Deck 6: Ionic Reactions - Nucleophilic Substitution and Elimination Reactions of Alkyl Halides

Question 1

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

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

Answer 1

I

Question 2

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.

Answer 2

It would double the rate.

Question 3

The reaction, has the following thermodynamic values at 27ºC: $\Delta$ 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

Answer 3

-91.6 kJ mol^-1

Question 4

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

A) Decreases the energy of activation.
B) Increases the total number of collisions between reactants.
C) Decreases the rate of the reverse reaction.
D) Favors endothermic processes.
E) None of the above properly explains the observed increase in reaction rates with increase in temperature.

Question 5

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 6

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 the above
E) None of the above

Question 7

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 8

Consider the S_N2 reaction of butyl bromide with OH^- ion. CH₃CH₂CH₂CH₂Br + OH^- $\rightarrow$ 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.

Question 9

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

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

Question 10

For the typical S_N2 reaction Y^- + RX $\rightarrow$ RY + X^-
It can be predicted that $\Delta$ S^‡ will be:

A) positive.
B) zero.
C) negative.
D) either positive or negative.
E) unpredictable as to algebraic sign.

Question 11

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

Question 12

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 CH₃CO₂- 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.

Question 13

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 14

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

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

Question 15

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 16

The hybridization state of the charged carbon in a carbocation is

A) sp⁴
B) sp³
C) sp²
D) sp
E) s

Question 17

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 18

Select the rate law for the following reaction,e.g. , CH₃CH₂CH₂CHBrCH₃ + OH ^- $\rightarrow$ CH₃CH₂CH₂CHOHCH₃ + X ^-
( 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

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 CN- 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.

Question 20

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

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

Question 21

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 22

The p orbital of a methyl cation,CH₃⁺,contains how many electrons?

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

Question 23

By analyzing the starting material and the product(s),the following reaction is an example of what type of mechanism?

A) S_N1
B) S_N2
C) E1
D) E2
E) More than one of the above

Question 24

By analyzing the starting material and the product(s),the following reaction is an example of what type of mechanism?

A) S_N1
B) S_N2
C) E1
D) E2
E) None of the above

Question 25

Which is the strongest nucleophile?

A) OH^-
B) CH₃CH₂O^-
C)

D) CH₃CH₂OH
E) H₂O

Question 26

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 27

By analyzing the starting material and the product(s),the following reaction is an example of what type of mechanism?

A) S_N1
B) S_N2
C) E1
D) E2
E) None of the above

Question 28

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 29

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

A)

B)

C)

D)

E)

Question 30

Which is a true statement concerning the transition state of the rate-determining step of an S_N1 reaction?

A) Structurally,it closely resembles the carbocation intermediate.
B) Both covalent bond-breaking and bond-making are occurring.
C) Formation of the transition state is an exothermic reaction.
D) Necessarily,the transition state has zero charge overall.
E) More than one of the above.

Question 31

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 32

You want to synthesize 3-methyl-2-pentene from 2-chloro-3-methylpentane.Which reagent would you use?

A) HCl,heat
B) NH₃(aq),25^oC
C) CH₃CO₂Na,CH₃CO₂H,heat
D) CH₃CH₂ONa,CH₃CH₂OH,heat
E) CH₃CH₂OH,heat

Question 33

Which of the following reactions proceeds with inversion of configuration at the carbon bearing the leaving group?

A) S_N2
B) S_N1
C) E2
D) E1
E) All of these

Question 34

The Hammond-Leffler postulate,when applied to nucleophilic substitutions and elimination reactions,states that:

A) a negatively-charged nucleophile is stronger than its conjugate acid.
B) polar aprotic solvents strongly accelerate the rate of S_N2 processes.
C) bimolecular nucleophilic substitutions are 2^nd order kinetically.
D) the transition state for an endergonic reaction step (one accompanied by an increase in free energy)resembles the product of that step.
E) elimination reactions will always compete with nucleophilic substitution reactions.

Question 35

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

A) An S_N2 reaction would take place with inversion of configuration at the stereogenic center.
B) An S_N1 reaction would take place with retention of configuration at the stereogenic center.
C) An S_N1 reaction would take place with racemization of configuration at the stereogenic center.
D) An S_N1 reaction would take place,accompanied by an E1 reaction,affording a complex mixture of products.
E) An E2 reaction would take place,during which the stereogenic center is lost.

Question 36

By analyzing the starting material and the product(s),the following reaction is possibly an example of what type of mechanism?

A) S_N1
B) S_N2
C) E1
D) E2
E) More than one of the above

Question 37

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 38

Consider the substitution reaction that takes place when (R)-3-iodo-3-methylheptane is treated with sodium acetate (CH₃CO₂Na).Which of the following would be true?

A) An S_N2 reaction would take place with inversion of configuration at the stereogenic center.
B) An S_N1 reaction would take place with retention of configuration at the stereogenic center.
C) An S_N1 reaction would take place with racemization of configuration at the stereogenic center.
D) An S_N1 reaction would take place,accompanied by an E1 reaction,affording a complex mixture of products.
E) An E2 reaction would take place,during which the stereogenic center is lost.

