Deck 6: Nucleophilic Reactions

Question 1

An increase in the temperature at which a reaction is carried out increases

A)the collision frequency.
B)the fraction of molecules with proper orientation.
C)the fraction of molecules with energy greater than E_act.
D)More than one of these choices.
E)None of these choices.

Answer 1

More than one of these choices.

Question 2

Select the potential energy diagram that represents a two-step endothermic (endergonic)reaction.

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

Answer 2

II

Question 3

Consider the S_N2 reaction of butyl bromide with OH^- ion. CH₃CH₂CH₂CH₂Br + OH^- $\to$ CH₃CH₂CH₂CH₂OH + Br^-
Assuming no other changes,what effect on the rate would result from simultaneously doubling the concentrations of both butyl bromide and OH- ion?

A)No effect.
B)It would double the rate.
C)It would triple the rate.
D)It would increase the rate four times.
E)It would increase the rate six times.

Answer 3

It would increase the rate four times.

Question 4

The rate equation for a nucleophilic substitution reaction of a tertiary alkyl bromide (R-Br)with I^- ion would be:

A)Rate = k [RBr]
B)Rate = k [I^-]
C)Rate = k [RBr][I^-]
D)Rate = k [RBr]²[I^-]
E)Rate = k [RBr][I^-]²

Question 5

Consider the S_N2 reaction of 2-iodopentane with CH₃CO₂- ion.
Assuming no other changes,what effect on the rate would result from simultaneously doubling the concentrations of both 2-iodopentane and sodium acetate?

A)No effect.
B)It would double the rate.
C)It would triple the rate.
D)It would increase the rate four times.
E)It would increase the rate six times.

Question 6

The reaction, has the following thermodynamic values at 27.0 ºC: $\Delta$ H = -75.3 kJ mol^-1; $\Delta$ S = 54.4 J K^-1 mol^-1.What is the value of $\Delta$ G for this reaction?

A)-73.8 kJ mol^-1
B)-76.8 kJ mol^-1
C)-59.0 kJ mol^-1
D)+91.6 kJ mol^-1
E)-91.6 kJ mol^-1

Question 7

If the rate of reaction of [0.1 M] sodium cyanide with [0.1 M] 2-bromo-2-methylpropane is 1.2 x 10^-3 M/s,what would be the effect on the overall rate if the concentration of sodium cyanide is increased to [0.2 M] and the concentration of the alkyl bromide is decreased to [0.05 M]?

A)the rate will increase by a factor of 2
B)the rate will decrease by a factor of 2
C)the rate will increase by a factor of 10
D)the rate will decrease by a factor of 10
E)the rate will remain unchanged

Question 8

The difference in the bond energies of reactants and the transition state of a reaction is designated by the notation:

A)" $\Delta$ H ^$\circ$ "
B)" $\Delta$ H^‡"
C)" $\Delta$ G ^$\circ$ "
D)" $\Delta$ G^‡"
E)" $\Delta$ S^‡"

Question 9

The hybridization state of the charged carbon in a carbocation is ___.

A)sp⁴
B)sp³
C)sp²
D)sp
E)s

Question 10

The rate equation for a nucleophilic substitution reaction of a secondary alkyl chloride (R-Cl)with I^- ion would be:

A)Rate = k [RCl]
B)Rate = k [I^-]
C)Rate = k [RCl][I^-]
D)Rate = k [RCl]²[I^-]
E)Rate = k [RCl][I^-]²

Question 11

Which will be true for any actual or potential nucleophilic substitution reaction?

A)" $\Delta$ H ^$\circ$ is positive."
B)" $\Delta$ H ^$\circ$ is negative."
C)" $\Delta$ G^‡ is positive."
D)" $\Delta$ G ^$\circ$ is positive."
E)" $\Delta$ G ^$\circ$ is negative."

Question 12

A true statement about the transition state(s)of an S_N2 reaction is:

A)The two transition states are of unequal energy.
B)The transition states precede and follow an unstable reaction intermediate.
C)The single transition state represents the point of maximum free energy of the reaction.
D)Existence of this transition state implies an exothermic reaction.
E)The transition state will always have a net charge of -1.

Question 13

Consider the reaction of 2-chloro-2-methylpentane with sodium iodide. Assuming no other changes,how would it affect the rate if one simultaneously doubled the concentration of 2-chloro-2-methylpentane and sodium iodide?

A)No effect.
B)It would double the rate.
C)It would triple the rate.
D)It would quadruple the rate.
E)It would increase the rate five times.

