Aldol condensation | Alpha Carbon Chemistry | Organic chemistry | Khan Academy

Base-catalyzed mechanism for aldol addition and aldol condensation. Created by Jay.
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[@j.a.7047]

Hey everyone, just to clarify, -OH is a good leaving group in this situation. It does not get converted to H2O.

[@DonotWorryIAmHere]

Only constructive criticism: He should've shown the protonation of the -OH group before it left! ( -OH "hydroxide" is a TERRIBLE LEAVING GROUP) other than that, thanks for the brilliant clarification! -cheers!

[@hansenyang4014]

No that is incorrect. This reaction is done in basic conditions so the OH group cannot be protonated. The reaction is done in NaOH so the OH group can leave without much difficulty and reinforce the alkaline nature of the solution. I know this comment was made six years ago but I hope this clarifies the same question for future viewers.

[@kamh]

The reason why the OH group can leave is because the reaction proceeds via an E1CB where CB means conjugate base. The protons on the alpha carbons ie the ones that are adjacent to the carbonyl are relatively acidic and so can be deprotonated by a weak base. This results in the enolate anion to form which is a relatively stable conjugate base. although this anion is stable it still prefers to lose an OH group ( Due thermodynamic stability reasons) and so the oxygen on the enolate ion collapses back which kicks of the adjacent double bond which then subsequently kicks off the OH group. Hope this helps.

[@grant4360]

Where does the initial OH- come from if it is introduced in solution as NaOH, then how does it break apart and retain its charge?

[@visheshjain1999]

-OH is not a good leaving group,thats why we make it -OH2+ and then make it leave,but at 6:10 ,you made -OH leave,how?

[@Yashpandey467]

Vishesh Jain because it's already a highly basic medium and so (oh-) becomes a strong leaving group

[@katp9116]

Can you actually explain this a little further, or lets say, dumb this down a little?

[@TheAttacker96]

the reason the -oh is able to leave even though it is a bad LG is because having the molecule become conjugated is a lot more stable. the stability from having a conjugated molecule allows the oh to leave

[@tunneltrance]

its base catalyzed so it has to reform at the end somehow

[@shinn-tyanwu4155]

Very informative 😊

[@zahrashahabinezhad]

Why can't OH be removed from the aldol before the deprotonation?

[@bonbonpony]

Because -OH groups are not good leaving groups normally. (Otherwise, alcohols would be rather unstable :q ) The bond between the oxygen and carbon is pretty strong. Protonation makes it a better leaving group because it gives the oxygen more positive charge, and it doesn't pull the electrons so strong towards itself anymore. They are pushed away more closer to the carbon, and if you give them a little more nudge, they can go there and stay there, breaking the bond between the carbon and the oxygen.

[@kristinaf.2648]

Could somebody verify, (English is my third language) the aldol consendation is always as a two step mechanism to view at? First step, aldol addition then the actual consendation?

[@bonbonpony]

Yes, the condensation is like an extra step. The reaction is allowed to go further when there's more heat.

[@renilkumarak6406]

Thanks :')

[@katp9116]

Hey, So does the -OH group get protonated before it leaves or no? Some people (in the comments) are saying yes and some are saying no. If it doesn't, can you explain why not?

[@hansenyang4014]

No that is incorrect. This reaction is done in basic conditions so the OH group cannot be protonated. The reaction is done in NaOH so the OH group can leave without much difficulty and reinforce the alkaline nature of the solution. I know this comment was made six years ago but I hope this clarifies the same question for future viewers.

[@bonbonpony]

What does the heat change in this picture so that the reaction can proceed further than without it?

[@zarazainab9871]

THANKYOU SIRRRR

[@ghadeer5049]

gorgeous 😍 Thank you 🌸

[@saumyatrivedi373]

video is really awesome. thanks man!

[@asheearif8990]

Uhhh gooosshhhh what the hellll... m still in this confusion what is the difference b/w aldol reaction and aldol condensation

[@jcmick8430]

Reaction refers to the enolate condensation when we form pi bond

[@kevinsolomon6742]

Lightning fast.

[@martinofgliwice1486]

May I synthesise 2,6-dimethylhex-2-enone from 5-oxo-4-methylheptanal via intramolecular aldol condensation?

[@thelabadabada]

Why is it called a condensation reaction ? whe is the elimination of water ?

[@fionaWhatever]

thelabadabada Well you have a OH- leaving group plus the Proton taken by the base, so technically H2O is eliminated

[@aslinvazqueznieves2986]

Because what leaves is H, not water. When we eliminate water from a molecule, the OH is first protonated and then leaves in the form of water. Here, an eternal OH molecule captures de H, so the thing leaving the molecule is an H, but when the Leaving H combines with the molecule that took it (OH) it produces water

[@dr.abeyweera6819]

Can you explain the conversion of 1 octen 3 one to 1 octen 3 ol

[@MyDragon98]

city off ba

[@helihel1323]

Why you explain so fast just ?!!!!!

[@041-garimasaraswat5]

Garima saraswat roll no 41 secA