CHM 233 : Fall 2018 Quiz #12 - Answer Key Question 1 MCalkenesIn Which are the best reagents/conditions for the following reaction?

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1 M 233 : Fall 2018 Quiz #12 - nswer Key Question 1 MalkenesIn Which are the best reagents/conditions for the following reaction? 2 / 2 S 4 (cat.) conc. 2 S 4 /heat 1. 3.TF 2. Na/ g(c) 2 / 2 2. Na 4 2 / 2 S 4 (cat.) Markovnikov-like addition of 2 across the = bond WIT rearrangement, requires a carbocation intermediate and this a RNSTE acid catalyst

2 Question 2 M26n Which is MST LIKELY to be the major product of the following reaction???? 3 Me Me Me Me L/ /L = Me Me L/ /L Me L Me L

3 Question 3 MalkenesIh Which is the expected major organic product of the following reaction 2??? Et (solvent) Et 2 is a Lewis acid that is strong enough to react with a = bond, Et is not, thus: the Et MUST add from the Et "top" Et Et Et assume the 2 adds to the "bottom of the = bond (if it added to the top a stereoisomer would result that is not important in the present context) Et adds to the bromonium and not because there are many more Et molecules than

4 Question 4 MalkenesIp Which are the best reagents/conditions to perform the following reaction (±) 2 / 2 S 4 (cat.) conc. 2 S 4 /heat 1. 3.TF 2. Na/ g(c) 2 / 2 2. Na TF 2. Na/ 2 2 (±) NTI-Markovnikov addition of 2 across the = bond WITUT rearrangement Requires hydroboration

5 Question 5 M26s Which are the reagents and conditions that are most likely to give the products of the following reactions? 1) 1. g(c) 2 / 2 2. Na 4 2) 3) 2 2 S 4 (cat.)/heat TF / Reaction 1) 2 / 2 S 4 (cat.)/heat Reaction 2) 1. g(c) 2 / 2, 2. Na 4 Reaction 3) TF, / Reaction 1) TF, / Reaction 2) 1. g(c) 2 / 2, 2. Na 4 Reaction 3) 2 / 2 S 4 (cat.)/heat Reaction 1) 1. g(c) 2 / 2, 2. Na 4 Reaction 2) 2 / 2 S 4 (cat.)/heat Reaction 3) TF, / Reaction 1) TF, / Reaction 2) 2 / 2 S 4 (cat.)/heat Reaction 3) 1. g(c) 2 / 2, 2. Na 4 2 / 2 S 4 (cat.)/heat results in Markovnikov-type addition of 2, but involves a carbocation intermediate that will rearrange if possible, as in these reactions 1. g(c) 2 / 2, 2. Na 4 results in Markovnikov addition of 2 across the = bond, but avoids a carbocation intermediate, rearrangements do not occur, this is the preferred method for Markovnikov water addition, do NT use aqueous acid in a synthesis problem TF, / results in NTI-Markovnikov addition of 2 across the = bond, avoids a carbocation intermediate, rearrangements do not occur

6 Question 6 MalkenesIu Give the best reagents/conditions to perform the following reaction??? 2 / 2 S 4 (cat.) conc. 2 S 4 /heat 1. 3.TF 2. Na/ g(c) 2 / 2 2. Na 4 1. g(c) 2 / 2 2. Na 4 Markovnikov addition WITUT RERRNGEMENT must be oxymercuration

7 Question 7 M20q Using the homolytic bond dissociation energies provided, which statement best describes the following reaction? + +..E. (kcal/mol) The reaction is exothermic by 41 kcal/mol The reaction is exothermic by 5 kcal/mol The reaction is endothermic by 5 kcal/mol The reaction is endothermic by 41 kcal/mol Even though the reaction involves heterolytic bond cleavage in Lewis acid/base reactions, we are only comparing the reactants and products The bond dissocaition energies measure the energies of the electrons in bonds, and reactions involve breaking bonds and making new ones ll we need to do is to compare the energy cost of breaking the bonds that are broken to the energy gain of the bonds that are made Energy "cost" due to breaking bonds = 86 (-) + 88 (-) Total = 174 kcal/mol Energy "gain" due to making bonds = 68 (-) (-) Total = 179 kcal/mol Electron energy in products lower than in reactants (the bonds are stronger in the products than in the reactants, thus the reaction is EXTERMI by = 5 kcal/mol

8 Question 8 MalkenesIs nly one of the following reactions actually gives the provide product, the other reactions actually give different products. Identify the correct reaction. (ignore stereochemistry in this problem) 4-ethyl-3-heptene 1. 3.TF 2. Na/ ethyl-2-heptene 1. 2 /g(c) 2 2. Na 4 3-ethyl-3-heptene 1. 3.TF 2. Na/ ethyl-3-heptene 1. 2 /g(c) 2 2. Na 4 4-ethyl-3-heptene 1. 3.TF 2. Na/ ethyl-2-heptene 1. 2 /g(c) 2 2. Na 4 3-ethyl-3-heptene 1. 2 /g(c) 2 2. Na 4