7. Substitution Reactions

For each pair, choose the nucleophile that would react most quickly in an S_N2 reaction (assume H₂O is the solvent).

(d)

When (±)−2,3−dibromobutane reacts with potassium hydroxide, some of the products are (2S,3R)-3-bromobutan-2-ol and its enantiomer and trans-2-bromobut-2-ene. Why is no cis-2-bromobut-2-ene formed?

Predict the compound in each pair that will undergo the S_N2 reaction faster.

(c)

(d)

Which of the following S_N2 reactions should proceed at a faster rate? Justify your answer on a reaction coordinate diagram.

Explain why the alkyl halide shown here reacts much more rapidly with guanine than does a primary alkyl halide (such as pentyl chloride).

Give two syntheses for (CH₃)₂CH—O—CH₂CH₃, and explain which synthesis is better.

For each pair, choose the haloalkane that would react most quickly in an S_N2 reaction.

(b)

How will the rate of each of the following S_N2 reactions change if it is carried out in a more polar solvent?

c.

Explain why a much better yield of primary amine is obtained from the reaction of an alkyl halide with azide ion (^-N₃), followed by catalytic hydrogenation. (Hint: An alkyl azide is not nucleophilic.)

Amines are good nucleophiles, even though they are neutral. How would the rate of an S_N2 reaction between an amine and an alkyl halide be affected if the polarity of the solvent is increased?

Draw the products obtained from the S_N2 reaction of:

c. (S)-3-chlorohexane and hydroxide ion.

d. 3-iodopentane and hydroxide ion.

For each pair, choose the nucleophile that would react most quickly in an S_N2 reaction (assume H₂O is the solvent).

(a) F^- vs Br^-

The following reaction, though run under standard solvolysis conditions, occurs via an S_N2 reaction. Why?

Predict the product of the following reaction.

The rate of the reaction of methyl iodide with quinuclidine was measured in nitrobenzene, and then the rate of the reaction of methyl iodide with ­triethylamine was measured in the same solvent. The concentration of the reagents was the same in both experiments.

a.Which reaction had the larger rate constant?