Question

3-hydroxybutanal can be formed by the reaction of: A. methanol in diethyl ether. B. ethanal in base, then in acid. C. butanal in strong acid. D. methanal and ethanal in catalytic base.

Short answer

B. ethanal in base, then in acid.

Step-by-step solution

- Understand the Reaction

Identify the process needed to obtain 3-hydroxybutanal. This molecule can commonly be formed through an aldol reaction.

- Eliminate Unlikely Options

Methanol in diethyl ether (Option A) and butanal in strong acid (Option C) do not align with typical aldol reaction conditions, so these can be dismissed.

- Evaluate Remaining Options

Option B suggests ethanal in base followed by acid. Option D suggests methanal and ethanal in catalytic base. Both involve reactions which can form 3-hydroxybutanal.

- Determine the Correct Mechanism

An aldol reaction between ethanal (acetaldehyde) molecules (Option B) using base will initially lead to an aldol product (3-hydroxybutanal) and acid will complete the reaction.

- Confirm the Correct Answer

Methanal and ethanal in catalytic base (Option D) might lead to a cross-aldol product but doesn't describe the process as neatly as Option B.

Key concepts

Understanding Organic Chemistry

Organic chemistry is all about studying carbon-containing compounds and their reactions. You'll come across many different molecules and reactions. An important reaction in organic chemistry is the **aldol reaction**. It involves two molecules combining to form a larger one with a new carbon-carbon bond. This reaction is special because it creates both an alcohol (hydroxy group) and an aldehyde/ketone group in the same molecule. Knowing how these reactions work helps us understand how complex molecules are built in both laboratories and living organisms.

Reaction Mechanisms in Aldol Reactions

Reaction mechanisms show the step-by-step process of how reactants transform into products. The aldol reaction follows a specific mechanism:

• First, a base (like hydroxide) deprotonates an aldehyde to form an enolate ion.
• This enolate ion acts as a nucleophile, attacking another aldehyde molecule.
• The result is a new carbon-carbon bond, giving us a β-hydroxyaldehyde or β-hydroxyketone.
• A subsequent acid step can further transform this product, but in simpler cases, it's the alcohol and aldehyde functional groups that we notice.

It's fascinating how just understanding a few steps can explain the formation of complex molecules!

Formation of 3-Hydroxybutanal

3-Hydroxybutanal is an example of a hydroxyaldehyde formed by an aldol reaction. In our exercise, we're looking at how to form 3-hydroxybutanal specifically. The right conditions for this involve reacting two **ethanal (acetaldehyde) molecules in the presence of a base.**

• The base deprotonates one acetaldehyde, forming an enolate ion.
• This enolate ion nucleophilically attacks another acetaldehyde molecule.
• We end up with 3-hydroxybutanal after acid workup if required.

Understanding this mechanism helps in visualizing how hydroxyaldehydes like 3-hydroxybutanal form and why certain conditions (like using base) are essential for the reaction.