Question 39

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

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

Question 40

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

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

Question 41

Which of the following is the poorest leaving group?

A) H ^-
B) CH₃O ^-
C) H₂O
D) OH ^-
E) NH₂ ^-

Question 42

Which is the weakest nucleophile in polar protic solvents?

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

Question 43

Which S_N2 reaction would take place most rapidly?

A)

B)

C)

D)

E)

Question 44

Identify the leaving group in the following reaction:

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

Question 45

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) They would all react at the same rate.

Question 46

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 47

Which of the following is not a good leaving group?

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

Question 48

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

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

Question 49

Which nucleophilic substitution reaction would be unlikely to occur?

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

Question 50

Which is the weakest nucleophile in polar aprotic solvents?

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

Question 51

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

Question 52

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

A) I^-
B) Br^-
C) Cl^-
D) F^-
E) These are all equal.

Question 53

Which of the following is a feasible substitution reaction?

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

Question 54

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

A) F^-
B) Cl^-
C) Br^-
D) I^-
E) They are all equally reactive.

Question 55

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

Question 56

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

A)

B)

C)

D)

E)

Question 57

Identify the leaving group in the following reaction.

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

Question 58

Which is not a polar aprotic solvent?

A)

B)

C)

D)

E)

Question 59

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 60

Which is a polar aprotic solvent?

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

Question 61

By analyzing the starting material and the product(s),the following reaction is possibly an example of what type of mechanism?

A) S_N1
B) S_N2
C) E1
D) E2
E) None of the above

Question 62

What would be the major product(s)of the following reaction?

A) I
B) II
C) III
D) IV
E) None of the above

Question 63

Elimination reactions are favored over nucleophilic substitution reactions:

A) at high temperatures.
B) when tert-butoxide ion is used.
C) when 3 $\degree$ alkyl halides are used as substrates.
D) when nucleophiles are used which are strong bases and the substrate is a 2 $\degree$ alkyl halide.
E) in all of these cases.

Question 64

What would you expect to be the chief organic product(s)when tert-butyl bromide reacts with sodium acetylide,i.e. ,

A) I
B) II
C) III
D) IV
E) None of these

Question 65

What would be the major product of the following reaction?

A) I
B) II
C) III
D) IV
E) Equal amounts of I and III

Question 66

The major product(s)of the following reaction is(are):

A) I
B) II
C) III
D) IV
E) Equal amounts of I and II

Question 67

Which alkyl halide,when treated with sodium ethoxide in ethanol,would afford a product mixture consisting of more than one elimination product?

A) 1-bromo-3,3-dimethylpentane
B) 1-bromo-2,3-dimethylpentane
C) 2-bromo-3,4-dimethylpentane
D) 2-bromo-3,3-dimethylpentane
E) None of the above would yield more than one elimination product.

Question 68

By analyzing the starting material and the product,the following reaction is possibly an example of what type of mechanism(s)?

A) S_N1
B) S_N2
C) E1
D) E2
E) More than one of the above

Question 69

What would be the major product(s)of the following reaction?

A) I
B) II
C) III
D) IV
E) More than one of the above

Question 70

What would be the major product(s)of the following reaction?

A) I
B) II
C) III
D) IV
E) None of the above

Question 71

What major product(s)are likely to be obtained from the following reaction?

A) I,by predominantly S_N2
B) II,by predominantly S_N2
C) An equimolar mixture of I and II,by predominantly S_N1.
D) III,by substitution of the alkyl group,rather than substitution of the chloro group.
E) Actually,none of these products are likely to be obtained as major products,because elimination will probably predominate,leading to the formation of an alkene.

Question 72

Reaction of sodium ethoxide with 1-bromopentane at 30 $\degree$ C yields primarily:

A) CH₃CH₂CH₂CH=CH₂
B) CH₃CH₂CH=CHCH₃
C) CH₃CH₂CH₂CH₂CH₃
D) CH₃CH₂CH₂CH₂CH₂OH
E) CH₃CH₂CH₂CH₂CH₂OCH₂CH₃

Question 73

What would be the major product(s)of the following reaction?

A) I
B) II
C) III
D) IV
E) None of the above

Question 74

The product(s)for the following reaction would mainly be dictated by which mechanism?

A) S_N1
B) S_N2
C) E1
D) E2
E) None of the above

Question 75

By analyzing the starting material and the product(s)the following reaction is an example of what type of mechanism?

A) S_N1
B) S_N2
C) E1
D) E2
E) None of the above

Question 76

Which nucleophilic substitution reaction is not likely to occur?

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

Question 77

Heating an alcoholic solution of sodium hydroxide and 1-bromopentane at 60 $\degree$ C yields primarily:

A)

B)

C)

D)

E)

Question 78

What would be the major product(s)of the following reaction?

A) I
B) II
C) III
D) IV
E) None of the above

Question 79

What would be the major product of the following reaction?

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

Question 80

What would you expect to be the chief organic product(s)when 2-bromo-2-methylpentane react(s)with sodium propynide,i.e. ,

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