Answers and Explanations to Problems - Arrow Pushing in Organic Chemistry - page 192

For all the reasons discussed under Problem 1(a), 1(b), and 1(c), the nitrogen anion is
the better nucleophile.
The answer to this question depends on the solvent used for reaction as illustrated in
Figure 3.4. Also relevant is recognition that chloride anions are hard bases and iodide
anion are soft bases. Iodide is the better nucleophile in polar protic solvents while
chloride is the better nucleophile in polar aprotic solvents.
As shown in Appendix 1, the pK a value for hydrocyanic acid is approximately 9.3,
and the pK a value for acetylene is approximately 25. Thus, the acetylene anion is
more reactive than the cyanide anion and is therefore the better nucleophile.
As shown in Appendix 1, the pK a value for methane is approximately 50-75, and the
pK a value for acetonitrile is approximately 25. Thus, the methyl anion is more reac-
tive than the acetonitrile anion and is therefore the better nucleophile.
As shown in Appendix 1, the pK a value for acetone is approximately 20. Furthermore,
the pK a value for acetylacetone is approximately 10 as estimated using the formula