In which reaction there is no need of alpha hydrogen?

In which reaction there is no need of alpha hydrogen?

In case of benzaldehyde the alpha carbon atom has no hydrogen atoms attached hence there is no alpha hydrogen present in benzaldehyde. Due to the absence of alpha hydrogen it also cannot undergo aldol condensation.

Which of the following aldehyde contain alpha carbon atom but not having alpha hydrogen atom?

Which of the following aldehydes contains alpha-C atom but does not have any alpha-H atom? Furfural, does not have an α-H atom but contains an α-carbon atom.

When two aldehydes without a hydrogen undergo Disportionation make carboxylic acid and alcohol?

Cannizzaro reaction
* The disproportionation reaction of aldehydes without α-hydrogens in presence of a strong base to furnish an alcohol and a carboxylic acid is called Cannizzaro reaction. One molecule of aldehyde is reduced to the corresponding alcohol, while a second one is oxidized to the carboxylic acid.

Why is the alpha carbon important?

The α-carbon is important for enol- and enolate-based carbonyl chemistry as well. Chemical transformations affected by the conversion to either an enolate or an enol, in general, lead to the α-carbon acting as a nucleophile, becoming, for example, alkylated in the presence of primary haloalkane.

What is alpha hydrogen in aldehydes?

The α-hydrogen atom is one that binds to a carbon alongside some functional group, e.g. ketone or an aldehyde group. Without this bonding, no hydrogen can be isolated by the process of Enolization. The hydrogen atoms in the alpha carbon atoms are known as alpha hydrogen.

Why is alpha hydrogen necessary for aldol condensation reaction?

On mixing with dilute acid or base (aqueous), aldehydes containing α-hydrogen can react with themselves thereby resulting in the formation of β‐hydroxy aldehyde compounds or aldol compounds. This is because the resulting compound will have a functional group, aldehyde, and alcohol.

Which of the following aldehyde is present as gas?

Which of the following aldehyde is present as gas? Explanation: Methanal is a gas (boiling point -21°C), and ethanal has a boiling point of +21°C. That means that ethanal boils at close to room temperature. The other aldehydes and the ketones are liquids, with boiling points rising as the molecules get bigger.

What happens if there are no alpha hydrogenated aldehydes?

If there are no alpha hydrogens, there can be no enolate and thus no aldol. The only possibility is nucleophilic attack on the aldehyde carbonyl. In this situation the much less favourable hydride transfer can occur. Why do alpha hydrogenated aldehydes not undergo the Cannizzaro reaction?

Why do aldehydes with just one alpha-H prefer aldol over Cannizzaro?

Verdict: Aldehydes with just one alpha-H do not prefer Aldol; they rather proceed to Cannizzaro. Referring to Jans answer one might ask for a reason that in the case of 2-methyl-propanal the canizzaro reaction gets favoured over the aldol reaction in comparison to other α -deprotonizable aldehydes.

When does the Cannizaro reaction occur?

The Cannizaro reaction occurs when there is no other easy reaction pathway. Aldehydes WITH alpha hydrogens are very prone to enolisation and then aldol condensation. This is the usual pathway. If there are no alpha hydrogens, there can be no enolate and thus no aldol.

Why does chloral give Cannizzaro reaction but not alpha hydrogen?

Chloral does not give Cannizzaro reaction even it doesn’t have alpha hydrogen, but gives haloform instead. It is because in chloral there is a potential leaving group (good leaving group) i.e CCl3- since it’s weak base. So in this reaction when we use OH- that OH- attack on alpha carbon and CCl3- leaves to give chloroform as product.