Package title: Solomons Test Bank Course Title: Solomons 11e Chapter Number: 6
Question type: Multiple choice
1) Select the rate law for the following reaction, e.g., CH3CH2CH2CHBrCH3 + OH 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 Answer: B Topic: Reaction kinetics Section: 6.5 Difficulty Level: Easy
2) 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 Ans: C Topic: Reaction Kinetics Section: 6.5 Difficulty Level: Easy
3) Consider the S N2 reaction of butyl bromide with OH- ion. CH3CH2CH2CH2Br + OH- CH3CH2CH2CH2OH + Br Assuming no other changes, what effect on the rate would result from simultaneously doubling 1
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. Ans: D Topic: Reaction kinetics Section: 6.5 Difficulty Level: Medium
4) Consider the S N2 reaction of 2-iodopentane with CH3CO2 ion.
O
O
I
O
NaI
ONa
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. Ans: D Topic: Reaction kinetics Section: 6.5 Difficulty Level: Medium
5) Consider the S N2 reaction of 1-chloro-5-methylhexane with CN ion.
Cl
NaCN NaCN
CN
NaCl NaCl
Assuming no other changes, what effect on the rate would result from simultaneously doubling the concentrations of both 1-chloro-5-methylhexane and NaCN?
2
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. Ans: D Topic: Reaction kinetics Section: 6.5 Difficulty Level: Medium
4) Consider the S N2 reaction of 2-iodopentane with CH3CO2 ion.
O
O
I
O
NaI
ONa
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. Ans: D Topic: Reaction kinetics Section: 6.5 Difficulty Level: Medium
5) Consider the S N2 reaction of 1-chloro-5-methylhexane with CN ion.
Cl
NaCN NaCN
CN
NaCl NaCl
Assuming no other changes, what effect on the rate would result from simultaneously doubling the concentrations of both 1-chloro-5-methylhexane and NaCN?
2
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. Ans: D Topic: Reaction kinetics Section: 6.5 Difficulty Level: Medium
6) The reaction, CH3Cl + OH
H2O
CH3OH +
Cl
has the following thermodynamic values at 27.0 ºC: H = -75.3 kJ mol-1; -1 -1 S = 54.4 J K mol . What is the value of 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 Ans: E Topic: Free energy changes Sections: 6.7 Difficulty Level: Easy
7) Select the potential energy diagram that represents an exothermic (exergonic) reaction.
3
A) I B) II C) III D) IV E) V Ans: E Topic: Free energy diagrams Section: 6.7 Difficulty Level: Easy
8) Select the potential energy diagram that represents a single-step endothermic (endergonic) reaction.
A) I 4
B) II C) III D) IV E) V Ans: A Topic: Free energy diagrams Section: 6.7 Difficulty Level: Easy
9) Select the potential energy diagram that represents a two-step endothermic (endergonic) reaction.
A) I B) II C) III D) IV E) V Ans: B Topic: Free energy diagrams Section: 6.7 Difficulty Level: Easy
10) The difference in the bond energies of reactants and the transition state of a reaction is designated by the notation:
5
A) H B) H‡ C) G D) G‡ E) S‡ Ans: B Topic: Free energy diagrams Section: 6.7 Difficulty Level: Easy
11) 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 Eact. D) More than one of these choices. E) None of these choices. Ans: D Topic: Activation energy Section: 6.7 Difficulty Level: Medium
12) Which will be true for any actual or potential nucleophilic substitution reaction? A) H is positive. B) H is negative. C) G‡ is positive. D) G is positive. E) G is negative. Ans: C Topic: Transition state theory Section: 6.7 Difficulty Level: Medium
13) 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
6
A) increases the collision frequency. B) decreases the probability factor. C) increases the fraction of collisions with energy greater than Eact. D) decreases the energy of activation. E) makes the reaction more exothermic. Ans: C Topic: Activation Energy Section: 6.7 Difficulty Level: Easy
14) What product(s) would you expect to obtain from the following S N2 reaction? H
H
CH3ONa
?
CH3
Br
CH3OH
H
H
H
OCH3
CH3
OCH3
CH3
H
I
CH3O
H
Br
H
II
III
A) I B) II C) An equimolar mixture of I and II. D) III E) None of these choices. Ans: B Topic: Predicting products Section: 6.8 Difficulty Level: Easy
15) The major product of the following reaction would be:
7
CH2Cl
OH H
OCH3
?
