Question

Which of the following compounds will give methyl vinyl ketone by aldol condensation followed by dehydration? (a) Formaldehyde and acetaldehyde (b) Formaldehyde and acetone (c) Acetaldehyde and acetone (d) Two molecules of acetaldehyde

Short answer

Answer: (b) Formaldehyde and Acetone.

Step-by-step solution

Understand Aldol Condensation and Dehydration reaction

Aldol condensation is an organic reaction in which an enolate ion reacts with an aldehyde or ketone to form a β-hydroxy aldehyde or β-hydroxy ketone. This reaction is then followed by dehydration, in which a molecule of water is removed, leading to the formation of an α,β-unsaturated aldehyde or ketone.

Write out the structures of the given compounds

We need to identify the structures for the given compounds: (a) Formaldehyde: H-CHO Acetaldehyde: CH3-CHO (b) Formaldehyde: H-CHO Acetone: CH3-CO-CH3 (c) Acetaldehyde: CH3-CHO Acetone: CH3-CO-CH3 (d) Two molecules of Acetaldehyde: CH3-CHO

Perform Aldol Condensation

Perform the aldol condensation reaction on each of the pairs and determine the resulting β-hydroxy aldehyde or β-hydroxy ketone product for each pair: (a) Formaldehyde (H-CHO) and Acetaldehyde (CH3-CHO) give CH3-CH(OH)-CH2-CHO (b) Formaldehyde (H-CHO) and Acetone (CH3-CO-CH3) give H-CH(OH)-CH2-CO-CH3 (c) Acetaldehyde (CH3-CHO) and Acetone (CH3-CO-CH3) give CH3-CH(OH)-CH2-CO-CH3 (d) Two molecules of Acetaldehyde(CH3-CHO) give CH3-CH(OH)-CH2-CHO

Perform Dehydration

Perform a dehydration reaction on each of the products obtained from step 3: (a) CH3-CH(OH)-CH2-CHO gives CH3-CH=CH-CHO (b) H-CH(OH)-CH2-CO-CH3 gives H-CH=CH-CO-CH3 (Methyl vinyl ketone) (c) CH3-CH(OH)-CH2-CO-CH3 gives CH3-CH=CH-CO-CH3 (d) CH3-CH(OH)-CH2-CHO gives CH3-CH=CH-CHO

Compare the products to Methyl Vinyl Ketone

Compare the products from step 4 to Methyl Vinyl Ketone (H-CH=CH-CO-CH3): (a) CH3-CH=CH-CHO is not equal to Methyl Vinyl Ketone (H-CH=CH-CO-CH3) (b) H-CH=CH-CO-CH3 is equal to Methyl Vinyl Ketone (H-CH=CH-CO-CH3) (c) CH3-CH=CH-CO-CH3 is not equal to Methyl Vinyl Ketone (H-CH=CH-CO-CH3) (d) CH3-CH=CH-CHO is not equal to Methyl Vinyl Ketone (H-CH=CH-CO-CH3) Hence, the correct answer is (b) Formaldehyde and Acetone.

Key concepts

Organic Chemistry

Organic chemistry is the fascinating study of the structure, properties, and reactions of carbon-containing compounds. Carbon atoms can form long chains, rings, and complex structures because of their unique ability to create stable bonds with themselves and other elements. This versatility makes organic chemistry a vast and diverse field. In organic chemistry, reactions like aldol condensation are common. These reactions are crucial in forming many natural and synthetic compounds. They involve the combination of smaller molecules to form more complex substances, often through specific mechanisms like nucleophilic attacks. Understanding these reactions helps scientists design molecules for pharmaceuticals, plastics, and many other materials.

Enolate Ion

The enolate ion is a pivotal intermediate in many organic reactions, including aldol condensation. It is formed when a ketone or an aldehyde with at least one alpha hydrogen is deprotonated at the alpha position, usually by a strong base. This ion is characterized by resonance, meaning the electrons can be delocalized between the oxygen and the alpha carbon. - **Formation**: The enolate ion is typically generated by deprotonating the alpha hydrogen using a strong base such as hydroxide or alkoxide. - **Stability**: Enolate ions are stabilized through resonance, allowing the negative charge to be shared between the oxygen and the carbon atom. The presence of an enolate ion is essential in aldol condensation, as it acts as a nucleophile. This means it has the ability to attack an electron-deficient carbon, like the carbonyl carbon in another molecule, leading to the formation of a new carbon-carbon bond.

Dehydration Reaction

A dehydration reaction is a chemical transformation in which a water molecule is removed from a compound. This type of reaction is a common follow-up in aldol condensations, playing a key role in forming more stable, conjugated systems like α,β-unsaturated carbonyl compounds. In the context of aldol condensation, after the initial formation of a β-hydroxy ketone or aldehyde, dehydration can occur:

• Occurs through the loss of a water molecule from the β-hydroxy compound.
• Facilitates the creation of a double bond between the alpha and beta carbons, forming an enone.

This step is crucial as it converts the aldol addition product into more stable and less reactive α,β-unsaturated compounds like methyl vinyl ketone, often resulting in improved reaction outcomes and material properties.

Methyl Vinyl Ketone

Methyl vinyl ketone (MVK) is an important unsaturated ketone in organic chemistry. It is characterized by the presence of a vinyl group (\[CH=CH_{2}\]) attached to the carbonyl (\[C=O\]) carbon, making it unsaturated. This specific structure gives MVK its characteristic reactivity and utility in various chemical applications.- **Reactivity**: MVK is highly reactive as both a Michael acceptor and in other nucleophilic addition reactions due to its α,β-unsaturated nature.- **Uses**: It is used in the synthesis of pharmaceuticals, fragrances, and as a precursor to other chemicals.Understanding the formation and reactivity of MVK is crucial in organic synthesis. In aldol condensations followed by dehydration, MVK can be produced, highlighting its role as a key building block in complex chemical production.