Deck 6: Chemical Reactivity and Mechanisms

Question 1

Predict the sign of $\Delta$ S of the following reaction.

A) positive
B) negative
C) no change

Answer 1

positive

Question 2

Predict the sign of $\Delta$ S of the following reaction.

A) positive
B) negative
C) no change

Answer 2

negative

Question 3

Which of the following is the enthalpy change of the following reaction under standard conditions?

A) -8 kJ/mol
B) +8 kJ/mol
C) -506 kJ/mol
D) +63 kJ/mol

Answer 3

-8 kJ/mol

Question 4

You are working in a research laboratory and have developed a new reagent that cleaves C-H bonds homolytically. Unfortunately, this reagent can achieve only one of the transformations shown below. In light of bond dissociation energies, which transformation is most likely to be achieved?

A)
B)
C)
D)

Question 5

What type of bond cleavage does the following reaction involve?

Question 6

Predict the sign of $\Delta$ S of the following reaction.

Question 7

Estimate the enthalpy change of the following reaction under standard conditions.

Question 8

Later in the course, we will compare the halogenation of differently substituted carbons, comparing reactions like the ones below. Which of the following statements is true about reactions A and B?

A) Both reactions have a positive heat of reaction ( $\Delta$ H^o)
B) Neither reaction has a positive heat of reaction ( $\Delta$ H^o)
C) Only reaction A has a positive heat of reaction ( $\Delta$ H^o)
D) Only reaction B has a positive heat of reaction ( $\Delta$ H^o)

Question 9

Estimate the enthalpy change of the following reaction under standard conditions.

Question 10

Predict the sign of $\Delta$ G for an endothermic reaction with an increase in entropy.

A) positive
B) negative
C) no change
D) cannot predict without additional information

Question 11

Predict the sign of $\Delta$ S of the following reaction.

Question 12

Of following reactions, which one(s) would you expect to have a negative $\Delta$ S?

A)
B)
C)
D)

Question 13

Later in the course, we will compare the halogenation of differently substituted carbons, comparing reactions like the ones below. Which of the following reactions has a more exothermic heat of reaction ( $\Delta$ H^o)?

A) Reaction A has a more exothermic heat of reaction ( $\Delta$ H^o)
B) Reaction B has a more exothermic heat of reaction ( $\Delta$ H^o)
C) Both reactions have the same heat of reaction ( $\Delta$ H^o)

Question 14

Which of the following would you expect to have the most negative $\Delta$ S?

A)
B)
C)
D)

Question 15

Why is the entropy change negative for ring closures?

A) Closing a ring results in fewer molecules.
B) Closing a ring results in more molecules.
C) Closing a ring releases energy.
D) Closing a ring restricts the rotation around individual carbon-carbon bonds.

Question 16

Predict the sign of $\Delta$ G for an exothermic reaction with an increase in entropy.

A) positive
B) negative
C) no change
D) cannot predict without additional information

Question 17

Which of the following is the enthalpy change of the following reaction under standard conditions?

A) -8 kJ/mol
B) +8 kJ/mol
C) +222 kJ/mol
D) +79 kJ/mol

Question 18

What type of bond cleavage does the following reaction involve?

A) homolytic
B) heterolytic

Question 19

Predict the sign of $\Delta$ S of the following reaction.

A) positive
B) negative
C) no change

Question 20

Estimate the enthalpy change of the following reaction under standard conditions.

Question 21

Based on the following energy diagram, is the reaction exothermic or endothermic?

Question 22

What is the energy of activation for the following reaction?

Question 23

Does a reaction with a $\Delta$ H of 20 kJ/mol and a $\Delta$ S of 10 J/mol K at 298 K favor reactants or products?

Question 24

Given the following rate law, what is the order of the reaction with respect to MeI?

Question 25

Predict the sign of $\Delta$ G for an exothermic reaction with a decrease in entropy.

A) positive
B) negative
C) no change
D) cannot predict without additional information

Question 26

Does a reaction with a K_eq = 10 favor reactants or products?

Question 27

Based on the following energy diagram, is the reaction exothermic or endothermic?

Question 28

Given the following rate law, what is the order of the reaction with respect to sodium cyanide?

Question 29

Does a reaction with a negative $\Delta$ G favor reactants or products?

Question 30

Predict the sign of $\Delta$ G for an endothermic reaction with a decrease in entropy.

A) positive
B) negative
C) no change
D) cannot predict without additional information

Question 31

What is the effect of a catalyst on a reaction?

A) It increases the rate.
B) It decreases the entropy.
C) It changes the equilibrium.
D) It makes the products more stable.

Question 32

Given the following rate law, what is the order of the reaction with respect to tert-butyl iodide?

Question 33

Which of the following describes the effect of a catalyst on a reaction?

A) It lowers the free energy of the products.
B) It makes the reactants less stable.
C) It changes the equilibrium constant.
D) It lowers the energy of activation.

Question 34

Does a reaction with a positive $\Delta$ S and a negative $\Delta$ H favor reactants or products?

Question 35

Which of the following is an energy diagram for a three-step reaction?

A)
B)
C)
D)

Question 36

Does a reaction with a $\Delta$ H of 14 kJ/mol and a $\Delta$ S of 150 J/molK at 298 K favor reactants or products?

Question 37

Does a reaction with a positive $\Delta$ G favor reactants or products?

