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🥼organic chemistry review

Alkoxide Ions

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

Alkoxide ions are negatively charged species formed when an alkoxide group (R-O-) is detached from a neutral alkoxide compound. These ions are important intermediates in many organic reactions, particularly in the context of understanding formal charges.

5 Must Know Facts For Your Next Test

  1. Alkoxide ions are strong nucleophiles due to the presence of a lone pair of electrons on the oxygen atom.
  2. The formal charge on an alkoxide ion is -1, as the oxygen atom has gained an extra electron compared to a neutral alkoxide group.
  3. Alkoxide ions can be generated through the reaction of alcohols with a strong base, such as sodium hydride or n-butyllithium.
  4. Alkoxide ions are commonly used as nucleophiles in organic reactions, such as nucleophilic substitutions and additions.
  5. The basicity and nucleophilicity of alkoxide ions can be tuned by the choice of the alkyl group (R-) attached to the oxygen atom.

Review Questions

  • Explain how the formal charge on an alkoxide ion is determined and why it is important in understanding reactivity.
    • The formal charge on an alkoxide ion is -1, as the oxygen atom has gained an extra electron compared to a neutral alkoxide group. This formal charge is important because it directly influences the reactivity of the alkoxide ion. The negative charge on the oxygen atom makes it a strong nucleophile, allowing it to readily donate its lone pair of electrons to electrophilic carbon atoms in various organic reactions. Understanding the formal charge on alkoxide ions is crucial for predicting their behavior and reactivity in these processes.
  • Describe the relationship between alkoxide ions and their use as nucleophiles in organic reactions.
    • Alkoxide ions are highly reactive due to the presence of a lone pair of electrons on the oxygen atom, which gives them strong nucleophilic character. This nucleophilicity allows alkoxide ions to participate in a variety of organic reactions, such as nucleophilic substitutions and additions, where they can attack electrophilic carbon centers. The ability to generate alkoxide ions from alcohols and strong bases, and the tunability of their reactivity based on the alkyl group, make them versatile and important intermediates in many organic transformations.
  • Evaluate the factors that influence the basicity and nucleophilicity of alkoxide ions, and how these properties impact their reactivity in organic chemistry.
    • The basicity and nucleophilicity of alkoxide ions are influenced by the nature of the alkyl group (R-) attached to the oxygen atom. Larger, more polarizable alkyl groups tend to stabilize the negative charge on the oxygen, resulting in more basic and nucleophilic alkoxide ions. Conversely, smaller or more electronegative alkyl groups can decrease the basicity and nucleophilicity of the alkoxide ion. These properties directly impact the reactivity of alkoxide ions in organic reactions, as more basic and nucleophilic species will be more likely to participate in processes like nucleophilic substitutions and additions. Understanding these factors is crucial for predicting and controlling the behavior of alkoxide ions in synthetic organic chemistry.