Organic Chemistry 2301, Section 003

Fall 2023

EXAM 3

1) (40 points) Give the expected major organic product of each of the following reactions. You do not need to indicate stereochemistry.

2) (30 points) When (S)-2-bromobutane is treated with sodium methoxide in methanol, the major product is trans-2-butene.

(a) What is the most likely mechanism for this reaction? Give the type (SN1, SN2, E1 or E2), not the actual mechanism (no steps or arrows etc).

(b) Sketch a picture of the transition state (TS) for the rate determining step in this reaction. Make it clear what bonds remain largely unaffected in the TS and which bonds are partially formed or broken in the TS. Make sure stereochemistry is clear in your picture.

(c) What happens to the reaction rate if the concentration of the alkyl bromide is doubled? Does it increase, decrease or stay approximately the same? If it changes, indicate by how much (give a number).

(d) What happens to the reaction rate if the concentration of the sodium methoxide is doubled? Does it increase, decrease or stay approximately the same? If it changes, indicate by how much (give a number).

(e) Now provide a mechanism for the above reaction. Your mechanism should include the structures of the reactants and any intermediates along with curved arrows showing the movement of electrons. Show all lone pairs and charges in your structures.

3) (25 points) Provide a mechanism for the following reaction. Your mechanism should include the structures of the reactants and any intermediates along with curved arrows showing the movement of electrons. Show all lone pairs and charges in your structures.

4) (20 points) Place the following in increasing order of rate of SN2 reaction. Assume the solvent and nucleophile are the same for all. (1= slowest SN2 rate, 4 = fastest SN2 rate)

5) (15 points) Treatment of Compound 1 shown below with a strong base leads to the formation of one Major Elimination Product. Provide a structure for that Major Elimination Product using the template shown. Note: the tert-butyl group in the product should appear on the carbon indicated with a (•).

6) (30 points) Consider the reaction sequence shown below:

(a) Treatment of the Starting Material shown with tosyl chloride in pyridine leads to the formation of Compound 1. Use the Fisher projection template provided below to indicate the stereochemistry in the product, Compound 1.

(b) Use the template provided below to indicate the stereochemistry in the product, Compound 1.

(c) Subsequent treatment of Compound 1 with sodium methanethiolate in water leads to the formation of Compound 2. Use the Fisher projection template provided below to indicate the stereochemistry in the product, Compound 2.

7) (20 points) Mark an X for which species in each matches the description. Only mark one answer per set. For nucleophile comparisons, assume the solvent is CH3OH. Unclear or illegible answers will receive no credit.

a. fastest reaction with HCl

b. more stable (lower energy) alkene

c. stronger nucleophile

d. polar protic solvent

e. stronger nucleophile

8) (20 points) A solution of acetic acid in isopropanol contained an impurity that was purified and characterized. Exact mass spectrometry gave a mass of 102.07 indicating a molecular formula of C5H10O2. The 1 H NMR and IR spectrum for the impurity are shown below.

(a) Propose a structure for the impurity.

(b) Redraw your proposed structure and indicate which protons correspond to which peaks in the 1 H NMR. For example, draw an arrow to a proton in your structure and label it with “Doublet, 6 H”.

(c) What feature in the IR spectrum is useful for confirming the structure of the proposed product?