Question 14

The major product of the following reaction would be:

A)I
B)II
C)III
D)IV
E)An equimolar mixture of I and II.

Question 15

Select the potential energy diagram that represents a single-step endothermic (endergonic)reaction.

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

Question 16

Increasing the temperature of a chemical reaction usually increases greatly the rate of the reaction.The most important reason for this is that increasing the temperature

A)increases the collision frequency.
B)decreases the probability factor.
C)increases the fraction of collisions with energy greater than E_act.
D)decreases the energy of activation.
E)makes the reaction more exothermic.

Question 17

What product(s)would you expect to obtain from the following S_N2 reaction?

A)I
B)II
C)An equimolar mixture of I and II.
D)III
E)None of these choices.

Question 18

Select the rate law for the following reaction,e.g., CH₃CH₂CH₂CHBrCH₃ + OH^- $\to$ CH₃CH₂CH₂CHOHCH₃ + Br ^-
( RBr )

A)Rate = k [RBr]
B)Rate = k [RBr] [OH^-]
C)Rate = k [RBr]² [OH^-]
D)Rate = k [RBr] [OH^-]²
E)Rate = k [RBr]² [OH^-]²

Question 19

Select the potential energy diagram that represents an exothermic (exergonic)reaction.

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

Question 20

Consider the S_N2 reaction of 1-chloro-5-methylhexane with CN- ion.
Assuming no other changes,what effect on the rate would result from simultaneously doubling the concentrations of both 1-chloro-5-methylhexane and NaCN?

A)No effect.
B)It would double the rate.
C)It would triple the rate.
D)It would increase the rate four times.
E)It would increase the rate six times.

Question 21

Ambident nucleophiles are ones which can react with a substrate at either of two nucleophilic sites.Which of the following is not an ambident nucleophile?

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

Question 22

Rank the following in terms of nucleophilic strength:

A)I>II>III>IV>V
B)V>IV>III>II>I
C)I>IV>II>III>V
D)V>I>IV>II>III
E)I>II>IV>V>III

Question 23

Which is the weakest nucleophile in polar aprotic solvents?

A)I^-
B)Br^-
C)Cl^-
D)F^-
E)All of these choices are equally strong nucleophiles,regardless of the type of solvent used.

Question 24

An increase in the kinetic energy of reacting molecules results in

A)a decrease in reaction rate.
B)an increase in the probability factor.
C)a decrease in the probability factor.
D)an increase in the reaction rate.
E)no changes.

Question 25

Reaction of (R)-2-chloro-4-methylhexane with excess NaI in acetone gives racemic 2-iodo-4-methylhexane.What is the explanation that best describes this transformation?

A)an S_N2 reaction has occurred with inversion of configuration
B)racemization followed by an S_N2 attack
C)an S_NI reaction has taken over resulting in inversion of configuration
D)an S_N1 reaction has occurred due to carbocation formation
E)an S_N1 reaction followed by an S_N2 "backside" attack

Question 26

Which alkyl halide would you expect to undergo an S_N2 reaction most slowly?

A)1-bromohexane
B)1-bromo-2-methylpentane
C)1-bromo-3-methylpentane
D)1-bromo-4-methylpentane
E)1-bromo-2,2-dimethylbutane

Question 27

Which S_N2 reaction would you expect to take place most rapidly? Assume that the concentrations of the reactants and the temperature are the same in each instance.

A)
B)

C)
D)

E)

Question 28

Identify the nucleophile in the following reaction: 2 H₂O + RX $\to$ ROH + H₃O⁺ + X^-

A)X-
B)H₃O⁺
C)ROH
D)H₂O
E)RX

Question 29

The p orbital of the charged carbon in the isopropyl cation,(CH₃)₂CH⁺,contains how many electrons?

A)0
B)1
C)2
D)3
E)4

Question 30

Which is not a polar aprotic solvent?

A)
B)
C)
D)
E)

Question 31

Which is the weakest nucleophile in polar protic solvents?

A)I^-
B)Br^-
C)Cl^-
D)F^-
E)All of these choices are equally strong nucleophiles,regardless of the type of solvent used.

Question 32

Which alkyl chloride,though primary,is essentially unreactive in S_N2 reactions?

A)
B)

C)

D)
E)

Question 33

Which ion is the strongest nucleophile in aqueous solution?

A)F^-
B)Cl^-
C)Br^-
D)I^-
E)All of these choices are equally strong.

