see, this is the point where most of the people are wrong because the main condition for aldol is not alpha-hydrogen but the acidity of the alpha hydrogen.

 

If you know the mechanism of aldol condensation then you'll know that in 1st step, the alpha hydrogen is withdrawn creating a carbanion which attacks on other molecules to proceed for aldol. As dilute NaOH is being used here & the alpha hydrogen is not acidic (in this question, due the presence of two methyl groups the alpha hydrogen will not be acidic) then OH^- ion will not be able to extract the alpha hydrogen & so, there will be no aldol. therefore, it will go for canizzaro....

 

In this question, A VERY STRONG BASE is required for aldol which against all odds can extract the alpha hydrogen...

 

i hope you get the concept...

 

 

Sorry,its mine ques;

Why skin burns on exposing with methylene chloride?

 

 

see, if you carefully observe the mechanism then you'll see that the very 1st step is the abstraction of alpha hydrogen by a strong base.

 

now, for the abstraction of the alpha hydrogen, the alpha hydrogen must be acidic else it will not be abstracted.

 

in the question given by you, the alpha carbon has 2 methly groups attached to it, so, the methyl groups are giving their +I effect thereby decreasing the acidity of the alpha hydrogen.

 

now, since the alpha hydrogen is no more acidic then the OH^- ion will act as a nucleophile rather than a base & so, there will be attack of OH^- as a nucleophile & the reaction will proceed for canizzaro.

 

I hope you get the concept...