Question 38

Does a reaction with a positive $\Delta$ S and a positive $\Delta$ H favor reactants or products?

Question 39

What is the energy of activation for the following reaction?

Question 40

Which of the following is an energy diagram for a two-step reaction?

A)
B)
C)
D)

Question 41

Identify the electrophilic site in the following molecule.

Question 42

Identify the electrophilic site in the following molecule.

Question 43

Which of the following energy diagrams shows a concerted endothermic reaction?

A)
B)
C)
D)

Question 44

Which of the following energy diagrams shows the reaction with the smallest energy of activation?

A)
B)
C)
D)

Question 45

Draw an energy diagram for a concerted exothermic reaction.

Question 46

Identify the nucleophilic site in the following molecule.

Question 47

Identify the nucleophilic centers in the following molecule.

Question 48

Identify the electrophilic site in the following molecule.

A) H
B) C of carbonyl
C) C other than carbonyl
D) O of carbonyl

Question 49

What is an intermediate?

A) A local maximum on the energy diagram.
B) A point on the reaction pathway that has a discrete lifetime.
C) A point half-way between the starting materials and products.
D) The highest energy compound on an energy diagram.

Question 50

Draw an energy diagram for a three-step reaction.

Question 51

Identify the nucleophilic site(s) in the following molecule.

Question 52

Identify the nucleophilic atom in the following molecule.

A) P
B) C
C) H
D) Me

Question 53

What is a transition state?

A) An isolable intermediate in a reaction.
B) The starting materials of the reaction.
C) A local maximum on the energy diagram.
D) A low-energy point between the starting materials and the product.

Question 54

Identify the electrophilic site in the following molecule.

Question 55

Identify the electrophilic site in the following molecule.

A) C
B) O
C) B
D) No electrophilic site

Question 56

Which of the following energy diagrams is of a reaction with one transition state?

A)
B)
C)
D)

Question 57

Which of the following cannot be a nucleophile?

A)
B)
C)
D)

Question 58

Draw an energy diagram for an endothermic reaction with two steps.

Question 59

Which of the following energy diagrams is of a reaction with one intermediate?

A)
B)
C)
D)

Question 60

Identify the nucleophilic site in the following molecule.

Question 61

Which of the following mechanistic steps represents the loss of a leaving group?

A)
B)
C)
D)

Question 62

Which of the following cannot be an electrophile?

A)
B)
C)
D)

Question 63

Melphalan, a drug used in chemotherapy, reacts with itself in the body before binding with its target, as illustrated in the mechanism below. Which two patterns of arrow pushing are seen in this reaction?

Question 64

The following reaction has three mechanistic steps. Identify the pattern of arrow pushing steps in each step.

Question 65

Identify the sequence of curved arrows (electron movement) in the steps of the following reaction.

A) Proton transfer, proton transfer
B) Proton transfer, loss of leaving group
C) Nucleophilic attack, proton transfer
D) Proton transfer, nucleophilic attack

Question 66

Which of the following is the most stable cation?

A)
B)
C)
D)

Question 67

For the following reaction step, indicate which pattern of arrow pushing it represents.

A) Proton transfer
B) Loss of leaving group
C) Nucleophilic attack
D) Rearrangement

Question 68

Which of the following is hydride?

A) H⁺
B) H
C) H⁻
D) H₂

Question 69

For the following reaction step, indicate which pattern of arrow pushing it represents.

Question 70

For the following reaction step, indicate which pattern of arrow pushing it represents.

A) Proton transfer
B) Loss of leaving group
C) Nucleophilic attack
D) Rearrangement

Question 71

For the following reaction step, indicate which pattern of arrow pushing it represents.

A) Proton transfer
B) Loss of leaving group
C) Nucleophilic attack
D) Rearrangement

Question 72

Melphalan, a drug used in chemotherapy, reacts with itself before binding with its target in the body, as illustrated below. Draw in the curved arrows that account for this transformation.

Question 73

What is wrong with the following mechanism?

A) There is no leaving group, so there should be no arrows.
B) The arrow should be removing a proton from the H₂O group.
C) An arrow is also needed to indicate the loss of the leaving group.
D) The arrow indicating the formation of the C-Br bond (nucleophilic attack) should start at the bromide anion.

Question 74

For the following reaction step, indicate which pattern of arrow pushing it represents.

A) Proton transfer
B) Loss of leaving group
C) Nucleophilic attack
D) Rearrangement

Question 75

For the following reaction step, indicate which pattern of arrow pushing it represents.

A) Proton transfer
B) Loss of leaving group
C) Nucleophilic attack
D) Rearrangement

Question 76

Which of the following mechanistic steps represents a nucleophilic attack?

A)
B)
C)
D)

Question 77

The following reaction has three mechanistic steps. Draw all curved arrows necessary to complete the mechanism.

Question 78

What is wrong with the following mechanism?

A) There is no leaving group, so there should be no arrows.
B) The arrow should be removing a proton from the H₂O group.
C) An arrow is also needed to indicate the loss of the leaving group.
D) The arrow is backwards.

Question 79

Draw the structure of hydride.

Question 80

For the following reaction step, indicate which pattern of arrow pushing it represents.

A) Proton transfer
B) Loss of leaving group
C) Nucleophilic attack
D) Rearrangement