aldol or canizarro ?

btw any more exceptions ..plz add here

Shabaash Varkha...I didn't know it's there in solomons...somebody tell Mr/Ms/?? Vivek.

Had a sudden thought...could Mr/Ms/None Vivek's explanation be overcome by hyperconjugation?
2 methyl groups = 3 x 2 hyperconjugative structures = 6

1 methyl and 1 ethyl group would provide lesser HC effect(for asish).

There is nothing else I could think of, because hyperconjugation can override resonance.

@everyone: pls see post#14

Aldol condensation is much faster than canizzaro's reaction for obvious reasons..... And so aldol condensation would predominate...
AND for all those who said that the carbanion will be destablised by inductive effect, here is a firm reminder that the dispersion of the negative charge will take place through the carbonyl carbon which will compensate more than twice that of the the destabilisation by inductive effect.....

Always remember resonance effect is much much stronger than inductive effect
There is(are) exception(s)..... Can you tell me where????
Its in the case of halogens....

CAN ANY ONE TELL ME IF THE SAME COMPOUND HAS \alpha- H ON ONE SIDE AND NOT ON OTHER THAN WAT WILL BE THE REACTION ALDOL OR CANIZZARO OR BOTH????[7][7][7]

but then if i remember ....

there was a question in NCERT..

whether 2-methyl pentanal or 2-methyl butanal gives aldol or cannizarro, the answer was given ALDOL..

Here, steric effect not applicable??

or do we disregard NCERT in this question?? (IIT follows NCERT or other books ??)

well there can be infinitely many exceptions...

the reason why carbonyl compounds containing α- hydrogen do not undergo cannizaro is they enolise so if the enolate formed by the compund isnt stable enough or is too crowded to be attacked...

there will be some disproportionation.

hmmm will have to think of some specific examples....

aldol because reactant has alpha - H atom.

thx everyone [1]

Aldol addition's first step is an equilibrium step, the loss of proton. Due to steric effects the equilibrium will shift largely backwards and Cannizzaro will be favoured instead.

Here v have both, the alpha-H as well as one with the -methyl group...(Also, the conc. of base aint mentioned), so v can opt fr both the reac.n(s).

But if aldol occurs, the C ^- formed wud be destabilised by the +I of methyl, hence carbanion won't be stable, as govind already pointed out.....Isliye we wud prefer CanniZ.

@avik how cannizzaro is favored????

for cannizzaro reaction \alpha hydrohen must be absent but present here so preferred shoul be aldol na......[7][7]

Yes...both will occur, but Cannizzaro product will dominate, as Cannizzaro is favoured.

I think it depends on the concentration of the base...at 50% conc. of base Canninzaro reaction and at low concentration Aldol reaction...but in this case since the carbonion formed at α position will be destabilised by inductive effect of 2 methyl grps...so i go with Canninzarro reaction..