8.7: Problems for Chapter 8

Última actualización
Guardar como PDF

Page ID: 2375

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)

Link to Solution Manual

P8.1: Rank the following molecules in order of how fast they would be expected to react with CH₃SNa in acetone:

P8.2: Draw line structures representing the most stable carbocation with the given molecular formula:

a) C₃H₇⁺

b) C₄H₉⁺

c) C₃H₈N⁺

d) C₄H₇⁺

P8.3: Which of the two carbocations below is expected to be lower in energy? Explain your reasoning.

P8.4: Arrange the following species in order of increasing nucleophilicity.

P8.5: Predict the organic products of the following S_N2 reactions. Indicate stereochemistry.

P8.6: Which of the S_N2 reactions in the previous problem is likely to have a first order rate expression? Explain.

P8.7: From the following pairs, select the better nucleophile:

a) water or hydroxide ion

b) CH₃S^- or CH₃OH

c) CH₂S^- or CH₃SH

d) acetate ion or hydroxide ion

e) diethyl sulfide or diethyl ether

f) dimethylamine or diethylether

g) trimethylamine or 2,2-dimethylpropane

P8.8: Methyl iodide (0.10 mole) is added to a solution that contains 0.10 mole NaOCH₃ and 0.10 mole NaSCH₃ in ethanol solvent. Predict the major product that would be isolated, and explain your reasoning.

P8.9: For each pair of compounds, predict which will more rapidly undergo S_N1 solvolysis in a water/methanol solvent.

P8.10: Predict the solvolysis products (considering stereochemistry) of each of the reactions below. Show the carbocation intermediate in each reaction.

P8.11: The following compounds are all direct products of nucleophilic substitution reactions. Show the starting compounds.

P8.12: The following is the final step in the formation of a ‘disulfide bond’ between two cysteine residues within a protein (we’ll learn more about disulfide bonds in section 16.12A). Propose a mechanism for this process, using H-A and :B to represent catalytic acid and base groups. Label those atoms which are acting as nucleophile, electrophile, and leaving group, respectively.

P8.13: The figure below shows the regeneration of the disulfide bond in a coenzyme called lipoamide (we’ll learn more about one very important metabolic role of lipoamide in section 16.12B). In the process, a disulfide bond in the enzyme is broken to release two free cysteines. Propose a likely mechanism for this transformation (hint – there are two S_N2 displacements involved).

P8.14: The ‘bicyclo’ compound shown below is very unreactive in S_N1 reactions, even though it is a tertiary alkyl halide. Explain. (Hint – consider bond geometry - a model will be very helpful!)

Challenge problems

C8.1:In a classic experiment in physical organic chemistry, (R)-2-iodooctane was allowed to react with a radioactive isotope of iodide ion, and the researchers monitored how fast the radioactive iodide was incorporated into the alkane (the rate of incorporation, k_i ) and also how fast optical activity was lost (the rate of racemization, k_r). They found that the rate of racemization was, within experimental error, equal to twice the rate of incorporation. Discuss the significance of this result - what does it say about the actual mechanism of the reaction?

Template:Soderberg