7. Substitution Reactions

Draw the substitution product formed by each of the following S_N2 reactions:

a. trans-1-iodo-4-ethylcyclohexane and methoxide ion

b. cis-1-chloro-3-methylcyclobutane and ethoxide ion

Draw a perspective structure or a Fischer projection for the products of the following S_N2 reactions.

(f)

Which substitution reaction takes place more rapidly?

c.

Predict the major products of the following substitutions.

d. CH₃CH₂CH₂I + NaCN →

Which substitution reaction takes place more rapidly?

b.

Under certain conditions, the reaction of 0.5 M 1-bromobutane with 1.0 M sodium methoxide forms 1-methoxybutane at a rate of 0.05 mol/L per second.

c. Show another S_N2 reaction using a different combination of an alkoxide and an alkyl bromide that also produces 1-methoxybutane.

Consider the reaction of 1-bromobutane with a large excess of ammonia (NH₃). Draw the reactants, the transition state, and the products. Note that the initial product is the salt of an amine (RNH₃⁺Br⁻), which is deprotonated by the excess ammonia to give the amine.

Write the mechanism for the reaction of a cysteine side chain with iodoacetic acid.

Under appropriate conditions, (S)-1-bromo-1-fluoroethane reacts with sodium methoxide to give pure (S)-1-fluoro-1-methoxyethane.

a. Why is bromide rather than fluoride replaced?

b. Draw perspective structures (as shown on the previous page for 2-bromobutane) for the starting material, the transition state, and the product.

c. Does the product show retention or inversion of configuration? d. Is this result consistent with reaction by the SN2 mechanism?

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

(a)

Show all the products, including their configurations, that are obtained from the above reaction.

Rank the following alkyl bromides from most reactive to least reactive in an S_N2 reaction:

1-bromo-2-methylbutane, 1-bromo-3-methylbutane, 2-bromo-2-methylbutane, and 1-bromopentane.

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

(c)

Draw a perspective structure or a Fischer projection for the products of the following S_N2 reactions.

(c)

(d)