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42 lessons,
7h 3m
Directed Aldol - 2
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This is a type of directed Aldol in which cross product is the only product. It is important from exam point of view and a must watch!

Ankita Chowdhury
Student at DTU (Previously DCE); Chemistry lover; Passionate about teaching; @educator.ankita (Instagram) ; Let's make learning fun! :D

Unacademy user
Great to learn.I recommend it.
ma'am in the reaction vessel LDA or NaNH2 will be present at the time of adding the other carbonyl.. Cant LDA form it's enolate which will give another self aldol product.
Hi Aksh! LDA is a strong base but, due to steric hinderance at the electron-rich nitrogen atom caused by the bulky isopropyl groups, a very weak nucleophile. hence it is unable to form it's own enolate to give another self Aldol product. hope this helps. happy learning :)
Aksh Rajput
a year ago
ma'am I think you didn't understand my question.. my question is that when the other carbonyl compound is added , can't LDA form enolate of that compound which is added later and which in turn can react on another unenolised molecule of its own to give self aldol product..
Aksh the reason we are calling this as directed Aldol is because we are deciding that cross product should be major. What LDA is basically doing is that it is abstracting the alpha hydrogen from each and every pure carbonyl compound within the reaction vessel. After that when we are introducing another different carbonyl compound into the reaction vessel (by choice), we are finally getting the cross product as major product. But if you want to keep the same pure carbonyl in the reaction vessel and then treat it with LDA and finally introduce more molecules of that very carbonyl compound, then obviously self Aldol is the only option left. But this can't happen that you have one type of carbonyl compound in the reaction vessel with LDA already present in the reaction vessel and then you are adding another type of carbonyl compound into the reaction vessel and enolate ion is formed of that newly introduced carbonyl and then the self Aldol would take place. Why this won't happen is because you already have the enolate ions of the original pure carbonyl compound present in the reaction vessel ready to form cross Aldol product with the newly introduced carbonyl molecules.
Aksh Rajput
a year ago
okay thanks ma'am
Aksh Rajput
a year ago
okay thanks ma'am
ma'am can't an enolate react on another enolate followed by gaining an H+.
Nice. Informative as always