In Chapter 10, you learned how to make an alkyne by acetylide alkylation with a 1° haloalkane. Suggest a mechanism by which this reaction occurs.

Acetylide alkylation, from Assessment 12.61, fails to give the desired product with 2° haloalkanes. Why? What is the actual product of this reaction?

The introduction of elimination reactions provides a second way to synthesize alkynes in a two-step process starting with an alkene. Suggest a mechanism for both steps of this process.

When the reaction scheme in Assessment 12.63 is done on a monosubstituted alkene, at least three equivalents of base are needed. Reacting the product of step 2 with D–Cl (D is an isotope of H) incorporates deuterium at the terminal carbon. Explain these two observations.

Which of the following substitution reactions would you expect to occur more quickly? Explain your answer.

Give a mechanism for the following substitution and elimination reactions.

(a)

Give a mechanism for the following substitution and elimination reactions.

(b)

Give a mechanism for the following substitution and elimination reactions.

(c)

In addition to using mCPBA, epoxides can be synthesized from alkenes in the two-step process shown. Give a mechanism for each step of the process.

The following chlorocyclohexane undergoes neither Sₙ2 nor E2 under the conditions shown. Why?

When trans-4-bromocyclohexanol is treated with base, an intramolecular substitution reaction occurs to give a cyclic ether. This product does not form when cis-4-bromocyclohexanol is reacted under the same conditions. Explain these observations.

The following substitution reaction, between a strong base and a 1° haloalkane, occurs in a single step via backside displacement. Yet it is not technically an S_N2 reaction. Why?

Which is a better leaving group, HO⁻ or H₂O? Explain your answer.

Using pKₐ values, calculate K_eq for the following acid–base reaction.

Suggest a mechanism for the following reactions.

(a) Substitution:

Suggest a mechanism for the following reactions.

(b) Substitution :

Suggest a mechanism for the following reactions.

(c) Elimination:

In this, and previous, chapters, we have seen 1,2-alkyl and 1,2-hydride shifts. If both are possible, as in the carbocation shown, which would you expect to occur? Explain your answer.

The bromoalkanes shown below participate in S_N1 reactions with the relative rates shown. Explain this trend. relative rate:

Of the three possible elimination mechanisms (Figure 12.50), this chapter focused on two of them (E1 and E2). The third possibility occurs in situations like the one below. What makes this mechanism favored under these conditions?

In Chapter 8, we learned about the chemistry of terpenes and the interesting reactions they can undergo. One such reaction is the acid-catalyzed conversion of nerol to terpineol. Suggest a mechanism for this transformation

.

Crown ethers are able to solvate cations based on their size. Specifically, 15-crown-5 forms stable complexes with sodium. How would the addition of a crown ether change the rate of an S_N2 reaction?