Certain Aldehydes, ketone and certain alcohol undergo iodoform test. Certain Aldehydes, ketones undergo aldol condensation. While certain aldehydes undergo Cannizaro's reaction. Aldehydes responds to tollen reagent and fehling reagent test.

Which of the following will respond to both Tollen's reagent and Fehling test?

Ethanal

The correct answer is option 2. Ethanal.

Both Tollens' test and Fehling's test are used in organic chemistry to identify the presence of aldehydes. They achieve this by exploiting the reactivity of the aldehyde functional group (R-CHO) towards oxidation. Let's delve deeper into how these tests work and why they don't react with other options you provided.

1. Tollens' Reagent and Test:

Reagent: Ammoniacal silver nitrate (\(AgNO_3\) solution with ammonia)

Reaction: When Tollens' reagent comes in contact with an aldehyde, the aldehyde undergoes oxidation. The aldehyde's carbonyl group \((C=O)\) is oxidized to a carboxylic acid \((R-COOH)\), while the silver ions \((Ag^+)\) from the reagent are reduced to elemental silver \((Ag)\). This elemental silver precipitates as a shiny metallic mirror on the inner surface of the test tube, indicating a positive test.

2. Fehling's Test:

Reagent: A mixture of Fehling's solution A (copper sulfate solution) and Fehling's solution B (potassium sodium tartrate solution)

Reaction: Similar to Tollens' test, Fehling's test also involves the oxidation of the aldehyde. The aldehyde's carbonyl group is oxidized to a carboxylic acid, and the cupric ions \((Cu^{2+})\) from Fehling's solution A are reduced to cuprous ions \((Cu^+\). This reduction is accompanied by a color change from the characteristic blue color of the cupric complex to a red precipitate of cuprous oxide \((Cu_2O)\), signifying a positive test.

Why these tests don't work for other options:

Benzaldehyde: Although an aldehyde, benzaldehyde is an aromatic aldehyde. Aromatic rings can sometimes hinder the reactivity of the carbonyl group. While it reacts with Tollens' test, it might not readily react with Fehling's test due to this reduced reactivity.

Acetone and Acetophenone: These are both ketones \((R-CO-R')\). Ketones have a similar carbonyl group \((C=O)\) as aldehydes, but with two large carbon groups on either side instead of a hydrogen in aldehydes. This difference in structure makes ketones generally less reactive towards oxidation. Consequently, they won't react with either Tollens' or Fehling's test.

In conclusion, Tollens' test and Fehling's test are valuable tools for identifying aldehydes based on their characteristic reactivity towards oxidation. Their ability to differentiate aldehydes from ketones and other functional groups makes them crucial in organic chemistry analysis.