(a) Write resonance structures for the anion of acetonitrile...

Name: Problem 14, Chapter 19: Organic Chemistry
Uploaded: 2020-10-13T08:10:28-08:00
Duration: 4 min 39 s
Channel: Zubair Abdulla
Description: (a) Write resonance structures for the anion of acetonitrile that account for its being much more acidic than ethane. (b) Give a step-by-step mechanism for the condensation of benzaldehyde with acetonitrile.

(a) Write resonance structures for the anion of acetonitrile that account for its being much more acidic than ethane. (b) Give a step-by-step mechanism for the condensation of benzaldehyde with acetonitrile.

Key Concepts

Condensation Reaction Mechanism

A condensation reaction is a process where two molecules combine with the concurrent elimination of a small molecule like water. This mechanism often involves the initial formation of a nucleophilic species that attacks an electrophilic partner, leading to the formation of a key intermediate. Subsequent steps, which include proton transfers and the elimination of a leaving group, complete the transformation. This sequential mechanism is essential in understanding how complex molecules are constructed in synthetic organic chemistry.

Nucleophilic Addition Mechanism

Nucleophilic addition involves a nucleophile—a species rich in electrons—attacking an electrophilic carbon, such as that in a carbonyl group. This step is foundational in carbon–carbon bond forming reactions. The process generally begins with the generation of a nucleophilic species, which subsequently adds to an electron-deficient center, forming a new bond and an intermediate species that can further undergo subsequent transformations.

Conjugate Base Stability and Acidity

The acidity of a compound is determined by the stability of its conjugate base after deprotonation. When deprotonation results in a conjugate base that benefits from resonance stabilization or other electronic effects, the acid is inherently stronger. This relationship is key to comparing the acidities of structurally similar molecules, where the distribution of negative charge significantly impacts the compound’s overall acidity.

Resonance Stabilization

Resonance stabilization refers to the delocalization of electrons in a molecule or ion over separate atoms or bonds. This concept explains how a negative charge formed upon deprotonation can be spread across adjacent atoms, thereby lowering the energy and increasing stability of the conjugate base. It is a fundamental factor that accounts for variations in acidity, as a more stabilized anion corresponds to a stronger acid.

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