https://preview.redd.it/ngyfez8a7aa81.png?width=247&format=png&auto=webp&s=e7a32c6d93b1176ba88a17ed025b76edb6c151f9
on the german wikipedia page for the Horner-Wadsworth-Emmons-Reaction it is stated that the phosphonate stabilized carbanion is a stronger nucleophile but a weaker base relative to the ylid in the wittig reaction. how can that be? i thought that stronger nucleophile automatically means also a stronger base...
Carbonyl Umpolung is a powerful strategy in organic chemistry to construct complex molecules. Over the last years, versatile catalytic approaches for the generation of acyl anion equivalents from carbonyls have been developed, but methods to obtain alkyl carbanions from carbonyls in a catalytic fashions are still at an early stage. This Minireview summarizes recent progress in the generation of alkyl carbanions through catalytic carbonyl Umpolung. Two different catalytic approaches can be utilized to enable alkyl carbanion generation from carbonyl compounds: the catalytic Wolff Kishner reaction and the catalytic single‐electron reduction of carbonyls and imines. We discuss the reaction scope, mechanistic insights, and synthetic applications of the methods as well as potential future developments.
https://ift.tt/3foxAfK
In the allylic carbanion, I assume this is the case as the lone pair is delocalize. For the carbocation, I think the + charged carbon still has a p-orbital which it can use to interact with the other two p-orbitals, even thought it has no electrons in it. Is this true? Are both of the structures below conjugated?
https://preview.redd.it/j4klcz1hkqc61.jpg?width=246&format=pjpg&auto=webp&s=2743aef660d7efd74092c67a9c3ca9788bd99d24
Hi r/chemistry
I have a reaction that involves a carbanion reacting with a carbonyl to give an alcohol. The reaction seems to work extremely well if the carbanion is generated with a potassium base (KHMDS and KOtBu work 100% conversion) but not at all with a lithium base (LiOtBu, LiHMDS, LDA, didnt work, starting material recovered). Sodium is in between. I'm having trouble explaining this.
I estimate that the pKa of my carbon is about 16. The reaction is done in THF at -78. The nature of the carbonyl doesn't make much difference as long as its an aldehyde or a ketone.
If anyone has come across this sort of thing before please let me know you could save me a lot of work.
Journal of the American Chemical SocietyDOI: 10.1021/jacs.9b11944
https://ift.tt/2Ro9lU5
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c00629
https://ift.tt/3ceHbm9
Nature Chemistry, Published online: 03 February 2020; doi:10.1038/s41557-019-0412-9
Although methods exist for the construction of CF3-containing stereocentres, the utilization of α-trifluoromethyl carbanions remains challenging because of the propensity for fluoride elimination. A strategy has now been developed to stabilize these carbanions through a neighbouring cationic Pd complex and the corresponding Pd-stabilized zwitterions participate in asymmetric cycloadditions with a broad range of acceptors.
https://ift.tt/2Ul1gBD
Journal of the American Chemical SocietyDOI: 10.1021/jacs.9b12053
https://ift.tt/2TUZG9e
My notes explained that a if it has a trigonal planar shape then the inter-electronic repulsion would be too great due to the presence of three 90 degrees lone pair bond pair repulsion. However, if it had a trigonal planar structure wouldn't the lone pair be in a p orbital so it has a dumbbell shape with the 2 lobes above and below the 3 trigonal planar bonds. So wouldn't the repulsions from the lone pair-bond pair cancel out from above and beneath?
I drew this image to represent what i mean visually http://imgur.com/Sr5h2iR The arrows denote the repulsions between the top lope and the bonds and the bottom lope and the bonds. So shouldn't those repulsions be equal such that the repulsions that are to be concerned are only the bond pair-bond pair repulsions? If so then the shape should be trigonal planar which is not true. This would also mean that similar structures should have a trigonal planar structure which again is not true.
I understand why carbocations are stabilized by more substitution, but I don't see why carbanions don't follow the same stabilization rule.
Hi there, I am working on a practice exam and a question has come up about carbanion stability.
Which is more stable, a benzene ring with a lonepair on one of the carbons or 1-propyne (CH3-C=[triple bond]=C:)
My guess is that the benzene is more stable as its a 2* carbon and resonance can add to the stability, however I dont know enough to rule out 1-propyne and would love a second opinion.
So, I have a decent amount of organic chemistry background for an undergrad, but I've discovered something I'm not really sure about.
How do we determine the hybridization of carbanions?
Say we deprotonated acetylene. The lone pair would have to be in an sp orbital because the carbon is sp hybridized and has two pi bonds, using up the available p orbitals.
But what if we deprotonated ethane? What would the hybridization of the carbanion be? Would it be sp3 and tetrahedral to keep the lone pair as far from the bonds as possible, or would it be sp2 and planar like a carbocation?
I did a bit of googling and didn't really find any definitive answers either way, so if any of you could explain this a bit, that would be awesome!
Thanks!
