Alkoxides

Definition

Alkoxides are negatively charged species formed when an alkoxide group, consisting of an alkyl group bonded to an oxygen atom, replaces a hydrogen atom on a molecule. They are important intermediates in various organic reactions, particularly in the context of the SN2 reaction and the E1 and E1cB elimination reactions.

5 Must Know Facts For Your Next Test

1. Alkoxides are strong nucleophiles and are commonly used as bases in organic reactions.
2. In the SN2 reaction, alkoxides can act as nucleophiles to displace a leaving group, leading to the formation of new carbon-oxygen bonds.
3. Alkoxides can also participate in E1 and E1cB elimination reactions, where they abstract a proton from a substrate, resulting in the formation of a new carbon-carbon double bond.
4. The reactivity of alkoxides is influenced by factors such as the nature of the alkyl group, the solvent, and the presence of other substituents on the molecule.
5. Alkoxides can be generated through the reaction of alcohols with strong bases, such as sodium hydride or alkyllithium reagents.

Review Questions

• Explain how alkoxides can participate in the SN2 reaction and describe the key features of this mechanism.
  • In the SN2 reaction, alkoxides can act as nucleophiles, attacking the carbon atom bearing the leaving group in a backside manner. This results in the inversion of stereochemistry at the carbon center and the formation of a new carbon-oxygen bond. The nucleophilicity of the alkoxide, the nature of the leaving group, and the steric hindrance around the carbon center are all important factors that influence the rate and outcome of the SN2 reaction.
• Discuss the role of alkoxides in E1 and E1cB elimination reactions, and compare the key differences between these two mechanisms.
  • Alkoxides can participate in both E1 and E1cB elimination reactions. In the E1 mechanism, the alkoxide abstracts a proton from the substrate, forming a carbocation intermediate, which then undergoes elimination to generate a new carbon-carbon double bond. In the E1cB mechanism, the alkoxide acts as a base, directly removing a proton from the substrate, leading to the formation of the double bond without the formation of a carbocation intermediate. The E1cB mechanism is typically favored over the E1 mechanism when the substrate has a good leaving group and the resulting carbocation would be unstable.
• Analyze the factors that influence the reactivity and selectivity of alkoxides in organic reactions, and explain how these factors can be leveraged to control the outcome of the reaction.
  • The reactivity and selectivity of alkoxides in organic reactions are influenced by various factors, such as the nature of the alkyl group, the solvent, the presence of other substituents, and the reaction conditions. For example, the size and electronegativity of the alkyl group can affect the nucleophilicity and basicity of the alkoxide, influencing its ability to participate in substitution or elimination reactions. The choice of solvent can also impact the solubility and reactivity of the alkoxide, as well as the stability of any intermediates formed. Additionally, the presence of other functional groups or substituents on the substrate can lead to selective reactivity or the formation of specific products. By carefully considering and manipulating these factors, organic chemists can control the outcome of reactions involving alkoxides and achieve the desired products.

Related terms

Alkyl Group: An alkyl group is a hydrocarbon substituent derived from an alkane by the removal of a single hydrogen atom.

Nucleophile: A nucleophile is a species that donates an electron pair to form a new covalent bond in a chemical reaction.

Leaving Group: A leaving group is an atom or group that departs with a pair of electrons during a substitution or elimination reaction.