Chemistry Reference
In-Depth Information
Scheme 7.11 Addition of nucleophiles to carbonyls is reversible.
produces alcohols from carbonyls. Because of the trigonal planar geometry of a carbonyl
group, there is no stereochemical preference associated with these addition reactions.
When considering reactions involving the addition of nucleophiles to carbonyls, it is
important to understand that many nucleophiles can also serve as leaving groups.
Therefore, to prevent the reverse reaction (elimination of the added nucleophile) illustrated
in Scheme 7.11, carbon-based nucleophiles are generally utilized. Such nucleophiles
include, but are not limited to, Grignard reagents, alkyllithium reagents, and potassium
cyanide. In the case of Grignard and alkyllithium reagents, the result is formation of
alcohols. Using potassium cyanide, cyanohydrins are formed. These reagents and the
products of their reactions with acetone are illustrated in Scheme 7.12.
Thus far, all examples related to the addition of nucleophiles to carbonyls involve basic
(anionic) conditions. However, such conditions are not required. Recalling that a carbonyl
oxygen atom possesses a partial negative charge, we recognize that under acidic conditions
it can be protonated. The protonation of carbonyl groups, illustrated in Scheme 7.13, was
discussed in Chapter 3. Thus, as shown in Scheme 7.14 using acetone, treatment of
Scheme 7.12 Products resulting from addition of nucleophiles to acetone.