Question 34

Consider the substitution reaction that takes place when (R)-3-bromo-3-methylhexane is treated with methanol.Which of the following would be true?

A)The reaction would take place only with inversion of configuration at the stereogenic center.
B)The reaction would take place only with retention of configuration at the stereogenic center.
C)The reaction would take place with racemization.
D)No reaction would take place.
E)The alkyl halide does not possess a stereogenic center.

Question 35

Which of the following is not a nucleophile?

A)H₂O
B)CH₃O^-
C)NH₃
D)NH₄⁺
E)All are nucleophiles.

Question 36

Which of the following alkyl bromide isomers would most readily undergo an S_N2 reaction?

A)bromocyclobutane
B)4-bromo-1-butene
C)3-bromo-1-butene
D)1-bromo-1-butene
E)All will react at the same rate.

Question 37

Which is the strongest nucleophile?

A)OH^-
B)CH₃CH₂O^-
C)
D)CH₃CH₂OH
E)H₂O

Question 38

Which alkyl halide would be most reactive in an S_N1 reaction?

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

Question 39

Which is a polar aprotic solvent?

A)2-methylhexane
B)CCl₄
C)NH₃(l)
D)CH₃CH₂CH₂OCH₂CH₂CH₃
E)2-methyl-2-propanol

Question 40

Identify the nucleophile in the following reaction: 2R'OH + RX $\to$ ROR' + [R'OH₂]⁺ + X^-

A)X^-
B)[R'OH₂]^-
C)ROR'
D)R'OH
E)RX

Question 41

Which of the following would be most reactive in an S_N2 reaction?

A)
B)
C)
D)
E)

Question 42

Identify the leaving group in the following reaction.

A)C₆H₅S^-
B)Na⁺
C)CH₃CH₂I
D)C₆H₅SCH₂CH₃
E)I^-

Question 43

Which S_N2 reaction would take place most rapidly?

A)
B)
C)
D)
E)

Question 44

Which of the following nucleophiles will react the fastest with 1-bromoptopane in ethanol?

A)SH^-
B)OH^-
C)H₂O
D)H₂S
E)All react at about the same rate.

Question 45

Which of the following is a feasible substitution reaction?

A)CH₃CH₂Cl + NaBr $\to$ CH₃CH₂Br + NaCl
B)CH₃CH₃ + NaCN $\to$ CH₃CH₂CN + NaH
C)CH₃CH₂Cl + NaOH $\to$ CH₂=CH₂ + H₂O + NaCl
D)More than one of these choices.
E)None of these choices.

Question 46

Which S_N2 reaction will occur most rapidly in aqueous acetone solution? Assume concentrations and temperature are the same in each instance.

A)HO^- + CH₃-Cl $\to$ CH₃OH + Cl^-
B)HO^- + CH₃CH₂-Cl $\to$ CH₃CH₂OH + Cl^-
C)HO^- + (CH₃)₂CH-Cl $\to$ (CH₃)₂CHOH + Cl^-
D)HO^- + (CH₃)₃C-Cl $\to$ (CH₃)₃COH + Cl^-
E)HO^- + (CH₃)₃CCH₂-Cl $\to$ (CH₃)₃CCH₂OH + Cl^-

Question 47

Which S_N2 reaction will occur most rapidly in a mixture of water and ethanol?

A)I^- + CH₃CH₂-Br $\to$ CH₃CH₂-I + Br^-
B)I^- + CH₃CH₂-Cl $\to$ CH₃CH₂-I + Cl^-
C)I^- + CH₃CH₂-F $\to$ CH₃CH₂-I + F^-
D)Br^- + CH₃CH₂-Cl $\to$ CH₃CH₂-Br + Cl^-
E)Br^- + CH₃CH₂-F $\to$ CH₃CH₂-Br + F^-

Question 48

Which of the following is the poorest leaving group?

A)H^-
B)CH₃O^-
C)H₂O
D)OH^-
E)NH₂^-

Question 49

Which of the following solvents will best promote a nucleophilic reaction between NaCN and 1-bromopropane?

A)H₂O/MeOH mixture
B)H₂O
C)MeCN
D)HF(aq)
E)running with no solvent

Question 50

The relative nucleophilicities of species do not necessarily parallel the relative basicities of the same species because

A)not all nucleophiles are bases,and vice versa.
B)experimental measurements of sufficient accuracy are not available to make the comparisons.
C)nucleophilicity is a thermodynamic matter; basicity is a matter of kinetics.
D)basicity is a thermodynamic matter; nucleophilicity is a matter of kinetics.
E)Actually,the relative values do parallel one another.

