7. Substitution Reactions

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.

Predict the product of the following substitution reactions, paying close attention to the stereochemical outcome of the reactions.

(b)

The benzylic bromide shown undergoes neither S_N1 nor S_N2 substitution reactions. Explain.

Propose a mechanism for the following reaction.

Explain the difference in reactivity between CH₃O⁺H₂ and CH₃OH in a nucleophilic substitution reaction. (The pK_a of H₃O⁺ is −1.7.)

Give a mechanism for the following substitution and elimination reactions.

(c)

Would the following nucleophiles be more likely to participate in an S_N1 or S_N2 reaction?

(c)

Predict the product(s) that would result when molecules (a)–(p) are allowed to react under the following conditions:(vii) HCl; (viii) HBr If no reaction occurs, write 'no reaction.'

(k)

Predict the product(s) of the following reactions.

(g)

Predict the product for the following substitution reactions. Indicate whether each reaction likely proceeds by an S_N1 or S_N2 mechanism.

(c)

Provide a mechanism for the following S_N1 reactions that feature a rearrangement.

(b)

Would you expect the following substitution reaction to proceed with inversion or racemization? Why?

What is the major product of each of the following reactions?

c.

Draw the substitution products for each of the following S_N2 reactions. If the ­products can exist as stereoisomers, show which stereoisomers are formed:

a. (3S,4S)-3-bromo-4-methylhexane + CH₃O^-

b. (3S,4R)-3-bromo-4-methylhexane + CH₃O^-

Chlorocyclohexane reacts with sodium cyanide (NaCN) in ethanol to give cyanocyclohexane. The rate of formation of cyanocyclohexane increases when a small amount of sodium iodide is added to the solution. Explain this acceleration in the rate.