How do you account for the fact that the \(\alpha\) -hydrogens of an aldehyde (say, n-butyraldehyde) are much more acidic than any other hydrogens in the molecule?

Short Answer

Expert verified
The alpha hydrogens of an aldehyde, such as n-butyraldehyde (\( CH_3CH_2CH_2CHO \)), are more acidic than any other hydrogens in the molecule due to resonance stabilization and inductive effects. When an alpha hydrogen is removed, the resulting carbanion adjacent to the carbonyl group can be stabilized by resonance, forming an enolate ion with delocalized negative charge between the two oxygens. In contrast, removing a hydrogen from other carbon atoms in n-butyraldehyde results in a carbanion without resonance stabilization or inductive effects from electron-withdrawing groups. Therefore, the alpha hydrogens in aldehydes are more acidic due to the greater stability of the anions formed after their removal.

Step by step solution

01

Understand the structure of n-butyraldehyde

The formula of n-butyraldehyde is \( CH_3CH_2CH_2CHO \). Draw the structure and identify the alpha hydrogens. Alpha hydrogens are those connected to the carbon atom that is adjacent to the carbonyl carbon atom.
02

Compare acidities of hydrogens in the molecule

Acidity of a hydrogen atom is related to the stability of the anion formed after the hydrogen loses its proton as a hydronium ion. The more stable the anion, the more acidic the hydrogen. We need to remove a proton, one at a time, from different carbon atoms in the molecule and see which anion has more resonance stabilization and inductive effects.
03

Analyze the anion formed from alpha hydrogen loss

When we remove an alpha hydrogen from n-butyraldehyde, we produce a carbanion that is adjacent to the carbonyl group. This carbanion can be stabilized by resonance with the carbonyl group, leading to the formation of an enolate ion, in which the negative charge is delocalized between the two oxygens.
04

Analyze the anion formed from other hydrogens in n-butyraldehyde

When we remove a hydrogen from other carbon atoms of n-butyraldehyde, the resulting carbanion does not have any resonance stabilization due to its distance from the carbonyl group. Moreover, there are no electron-withdrawing groups nearby to stabilize the carbanion through inductive effects.
05

Compare the stability of the resulting anions

The anion formed after the removal of an alpha hydrogen from n-butyraldehyde has resonance stabilization and is more stable compared to the anion formed after the removal of other hydrogens. Due to this stability, alpha hydrogens in aldehydes are more acidic than other hydrogens in the molecule.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Study anywhere. Anytime. Across all devices.

Sign-up for free