Question 51

Which of the following nucleophiles will react the fastest with tert-butyl bromide in ethanol?

A)F^-
B)Br^-
C)I^-
D)Cl^-
E)All react at about the same rate.

Question 52

Which alkyl halide would you expect to react most slowly when heated in aqueous solution?

A)(CH₃)₃C-F
B)(CH₃)₃C-Cl
C)(CH₃)₃C-Br
D)(CH₃)₃C-I
E)All of these choices would react at the same rate.

Question 53

Identify the leaving group in the following reaction.

A)CH₃OH
B)CH₃OH₂⁺
C)CH₃OCH₃
D)H₂O
E)None of these choices.

Question 54

Which is the most reactive nucleophile in DMF (structure shown below)?

A)F^-
B)Cl^-
C)Br^-
D)I^-
E)All of these choices are equally reactive.

Question 55

Which ion is the strongest nucleophile in an aprotic solvent such as dimethylsulfoxide?

A)I^-
B)Br^-
C)Cl^-
D)F^-
E)All of these choices are equal.

Question 56

Which nucleophilic substitution reaction would be unlikely to occur?

A)HO^- + CH₃CH₂-I $\to$ CH₃CH₂-OH + I^-
B)I^- + CH₃CH₂-H $\to$ CH₃CH₂-I + H^-
C)CH₃S^- + CH₃-Br $\to$ CH₃S-CH₃ + Br^-
D)All of these choices would be unlikely to occur.
E)None of these choices would be unlikely to occur.

Question 57

Considering the relative solvation of reactants and the transition states of substitution reactions of these reactants,predict which general type of reaction would be most favored by the use of a polar solvent.

A)Y: + RX $\to$ RY⁺ + X:^-
B)Y:^- + RX $\to$ RY + X:^-
C)Y: + RX⁺ $\to$ RY⁺ + X:
D)Y:^- + RX⁺ $\to$ RY + X:
E)RX⁺ $\to$ R⁺ + X:

Question 58

Which of these species,acting in a protic solvent,exhibits greater nucleophilic activity than expected on the basis of its basicity?

A)OH^-
B)CH₃O^-
C)SH^-
D)Cl^-
E)H₂O

Question 59

Which of the following is not true concerning the strength of a nucleophile?

A)Nucleophilicity may not parallel basicity.
B)Negatively charged nucleophiles are always more reactive than their conjugate acids.
C)The greater the strength of a nucleophile,the faster an S_N2 reaction will occur.
D)Strong bases are always good nucleophiles
E)None of these answer choices are correct.

Question 60

Which of the following is not a good leaving group?

A)C₂H₅O^-
B)Cl^-
C)Isup>-
D)CH₃CO₂^-
E)All of these choices are good leaving groups.

Question 61

In the S_N2 reaction,the unstable arrangement of atoms in which both the nucleophile and the leaving group are partially bonded to the same carbon atom is called the ___.

Question 62

S_N2 reactions of the type,Nu^- + RL $\to$ Nu-R + L^-, are favored

A)when tertiary substrates are used.
B)by using a high concentration of the nucleophile.
C)by using a solvent of high polarity.
D)by the use of weak nucleophiles.
E)by none of these choices.

Question 63

S_N1 reactions of the following type: Nu:^- + R-X $\to$ R-Nu + :X^-
Are favored

A)by the use of tertiary substrates (as opposed to primary or secondary substrates).
B)by increasing the concentration of the nucleophile.
C)by increasing the polarity of the solvent.
D)by use of a weak nucleophile.
E)by the use of tertiary substrates (as opposed to primary or secondary substrates)and by use of a weak nucleophile.

Question 64

As we go down Group 7A of the periodic table,the size of the halogen atom increases; accordingly,the carbon-halogen bond length gets ___ and the bond strength gets ___.

Question 65

In order for colliding species to react,they must ___ and ___.

Question 66

Racemic mixtures form in S_N1 reactions when leaving group departure results in a loss of chirality followed by subsequent attack of the nucleophile.

Question 67

Which of the following statements is (are)true of an S_N2 reaction of (R)-2-bromobutane with hydroxide ion?

A)Doubling the hydroxide ion concentration would double the rate of the reaction.(Assume that all other experimental conditions are unchanged.)
B)The major product would be (S)-2-butanol.
C)Doubling the concentration of (R)-2-bromobutane would double the rate of the reaction.(Assume that all other experimental conditions are unchanged.)
D)All of these choices.
E)Two of these choices.

