Question

One of the following aldehydes undergoes Cannizzaro’s reaction and reduces the Schiff’s reagent, but does not reduce Fehling’s reagent. That is

• A. 2-OH-PhCHO
• B. PhCHO
• C. HCHO
• D. CH3CHO

Answer 1

The Correct Option is B

Cannizzaro's reaction is observed for aldehydes that lack an alpha-hydrogen. This means that the aldehyde cannot form an enolate ion and undergo aldol condensation. Instead, it undergoes disproportionation (Cannizzaro's reaction).
Now, Schiff's reagent is used to test for the presence of aldehydes, and all aldehydes generally reduce Schiff's reagent.  
Fehling's reagent specifically tests for the presence of reducing sugars and aliphatic aldehydes but does not respond to aromatic aldehydes. 
Given the options: 
1. \((2-OH-PhCHO)\): This is salicylaldehyde (an aromatic aldehyde with a hydroxyl group). 
2. \((PhCHO)\): This is benzaldehyde (a simple aromatic aldehyde). 
3. \((HCHO)\): This is formaldehyde. 
4. \((CH_3CHO)\): This is acetaldehyde. 
Among the options, benzaldehyde (PhCHO) is the one that: 
- Undergoes Cannizzaro's reaction because it doesn't have an alpha-hydrogen. 
- Reduces Schiff's reagent since it's an aldehyde. 
- Does not reduce Fehling's reagent because it's an aromatic aldehyde. 
So, the correct answer is: B. PhCHO (benzaldehyde)