, I hope. note 2: The Khan academy goes to great lengths not to use jargon, or material you may not have reached yet. They explain things with simple building blocks, not showing off their knowledge like most arrogant instructors.
Ring opening reactions? More like “Really good teaching actions.” Thanks again Khan Academy, for everything!
I'm just wowed by how much I gained from this video! Awesome explanation! Thanks. 😊
Good
Sir i have one doubt
During reaction 100% inversion..?
Or racemisation also there...??
Very good explanation. Just one question: Why did the methyl group get pushed up?
stereo chemistry. where is there space?
the nucleophile was required to attack from the back. This is because if you imagine the epoxide ring as drawn, sticking up, the steric bulk it constitutes makes it impossible for the nucleophile to get through from that same side
So, a backside attack from the nucleophile by default has to push the already present methyl group up.
steric bulk is an important factor to consider in SN1/SN2/E1/E2 reactions. it's why the 2 prime carbon was attacked to begin with, rather than the 3 prime (or more substituted) carbon.
Great, but your statement contradicts the video - it is the more substituted carbon that is attacked by the nucleophile in the case of acid catalysed ring opening of epoxides. The acid catalyzed reaction is Sn1-like in character because a partial positive charge develops on one of the ring carbons during the transition state. Since a more alkyl substituted carbon is better able to accomodate this charge (leads to a transition state of lower energy) attack at the more substituted carbon becomes the preferred pathway over attack at the less substituted - this stabilising of the transition state overrides steric considerations and the reaction becomes thermodynamically controlled rather than kinetically controlled (as in attack of a strong nucleophile on an unprotonated epoxide).
Students (including me at one time) would think that steric hindrance governs the overall scheme of where the SN2 attack goes. But in this case of Epoxide ring opening, steric hindrance favoritism is overruled by the "electronic effect" factor as Star Gazer points out, thereby regiochemistry will take precedence on tertiary (likely achiral) carbon centers. Kudos Gazer.
grasias
Well explained👏🏿👏🏿
What you taught for the 6 membered epoxide,is that correct?
Really good explanation. Thanks so mcuh for posting this!!! :D
perfect
wouldn't this occur as an SN1 reaction? if so, would the nucleophile come in concertedly as shown here?
Of course it would, but the guy expaining this reaction is clearly not familiar with the types of nucleophilic substitution.
Yeah, Khan academy is never right! Don't you hate it when you've been studying OChem for like 35 minutes and start realizing doctors are getting it all wrong!
note 1: Acid protonates epoxide to make --OH+--, then concerted mechanism happens...8 months later, you probably understand that by now, I hope.
note 2: The Khan academy goes to great lengths not to use jargon, or material you may not have reached yet. They explain things with simple building blocks, not showing off their knowledge like most arrogant instructors.