Question 68

S_N1 reactions of the type,Nu^- + RL $\to$ Nu-R + L^-,are favored

A)when tertiary substrates are used.
B)by using a high concentration of the nucleophile.
C)when L^- is a strong base.
D)by use of a non-polar solvent.
E)by none of these choices.

Question 69

What final product is likely to be obtained through the following series of reactions?

Question 70

Which of the following statements is (are)true of S_N1 reactions of alkyl halides in general?

A)The rate of an S_N1 reaction depends on the concentration of the alkyl halide.
B)The rate of an S_N1 reaction depends on the concentration of the nucleophile.
C)S_N1 reactions of alkyl halides are favored by polar solvents.
D)The rate of an S_N1 reaction depends on the concentration of the alkyl halide and S_N1 reactions of alkyl halides are favored by polar solvents.
E)The rate of an S_N1 reaction depends on the concentration of the alkyl halide and the concentration of the nucleophile,and S_N1 reactions of alkyl halides are favored by polar solvents.

Question 71

S_N1 reactions of the following type: Nu:^- + R-X $\to$ R-Nu + :X^-
Are favored

A)by the use of tertiary substrates (as opposed to primary or secondary substrates).
B)by increasing the concentration of the nucleophile.
C)by increasing the polarity of the solvent.
D)by use of a strong base.
E)by more than one of these choices.

Question 72

Which of the following statements is (are)true of S_N1 reactions of alkyl halides in general?

A)The rate of an S_N1 reaction depends on the concentration of the alkyl halide.
B)The rate of an S_N1 reaction depends on the concentration of the nucleophile.
C)S_N1 reactions of alkyl halides occur faster in polar aprotic solvents (compared to protic solvents).
D)The rate of an S_N1 reaction depends on the concentration of the alkyl halide and S_N1 reactions of alkyl halides occur faster in polar aprotic solvents (compared to protic solvents).
E)The rate of an S_N1 reaction depends on the concentration of the alkyl halide and the concentration of the nucleophile,and S_N1 reactions of alkyl halides occur faster in polar aprotic solvents (compared to protic solvents).

Question 73

Increasing the temperature of a reaction will speed up the overall rate as this will increase the energy of activation for reaction.

Question 74

Which nucleophilic substitution reaction is not likely to occur?

A)I^-+ CH₃CH₂-Cl $\to$ CH₃CH₂-I + Cl^-
B)I^- + CH₃CH₂-Br $\to$ CH₃CH₂-I + Br^-
C)I^- + CH₃CH₂-OH $\to$ CH₃CH₂-I + OH^-
D)CH₃O^-+ CH₃CH₂-Br $\to$ CH₃CH₂-OCH₃ + Br^-
E)OH^-+ CH₃CH₂-Cl $\to$ CH₃CH₂-OH + Cl^-

Question 75

Draw the potential energy diagram that represents an exothermic reaction between a tertiary alkyl halide and methanol.Briefly explain your rationale.

Question 76

When 5-bromo-1-pentanol is treated with sodium hydride in diethyl ether,the product is analyzed to be C₅H₁₀O.Propose a likely structure for this product,suggesting a reasonable mechanistic pathway for its formation.

Question 77

In a highly exergonic S_N2 reaction we can assume the transition state is similar to the products formed in the reaction.

Question 78

A nucleophile in an S_N2 reaction must approach from the ___ of the carbon atom attached to the leaving group since the electrons in the nucleophile's HOMO begins to overlap with the ___ of the carbon atom attached to the leaving group.

Question 79

Which nucleophilic substitution reaction would be likely to occur (although probably not in excellent yield,due to competing elimination)?

A)HO^- + CH₃CH₂CH₂CHICH₃ $\to$ CH₃ CH₂CH₂CHOHCH₃ + I^-
B)Cl^-+ CH₃CH₂CH₂CH₂-OH $\to$ CH₃CH₂CH₂CH₂-Cl + OH^-
C)CH₃S^- + CH₃CH₂CH₂-OCH₃ $\to$ CH₃S-CH₂CH₂CH₃ + OCH₃-^--
D)All of these choices are likely to occur.
E)None of these choices are likely to occur.

Question 80

An endergonic S_N2 reaction will have a have a higher energy of activation ( $\Delta$ G^‡)than an exergonic S_N2 reaction.