key term - Deprotonation

Definition

Deprotonation is the process of removing a proton (H+) from a molecule or ion, resulting in the formation of a negatively charged species. This chemical reaction is central to various organic chemistry topics, as it allows for the generation of reactive intermediates and the manipulation of molecular structures.

5 Must Know Facts For Your Next Test

1. Deprotonation is a crucial step in the formation of acetylide anions, which are important intermediates in alkyne chemistry (Topic 9.7).
2. The deprotonation of alcohols is a key step in the nucleophilic addition reaction to form acetals (Topic 19.10).
3. Deprotonation of enols allows for α-substitution reactions, where a new substituent is introduced at the α-carbon (Topic 22.2).
4. The Claisen condensation reaction involves the deprotonation of a carbonyl compound to generate an enolate intermediate (Topic 23.7).
5. The ionization state of amino acids is determined by the deprotonation and protonation of the carboxyl and amino groups (Topics 26.1 and 26.2).

Review Questions

• Explain the role of deprotonation in the formation of acetylide anions and how this relates to the reactivity of alkynes.
  • Deprotonation is a key step in the formation of acetylide anions, which are important reactive intermediates in alkyne chemistry (Topic 9.7). When a terminal alkyne is treated with a strong base, such as n-butyllithium or sodium amide, the acidic hydrogen on the alkyne is removed, generating a negatively charged acetylide anion. This highly reactive species can then undergo various nucleophilic addition and substitution reactions, allowing for the synthesis of diverse alkyne-containing compounds.
• Describe how deprotonation is involved in the nucleophilic addition of alcohols to form acetals, and discuss the importance of this reaction in organic synthesis.
  • The deprotonation of alcohols is a crucial step in the nucleophilic addition reaction to form acetals (Topic 19.10). When an alcohol is treated with an acid catalyst, the alcohol is first deprotonated, generating an alkoxide ion. This highly reactive nucleophile can then attack the carbonyl carbon of an aldehyde or ketone, leading to the formation of a tetrahedral intermediate. Further deprotonation and elimination steps result in the production of an acetal, a valuable functional group that is widely used in organic synthesis as a protecting group for carbonyl compounds.
• Analyze the role of deprotonation in the reactivity of enols and how this relates to the α-substitution reactions discussed in Topic 22.2.
  • The deprotonation of enols is a key step in the α-substitution reactions discussed in Topic 22.2. Enols are neutral, weakly acidic compounds that can be deprotonated by a base to form enolate ions, which are highly reactive nucleophilic species. These enolate intermediates can then undergo a variety of substitution reactions at the α-carbon, allowing for the introduction of new substituents. The ability to selectively deprotonate enols and generate enolate anions is a powerful tool in organic synthesis, enabling the construction of more complex molecular structures through strategic α-functionalization.

Related terms

Proton:

A positively charged subatomic particle that is a fundamental component of the nucleus of an atom.

Base:

A chemical species that can accept a proton, forming a conjugate acid-base pair.

Conjugate Base:

The species formed when a base accepts a proton, resulting in the loss of a proton from the original molecule.