Alkoxide Ion

Definition

An alkoxide ion is a negatively charged species formed when an alkyl group (R-) is bonded to an oxygen atom. It is a key intermediate in various organic chemistry reactions, including the preparation of ethers, nucleophilic addition reactions of aldehydes and ketones, and the hydration of carboxylic acids.

5 Must Know Facts For Your Next Test

1. Alkoxide ions are formed when an alkyl group replaces the hydrogen atom of an alcohol, creating a negatively charged oxygen species.
2. In the preparation of ethers, alkoxide ions act as nucleophiles, attacking an alkyl halide to form the ether product.
3. Alkoxide ions are important nucleophiles in the nucleophilic addition reactions of aldehydes and ketones, where they add to the carbonyl carbon.
4. During the hydration of carboxylic acids, the alkoxide ion intermediate is a key step in the formation of the tetrahedral, carbocation-like transition state.
5. The reactivity and stability of alkoxide ions can be influenced by the nature of the alkyl group, with larger, more substituted alkyl groups generally leading to more stable alkoxide ions.

Review Questions

• Explain the role of alkoxide ions in the preparation of ethers.
  • Alkoxide ions are key intermediates in the preparation of ethers. They act as nucleophiles, attacking an alkyl halide in an $\text{S}_\text{N}2$ reaction. The alkoxide ion displaces the halide, forming the ether product. This reaction is a common method for synthesizing symmetrical and unsymmetrical ethers, with the alkoxide ion serving as a crucial reactive species.
• Describe how alkoxide ions participate in the nucleophilic addition reactions of aldehydes and ketones.
  • In the nucleophilic addition reactions of aldehydes and ketones, alkoxide ions act as powerful nucleophiles. They add to the electrophilic carbonyl carbon, forming a tetrahedral intermediate. This intermediate then collapses, expelling the alkoxide ion and generating the addition product. The ability of alkoxide ions to serve as effective nucleophiles is crucial for these types of reactions, which are important in the synthesis of alcohols and other oxygenated organic compounds.
• Analyze the role of alkoxide ions in the hydration of carboxylic acids.
  • The hydration of carboxylic acids involves the formation of an alkoxide ion intermediate. During this process, water acts as a nucleophile, attacking the carbonyl carbon of the carboxylic acid. This generates a tetrahedral, carbocation-like transition state, with the alkoxide ion as a key intermediate. The alkoxide ion then facilitates the collapse of this transition state, leading to the formation of the hydrated carboxylic acid product. The stability and reactivity of the alkoxide ion significantly influence the kinetics and thermodynamics of this important hydration reaction.

Related terms

Alkyl Group: A hydrocarbon chain, such as methyl (CH3-), ethyl (CH3CH2-), or propyl (CH3CH2CH2-), that is attached to another atom or functional group.

Nucleophile: A species that donates a pair of electrons to form a new covalent bond, often in reactions involving the addition of a nucleophile to an electrophilic carbon.

Hydration: The addition of water (H2O) to a molecule, resulting in the incorporation of the hydrogen and hydroxyl groups.