Question

How many products are possible when ethanal and phenyl ethanal (mixture) is treated with dil. \(\mathrm{NaOH}\) at about \(10^{\circ} \mathrm{C}\).

Short answer

4 products.

Step-by-step solution

Identify the Aldol Reaction Participants

Ethanal (acetaldehyde) and phenyl ethanal (phenylacetaldehyde) both have an alpha-hydrogen that makes them candidates for aldol condensation in the presence of a base like dilute NaOH.

Consider Self-condensation

Evaluate each aldehyde for self-condensation. Ethanal can react with itself to form 3-hydroxybutanal. Similarly, phenyl ethanal can form a similar compound by reacting with itself, yielding a 3-hydroxy product, phenylpropanal.

Consider Cross-condensation

Next, consider the cross-condensation between ethanal and phenyl ethanal. Ethanal can act as a nucleophile to attack phenyl ethanal's carbonyl carbon, forming a cross aldol product. Similarly, phenyl ethanal can attack the carbonyl carbon of ethanal, producing another aldol product.

Enumerate the Possible Products

Combine the self-condensation and cross-condensation products. From step 2, you have two products: one from the self-condensation of ethanal, and one from the self-condensation of phenyl ethanal. From step 3, you have two products from cross reactions: ethanal reacting with phenyl ethanal and vice versa.

Count the Total Products

Count all unique aldol products resulting from both self and cross-condensations. There are two self-condensation products and two cross-condensation products. Thus, there are a total of four different products.

Key concepts

Self-condensation

Self-condensation is an intriguing reaction in organic chemistry, particularly in the context of aldol reactions. It occurs when a single molecule, which contains an alpha-hydrogen atom, reacts with itself rather than with another type of molecule.
For example, in the reaction between ethanal molecules, each molecule has an alpha-hydrogen that allows it to participate in self-condensation. This reaction is catalyzed by a base, like dilute \(\mathrm{NaOH}\), which deprotonates the alpha-hydrogen, leading the molecule to form an enolate ion.
This enolate ion acts as a nucleophile, attacking the carbonyl carbon of a neighboring ethanal molecule. This nucleophilic attack generates a beta-hydroxy aldehyde, such as 3-hydroxybutanal, which can further dehydrate to produce an unsaturated aldehyde.
Self-condensation is important as it helps in forming complex organic molecules from simpler ones, setting the stage for more advanced chemical transformations.

Cross-condensation

Cross-condensation, also known as mixed aldol condensation, involves two different carbonyl-containing molecules, each possessing alpha-hydrogens, participating in the reaction. The process results in a new product that contains structural elements of both reactants.
In the case of ethanal and phenyl ethanal, cross-condensation involves one molecule acting as the nucleophile while the other acts as the electrophile.

• The enolate ion from ethanal can attack the carbonyl group of phenyl ethanal, forming a unique aldol product.
• Conversely, phenyl ethanal can generate an enolate ion, which will then attack the carbonyl carbon of an ethanal molecule, yielding another distinct aldol product.

This type of condensation is essential for synthesizing diverse molecular architectures and can be controlled to favor the production of specific desired compounds. Each resultant product from cross-condensation contains features from both starting materials, reflecting the integrated nature of their chemical structures.

Organic Chemistry Reactions

Organic chemistry is rich with a variety of reactions that allow the transformation of simple molecules into complex structures. Aldol condensation is a prime example, representing a fundamental mechanism by which organic chemists build larger molecules from smaller building blocks.

• These reactions typically involve nucleophiles and electrophiles interacting through carbon-carbon bond formation.
• The presence of specific functional groups, like carbonyl groups, plays a critical role in guiding these reactions.
• Such transformations are often catalyzed by bases or acids, facilitating the necessary electronic rearrangements for bond formation.

Understanding these reactions provides insight into synthetic pathways used in creating a wide range of useful compounds, spanning medicines, plastics, and even natural products. Mastery of these concepts opens the door to innovative developments in chemistry and related fields.