Deck 6: Chemical Reactivity and Mechanisms

Question 1

Predict the sign of ∆S for the following reaction. SHAPE \* MERGEFORMAT

A) positive
B) negative
C) no change

Answer 1

positive

Question 2

Using Table 6.1, estimate the enthalpy change of the following reaction under standard conditions.

Answer 2

+8 kJ/mol

Question 3

Predict the sign of ∆S for the following reaction.

A) positive
B) negative
C) no change

Answer 3

negative

Question 4

What type of bond cleavage does the following reaction involve?

A) homolytic
B) heterolytic
C) covalent
D) ionic

Question 5

Which of the following would you expect to have the most negative ∆S?

A)
B)
C)
D)

Question 6

Using Table 6.1, estimate the enthalpy change of the following reaction under standard conditions.

Question 7

Predict the sign of ∆S for the following reaction.

Question 8

What type of bond cleavage does the following reaction involve?

Question 9

Predict the sign of ∆S for the following reaction.

Question 10

Using Table 6.1, estimate the enthalpy change of the following reaction under standard conditions.

Question 11

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 I and II?

A) Both reactions have a positive heat of reaction (∆H^o)
B) Neither reaction has a positive heat of reaction (∆H^o)
C) Only reaction I has a positive heat of reaction (∆H^o)
D) Only reaction II has a positive heat of reaction (∆H^o)

Question 12

Using Table 6.1, 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

Question 13

Predict the sign of ∆S for the following reaction.

A) positive
B) negative
C) no change

Question 14

In a heterolytic bond cleavage, ____ are formed.

A) ions
B) radicals
C) only cations
D) only anions

Question 15

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 16

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 (∆H^o)?

A) Reaction I has a more exothermic heat of reaction (∆H^o)
B) Reaction II has a more exothermic heat of reaction (∆H^o)
C) Both reactions have the same heat of reaction (∆H^o)

Question 17

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 18

Using Table 6.1, which of the following is the enthalpy change of the following reaction under standard conditions?

A) -21 kJ/mol
B) +21 kJ/mol
C) -171 kJ/mol
D) +171 kJ/mol

Question 19

In a homolytic bond cleavage, ____ are formed.

A) ions
B) radicals
C) only cations
D) only anions

Question 20

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

A) I
B) II
C) III
D) IV
E) I and II

Question 21

Does a reaction with a positive ∆S and a positive ∆H favor reactants or products?

Question 22

What is the energy of activation for the following reaction?

Question 23

Does a reaction with a ∆H of 14 kJ/mol and a ∆S of 150 J/mol·K at 298 K favor reactants or products?

Question 24

Predict the sign of ∆G for an exothermic reaction with a decrease in entropy.

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

Question 25

Predict the sign of ∆G for an endothermic 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 ∆H of 20 kJ/mol and a ∆S of 10 J/mol·K at 298 K favor reactants or products?

Question 27

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

Question 28

What is the energy of activation for the following reaction?

Question 29

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

Question 30

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

Question 31

Does a reaction with a value of 0 for ∆G favor reactants or products?

Question 32

Predict the sign of ∆G for an exothermic reaction with an increase in entropy.

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

Question 33

Does a reaction with a positive ∆G favor reactants or products?

Question 34

Which of the following indicates a reaction with a negative ∆G?

A) endergonic, spontaneous
B) endergonic, not spontaneous
C) exergonic, spontaneous
D) exergonic, not spontaneous

Question 35

Predict the sign of ∆G for an endothermic reaction with an increase in entropy.

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

Question 36

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

Question 37

Does a reaction with a positive ∆S and a negative ∆H favor reactants or products?

Question 38

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

Question 39

Which of the following indicates a reaction with a positive ∆G?

A) endergonic, spontaneous
B) endergonic, not spontaneous
C) exergonic, spontaneous
D) exergonic, not spontaneous

Question 40

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

Question 41

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

A)
B)
C)
D)

Question 42

Identify the electrophilic site in the following molecule.

Question 43

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

A)
B)
C)
D)

Question 44

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 45

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

Question 46

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

A)
B)
C)
D)

Question 47

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 48

What is an intermediate?

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

Question 49

Identify the nucleophilic site in the following molecule.

Question 50

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 51

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

A)
B)
C)
D)

Question 52

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

Question 53

Identify the nucleophilic centers in the following molecule.

Question 54

Draw an energy diagram for an exothermic three-step reaction.

Question 55

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

A)
B)
C)
D)

Question 56

Draw an energy diagram for a concerted exothermic reaction.

Question 57

Identify the nucleophilic site in the following molecule.

Question 58

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

A)
B)
C)
D)

Question 59

Identify the electrophilic site in the following molecule, CH₃CH₂NHCH₂CH₃.

A) H
B) N
C) CH₂
D) CH₃
E) there is no electrophilic site

Question 60

Identify the nucleophilic atom in the following molecule, Me₃P.

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

Question 61

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 62

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 63

Which of the following mechanistic steps represents a nucleophilic attack?

A) I
B) II
C) III
D) IV

Question 64

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 65

Which of the following is the most stable cation?

A) I
B) II
C) III
D) IV

Question 66

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 67

Identify the electrophilic site in the following molecule.

Question 68

Which of the following is hydride?

A) H⁺
B) H
C) H⁻
D) H₂

Question 69

Identify the electrophilic site in the following molecule.

Question 70

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 71

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

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

Question 72

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 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

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

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

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 77

What pattern of curved arrow pushing is the second step of this reaction?

A) proton transfer
B) loss of leaving group
C) nucleophilic attack
D) rearrangement

Question 78

What pattern of curved arrow pushing is the fourth step of this reaction?

A) proton transfer
B) loss of leaving group
C) nucleophilic attack
D) rearrangement

Question 79

Identify the electrophilic site in the following molecule.

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

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