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Cannizaro reaction is not given by Chloral HCHO 2-methylpropanal p-methoxybenzaldehyde The answers are 1,2 I have doubt in 3,4. Generally aldehydes without alphe hydrogen give cannizaro reaction. Please tell me the conditions this is violated.

Cannizaro reaction is not given by
  1. Chloral
  2. HCHO
  3. 2-methylpropanal
  4. p-methoxybenzaldehyde
The answers are 1,2
I have doubt in 3,4. Generally aldehydes without alphe hydrogen give cannizaro reaction. Please tell me the conditions this is violated.

Grade:12

12 Answers

Aarti Gupta
askIITians Faculty 300 Points
7 years ago
Canninzaro reaction is the characteristic of those aldehydes which do not contain alpha-hydrogen.Thus formaldehyde(HCHO),chloral(CC3CHO) and p-methoxybenzaldehyde will show this reaction as in all these compounds alpha-hydrogen is ansent. But 2-methylpropanal do not give Canninzaro reaction as alpha-hydrogen is persent in this compound.
Himaja
40 Points
7 years ago
But CCl3CHO does not undergo cannizaro reaction.
CCl3CHO +OH- = CHCl. But not cannizaro products.
The answers are chloral and p-methoxybenzaldehyde.
How can 2-methyl propanal ( alpha-H present) undergo this rxn? 
And why doesn’t paramethoxy benzaldehyde (alpha-H absent) give cannizaro rxn ? 
Aarti Gupta
askIITians Faculty 300 Points
7 years ago
Dear student canninzaro reaction is given by only those aldehydes in which alpha-hydrogen is absent.So formaldehyde(HCHO),chloral(CCl3CHO) and p-methoxy benzaldehyde all will give this reaction as in all these compounds alpha-hydrogen is absent.Now in the question you have asked that compound which do not give canninzaro reaction so according to that 2-methylpropanal is the only option which contains alpha-hydrogen so it is clear that it will not show canninzaro reaction.You have mentioned that chloral does not undergo this reaction.However it shows the canninzaro reaction.So please check your question again,as in the question you are asking the compound not showing the reaction.
Abhishek Singh
104 Points
7 years ago
RESPECTED, maam 
I think that chloral would not undergo cannizaro rxn., it will give haloform rxn.
Because when acetaldehyde is treated withCl2/NaOH for galoform rxn. it is a intermediate which then gives chloroform and formic acid.
So here also the products will be same
 
Ajinder Singh
24 Points
5 years ago
2 methyl propanal is one of the exceptions of the cannizaro reaction even if it does have alpha hydrogen on heating at 170-200 C it will show cannizaro reaction this is probably due to +I effect
Kevin Arnav Roshan
11 Points
5 years ago
Only 2-methyl propanal and chloral should be the answers .... i say this because Formaldehyde and p-methoxy benzaldehyde give it going by the same reason given above and in definition of cannizaro reaction .... speaking of chloral , it will undergo haloform reaction as the mechanistic pathway would favour that over cannizaro .... 2-methyl propanal does not give it as the negative charge developed on that tertiary carbon would be highly unstable and so it is not energetically favourable ..
Anjana Dewanjee
25 Points
5 years ago
Here all the 4 compounds (HCHO, chloral,2 methyl propanal nd p-methoxybenzaldehyde will give cannizzaro reaction. In 2 methyl propansl,though alpha hydrogen is absent it will give cannizzaro reaction. It is an exceptional case
Abhishek Singh
104 Points
5 years ago
 
 chloral would not undergo cannizaro rxn., it will give haloform rxn which is similar to Cannizaro reaction but not Cannizaro.
When acetaldehyde is treated withCl2/NaOH for Haloform rxn. chloral  is a intermediate which then gives chloroform and formic acid.
So it will not give cannizaro
 
So here also the products will be same
deepansu
13 Points
4 years ago
Electronegative groups such as halogens destabilize carbocations by -I effect and hence hydration is more favorable.. So choral won`t show Cannizaro
Manoj
11 Points
4 years ago
Chloral don`t give cannizaro reaction as it undergo haloform reaction in strong alkali. 2-methyl propanal, having alpha hydrogen, gives cannizaro reaction due to +I -effect.
Rajat
15 Points
3 years ago
-CCl3 will have high -I effect so -OH will attack on CCl3 and not on -CHO to proceed cannizarro , chloroform can't give cannizarro products. 
 
 
 
                -BD
Rishi Sharma
askIITians Faculty 646 Points
one year ago
Dear Student,
Please find below the solution to your problem.

Chloral don`t give cannizaro reaction as it undergo haloform reaction in strong alkali. 2-methyl propanal, having alpha hydrogen, gives cannizaro reaction due to +I -effect.

Thanks and Regards

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