7. Substitution Reactions

Would you expect the following conditions to favor S_N1 or S_N2?

(a)

a. Optically active 2-bromobutane undergoes racemization on treatment with a solution of KBr. Give a mechanism for this racemization.

b. In contrast, optically active butan-2-ol does not racemize on treatment with a solution of KOH. Explain why a ­reaction like that in part (a) does not occur.

For each reaction, give the expected substitution product, and predict whether the ­mechanism will be predominantly first order (SN1) or second order (SN2).

d. cyclohexylbromide + methanol

e. cyclohexylbromide + sodium ethoxide

Explain how 1-butanol can be converted into the following compounds:

b.

Suggest a mechanism for the following substitution reactions.

(b)

Fill in the squares in the following chemical equations:

c.

d.

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

(c)

Predict the product of the reaction

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

(d) NH₃

Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product.

To solve this problem, you need to read the description of the Hammett $\sigma$, $\rho$ treatment given in [Chapter 15, Problem 92]. When the rate constants for the hydrolysis of several morpholine enamines of para-substituted propiophenones are determined at pH 4.7, the $\rho$ value is positive; however, when the rates of hydrolysis are determined at pH 10.4, the $\rho$ value is negative.

b. What is the rate-determining step of the hydrolysis reaction when it is carried out in an acidic solution?

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Predict the product(s) that would result when molecules (a)–(p) are allowed to react under the following conditions: (iii) SOCl₂ , NEt₃ (iv) 1. TsCl, Et₃N 2. NaCN; If no reaction occurs, write 'no reaction.'

(o)

Explain why the following alkyl halide does not undergo a substitution reaction, regardless of the base that is used.

For each solvent, indicate the most likely substitution reaction to take place.

(g)

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

(b)