I'm trying to predict a product, and though the electron accepting carbon of the carbonyl would stabilize the produced carbanion I believe resonance provided from a benzyllic carbanion results in a more stable molecule and thus would be present in the propagating species. Am I mistaken?
This review presents a survey of recent examples of fragment coupling reactions that form carbon–carbon bonds via carbanionic or free radical intermediates in total synthesis. The aim is to identify extensible lessons from each example that might be useful to students in the field. Powerful advances in the generation and application of carbanionic and free radical intermediates in complex settings are highlighted.
Abstract
Fragment coupling reactions that form carbon–carbon bonds are valuable transformations in synthetic design. Advances in metal‐catalyzed cross‐coupling reactions in the early 2000s brought a high level of predictability and reliability to carbon–carbon bond constructions involving the union of unsaturated fragments. By comparison, recent years have witnessed an increase in fragment couplings proceeding via carbanionic and open‐shell (free radical) intermediates. The latter has been driven by advances in methods to generate and utilize carbon‐centered radicals under mild conditions. In this Review, we survey a selection of recent syntheses that have implemented carbanion‐ or radical‐based fragment couplings to form carbon–carbon bonds. We aim to highlight the strategic value of these disconnections in their respective settings and to identify extensible lessons from each example that might be instructive to students.
https://ift.tt/2ZsQVnX
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c01722
Yun Xiong, Dandan Chen, Shenglai Yao, Jun Zhu, Ales Ruzicka, and Matthias Driess
https://ift.tt/32grzvC
Installation of a carbanionic substituent, that is strongly stabilised by two (trifluoromethyl)sulfonyl (Tf = SO 2 CF 3 ) groups, into several fluorescence dyes including boron‐dipyrromethenes (BODIPYs), fluoresceins, and aminocoumarins has been achieved by the 2,2‐bis(triflyl)ethylation reaction of the dye frameworks with highly electrophilic Tf 2 C=CH 2 , followed by neutralisation with NaHCO 3 . Despite the contradiction between water‐solubility and lipophilicity, the carbanion‐decorated dyes thus obtained showed significant enhancement of not only water‐solubility but also lipophilicity. This work clearly demonstrates that the fluorinated, highly stabilised carbanionic substituent is a new option for controlling the macroscopic property of chemical materials.
https://ift.tt/2VdJDmA
I don't want to step on anybody's toes here, but the amount of non-dad jokes here in this subreddit really annoys me. First of all, dad jokes CAN be NSFW, it clearly says so in the sub rules. Secondly, it doesn't automatically make it a dad joke if it's from a conversation between you and your child. Most importantly, the jokes that your CHILDREN tell YOU are not dad jokes. The point of a dad joke is that it's so cheesy only a dad who's trying to be funny would make such a joke. That's it. They are stupid plays on words, lame puns and so on. There has to be a clever pun or wordplay for it to be considered a dad joke.
Again, to all the fellow dads, I apologise if I'm sounding too harsh. But I just needed to get it off my chest.
Do your worst!
I'm surprised it hasn't decade.
They were cooked in Greece.
For context I'm a Refuse Driver (Garbage man) & today I was on food waste. After I'd tipped I was checking the wagon for any defects when I spotted a lone pea balanced on the lifts.
I said "hey look, an escaPEA"
No one near me but it didn't half make me laugh for a good hour or so!
Edit: I can't believe how much this has blown up. Thank you everyone I've had a blast reading through the replies 😂
It really does, I swear!
Because she wanted to see the task manager.
Heard they've been doing some shady business.
but then I remembered it was ground this morning.
Edit: Thank you guys for the awards, they're much nicer than the cardboard sleeve I've been using and reassures me that my jokes aren't stale
Edit 2: I have already been made aware that Men In Black 3 has told a version of this joke before. If the joke is not new to you, please enjoy any of the single origin puns in the comments
They’re on standbi
This review presents a survey of recent examples of fragment coupling reactions that form carbon–carbon bonds via carbanionic or free radical intermediates in total synthesis. The aim is to identify extensible lessons from each example that might be useful to students in the field. Powerful advances in the generation and application of carbanionic and free radical intermediates in complex settings are highlighted.
Abstract
Fragment coupling reactions that form carbon–carbon bonds are valuable transformations in synthetic design. Advances in metal‐catalyzed cross‐coupling reactions in the early 2000s brought a high level of predictability and reliability to carbon–carbon bond constructions involving the union of unsaturated fragments. By comparison, recent years have witnessed an increase in fragment couplings proceeding via carbanionic and open‐shell (free radical) intermediates. The latter has been driven by advances in methods to generate and utilize carbon‐centered radicals under mild conditions. In this Review, we survey a selection of recent syntheses that have implemented carbanion‐ or radical‐based fragment couplings to form carbon–carbon bonds. We aim to highlight the strategic value of these disconnections in their respective settings and to identify extensible lessons from each example that might be instructive to students.
https://ift.tt/2ZsQVnX
