Karbonyylilisäys

Karbonyylilisäys, also known as carbonyl addition, is a fundamental organic reaction where a nucleophile adds to the carbonyl group of an aldehyde or ketone. The carbonyl group, characterized by a carbon-oxygen double bond, is highly polarized due to the electronegativity of oxygen, making the carbon atom electrophilic and susceptible to attack by electron-rich species. This reaction is a cornerstone of organic synthesis, enabling the formation of new carbon-carbon or carbon-heteroatom bonds.

The general mechanism involves the nucleophile attacking the electrophilic carbonyl carbon, breaking the pi bond and forming a tetrahedral intermediate. This intermediate typically carries a negative charge on the oxygen atom. In many cases, this intermediate is then protonated by an acidic source, leading to the formation of an alcohol or a related functional group. Common nucleophiles that participate in carbonyl addition reactions include Grignard reagents, organolithium compounds, cyanide ions, and hydride reagents.

The reactivity of aldehydes and ketones towards nucleophilic addition is influenced by several factors. Steric hindrance around the carbonyl group can impede the approach of the nucleophile, slowing down the reaction. Electron-donating groups attached to the carbonyl carbon decrease its electrophilicity, making it less reactive, while electron-withdrawing groups enhance it. The reaction conditions, such as solvent and temperature, also play a significant role in the reaction rate and outcome. Carbonyl addition reactions are widely used in the synthesis of alcohols, carboxylic acids, and various other valuable organic compounds.