7. Substitution Reactions

Which reaction in each of the following pairs takes place more rapidly? (EtOH is ethyl alcohol; Et₂O is diethyl ether.)

d.

e.

Under which of the following reaction conditions will (R)-1-chloro-1-phenylethane form the most (R)-1-phenyl-1-ethanol: in water or in 1.0 M HO⁻?

Draw the substitution products for each of the following reactions; if the products can exist as stereoisomers, show what stereoisomers are obtained:

e. 1-bromo-2-butene + CH₃O⁻

f. 1-bromo-2-butene + CH₃OH

Suggest a reagent to carry out each of the following conversions to an alcohol.

(a)

When (R)-(1-bromoethyl)benzene is treated with sodium cyanide, a single enantiomer is produced. However, upon treatment of the same molecule with water, a mixture of two enantiomers is obtained.

(a) Explain these results.

(b) Why is only partial racemization sometimes observed?

Order the following molecules on the basis of their nucleophilic strength using the pKₐ values of their conjugate acids.

Suggest a reagent to carry out each of the following conversions to an alcohol.

(c)

Predict the product(s) of the following reactions.

(f)

Predict the product(s) of the following reactions.

(g)

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.

Which of the following reactions take place more rapidly when the concentration of the nucleophile is increased?

Starting with (R)-1-deuterio-1-propanol, how could you prepare

c. (R)-1-deuterio-1-methoxypropane?

Even with an excess of cyanide, only one equivalent will react with the following dibromoalkane. To which carbon will the cyanide add? Predict the product and explain your choice.

Suggest a mechanism for the following reactions.

(a) Substitution:

Predict the product(s) that would result when molecules (a)–(p) are allowed to react under the following conditions: (i) SOCl₂ ; (ii) PBr₃ ; (iii) SOCl₂ , NEt₃ (iv) 1. TsCl, Et₃N 2. NaCN; (v) 1. TsCl, Et₃N 2. NaOt-Bu (vi) H₂SO₄ (vii) HCl; (viii) HBr; (ix) PCC; (x) H₂CrO₄ , H₂O (xi) HOCl, H₂O (xii) HIO₄ If no reaction occurs, write 'no reaction.'

(o)