Saved Bookmarks
| 1. |
Benzaldehyde reduces Tollens' reagent but not the Fehling's or the Benedict's solution. Explain. |
| Answer» Solution :The electron-donating resonance effect (+R-effect) of the benzene ring increases the electron density in the carbonly group of benzaldehyde. This, in turn, increases the electron density in the C-H bond of the aldehyde group. As a result, the C-H bond becomes STRONGER and hence only stronger oxidising agents like Tollens' reagent, `Ag(NH_(3))_(2)^(+)(E_(Ag^(+)//Ag)^(@)=+0.80V)` can oxidise C-H to C-OH toform carboxylic Acids but weaker oxidisinig agents like FEHLING's solution (`Cu^(2+)+` tartrate ion +base) and Benedict (`Cu^(2+)` + CITRATE ion+Base) solution `(E_(Cu^(2+)//Cu^(+))^(@)=0.18V)` fail to oxidise benzaldehyde to benzoic acid . Thus, in general, all these three reagents oxidise aliphatic aldehydes but only tollens' reagent oxidise aromatic aldehydes. | |