I'm trying to understand the nucleophilicity of alkynes, my book lists the pKa's of acetylene (HCCH), ethylene (CH2CH2), and methane (CH3CH3) as 25, 44, and 50 respectively. This leads to the conclusion that HCCH -acetylene- is the strongest acid and hence the weakest base. The book then goes on to say that acetylide anions are highly basic (compared to ethyl anion and methyl anion assumably) and is thus the strongest nucleophile. This seems to me to be a contradiction, the book clearly states that methyl anion is more basic than vinyl anion which is in turn more basic than acetylide anion. Then proceeds to say that actylide ion is highly nucleophilic. How does this work?