Karbonyylilisäykset

Karbonyylilisäykset, known in English as carbonyl additions, are a fundamental class of organic reactions where a nucleophile attacks the electrophilic carbonyl carbon of a carbonyl compound, such as an aldehyde or ketone. This attack leads to the formation of a new carbon-nucleophile bond and the breaking of the pi bond within the carbonyl group, resulting in a tetrahedral intermediate.

The carbonyl carbon is electrophilic due to the polar nature of the carbon-oxygen double bond, where oxygen's higher electronegativity draws electron density away from carbon. This polarity makes the carbon susceptible to attack by electron-rich species, or nucleophiles. Common nucleophiles include Grignard reagents, organolithium compounds, cyanide ions, hydride sources like lithium aluminum hydride and sodium borohydride, and water or alcohols in reactions like hydration and acetal formation.

The fate of the tetrahedral intermediate depends on the reaction conditions and the specific nucleophile. In many cases, a subsequent step involves the elimination of a leaving group or protonation to yield the final carbonyl addition product. For example, the addition of Grignard reagents to aldehydes or ketones followed by aqueous workup produces tertiary or secondary alcohols, respectively. Hydride reductions of aldehydes and ketones yield primary and secondary alcohols. Cyanohydrin formation involves the addition of cyanide to form a new carbon-carbon bond and a hydroxyl group. The reversibility of some carbonyl addition reactions, like the hydration of aldehydes, is also a key characteristic.