Name the reaction when a mixture of acetaldehyde and propanal is treated with aqueoous alkali solution.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Cross Aldol Condensation
Core Concept:
Aldol reaction occurs between aldehydes/ketones having α–hydrogen in presence of dilute base.
When two different carbonyl compounds react → Cross Aldol Condensation.
Detailed Explanation of Each Option:
Option 1: Cross Aldol Condensation
Acetaldehyde (CH₃CHO) and Propanal (CH₃CH₂CHO):
- Both have α–hydrogen
- Both form enolate ions in base
In aqueous alkali:
Enolate of one aldehyde attacks the carbonyl carbon of the other.
Since two different aldehydes are reacting → Cross Aldol Condensation occurs.
Option 2: Self Aldol Condensation
Self aldol happens when:
Only one aldehyde reacts with itself
Example:
2 CH₃CHO reacting together
But here we have two different aldehydes → not self aldol.
Option 3: Intramolecular Aldol Condensation
Intramolecular aldol occurs:
Within a single molecule containing two carbonyl groups
Example:
Dialdehydes or diketones
But acetaldehyde and propanal are separate molecules → not intramolecular.
Option 4: Cannizzaro Reaction
Cannizzaro occurs only when:
Aldehydes do not have α–hydrogen
Example:
Formaldehyde, Benzaldehyde
But both acetaldehyde and propanal contain α–hydrogen → so they undergo aldol instead.