The presence of a negative charge and an unshared electron pair on carbon makes acetylide anions strongly nucleophilic. As result, they react with many different kinds of electophiles.
Problem8.9 the pk of acetone CHCOCH, is 19.3 which of the following bases is strong enough to deprotonate acetone?
8.8 Alkylation of Acetylide Anions
The negative charge and unshared electron pair on carbon make an acetylide anion strongly nucleophilic. As a result, an acetylide anion can react with an alkyl halide such as bromomethane to substitute forhalogen and yield a new alkyne product.
We won’t study the details of this substitution reaction until Chapter 11 but for now can picture it as happening by the pathway shown in Figure 8.6 The nucleophilic acetylide ion uses an electron pair to from a bond to the positively polarized, electophilic carbon atom of bromomethane. As the new C-C bond forms, Br-departs , taking with it electron pair form the former C-Br bond and yielding propyne as product. We call such a reaction an alkylation because a new alkyl group has become attached to the starting alkyne.