7. Substitution Reactions

Propose an S_N1 mechanism for the solvolysis of 3-bromo-2,3-dimethylpentane in ethanol.

Predict the compound in each pair that will undergo solvolysis (in aqueous ethanol) more rapidly.

(a) (CH₃CH₂)₂CH—Cl or (CH₃)₃C—Cl

(b)

Choose the member of each pair that will react faster by the S_N1 mechanism.

a. 1-bromopropane or 2-bromopropane

b. 2-bromo-2-methylbutane or 2-bromo-3-methylbutane

Furfuryl chloride can undergo substitution by both S_N2 and S_N1 mechanisms. Because it is a 1° alkyl halide, we expect S_N2 but not S_N1 reactions. Draw a mechanism for the S_N1 reaction shown below, paying careful attention to the structure of the intermediate. How can this primary halide undergo S_N1 reactions?

Optically active butan-2-ol racemizes in dilute acid. Propose a mechanism for this racemization.

Draw the stereoisomers that are formed from the following S_N1 reactions:

a. 3-bromo-3-methylpentane and methanol

b. 3-chloro-3-methylhexane and methanol

Rank the following from most reactive to least reactive in an S_N1 reaction:

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

Practice your electron-pushing skills by drawing a mechanism for the following S_N1 reactions.

(c)

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

(a)

Which of the following S_N1 reactions should proceed at a faster rate? Justify your answer on a reaction coordinate diagram.

Practice your electron-pushing skills by drawing a mechanism for the following S_N1 reactions.

(a)

The allylic bromide below gives two S_N1 products. Justify the formation of each.

Rank the ability of the following compounds to undergo an S_N1 reaction ( 1 = fastest, 5 = slowest ).

Propose a mechanism for each reaction, showing explicitly how the observed mixtures of products are formed.

(b) 2-methylbut-3-en-2-ol + HBr → 1-bromo-3-methylbut-2-ene + 3-bromo-3-methylbut-1-ene