S N2
CH3
CH2OH H3CO
H
CH2OH H
CH3
CH3
II
I
CH2Cl
CH2Cl HO
OCH3
H
H
OH
CH3
CH3
III
IV
A) I B) II C) III D) IV E) An equimolar mixture of I and II. Ans: B Topic: Predicting products Section: 6.8 Difficulty Level: Easy
16) 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 uns table 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 c harge of -1. Ans: C Topic: Generalities Sections: 6.7 and 6.8 Difficulty Level: Hard
17) The rate equation for a nucleophilic substitution reaction of a tertiary alkyl bromide (R-Br) with I ion would be:
8
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 Ans: A Topic: Reaction Kinetics Section: 6.9 and 6.10 Difficulty Level: Easy
18) Consider the reaction of 2-chloro-2-methylpentane with sodium iodide. NaI
NaCl
Cl
I
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. Ans: B Topic: Reaction Kinetics Section: 6.9 and 6.10 Difficulty Level: Hard
19) 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 Ans: B 9
Topic: Reaction kinetics Section: 6.9 and 6.10 Difficulty Level: Medium
20) The hybridization state of the charged carbon in a carbocation is ___. A) sp4 B) sp3 C) sp2 D) sp E) s Ans: C Topic: Carbocations Section: 6.11 Difficulty Level: Easy
21. The p orbital of a methyl cation, CH3+, contains how many electrons? A) 0 B) 1 C) 2 D) 3 E) 4 Ans: A Topic: Carbocations Section: 6.11 Difficulty Level: Easy
22) 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 Ans: A 10
Topic: Carbocations Section: 6.11 Difficulty Level: Easy
23) 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 answer choices are correct. Ans: A Topic: Stereochemistry of SN/E reactions Sections: 6.8 and 6.12 Difficulty Level: Easy
24) 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. Ans: C Topic: Predicting mechanism, stereochemistry of SN reactions Sections: 6.8 and 6.12 Difficulty Level: Medium
25) 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 11
mixture of products. E) An E2 reaction would take place, during which the stereogenic center is lost. Ans: E Topic: Predicting mechanism, stereochemistry of SN reactions Sections: 6.8 and 6.12 Difficulty Level: Medium
26) Consider the substitution reaction that takes place when (R)-3-iodo-3-methylheptane is treated with sodium acetate (CH3CO2 Na). 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. Ans: D Topic: Predicting mechanism, stereochemistry of SN reactions Sections: 6.8 and 6.12 Difficulty Level: Medium
27) By analyzing the starting material and the product(s), the following reaction is an example o f what type of mechanism?
A) S N1 B) S N2 C) E1 D) E2 E) More than one of these choices. Ans: B Topic: Predicting mechanisms, products Section: 6.13 Difficulty Level: Easy
12
28) By analyzing the starting material and the product(s), the following reaction is an example o f what type of mechanism?
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: B Topic: Predicting mechanisms, products Section: 6.13 Difficulty Level: Easy
29) 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 these choices. Ans: A Topic: Predicting mechanisms, products Section: 6.13 Difficulty Level: Easy
30) 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. 13
C) bimolecular nucleophilic substitutions are 2nd 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. Ans: D Topic: Hammond-Leffler postulate Section: 6.13 Difficulty Level: Easy
31) When 1,4-diiodo-2,2-dimethylbutane (0.10 mol) is treated with 0.10 mol of NaCN in dimethyl sulfoxide at 30C, the product formed is: I NC
A) CN I
B)
CN NC
C) I
D) Ans: B Topic: Predicting mechanisms, products Section: 6.13 Difficulty Level: Medium
32) 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 these choices. Ans: A 14
Topic: Hammond-Leffler postulate Section: 6.13 Difficulty Level: Medium
33) By analyzing the starting material and the product(s), the following reaction is possibly an example of what type of mechanism?
+ Br
N3
N3
A) S N1 B) S N2 C) E1 D) E2 E) More than one of these choices. Ans: A Topic: Predicting mechanisms, products Section: 6.13 Difficulty Level: Hard
34) 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. Ans: B Topic: Synthesis, reagent selection Section: 6.13 Difficulty Level: Hard
35) You want to synthesize 3-methyl-2-pentene from 2-chloro-3-methylpentane. Which reagent would you use? A) HCl, heat B) NH3(aq), 25oC C) CH3CO2 Na, CH3CO2H, heat 15
D) CH3CH2ONa, CH3CH2OH, heat E) CH3CH2OH, heat Ans: D Topic: Synthesis, reagent selection Section: 6.13 Difficulty Level: Hard
36) Which alkyl chloride, though primary, is essentially unreactive in S N2 reactions? Cl
A)
B) Cl
C) Cl
Cl
D)
Cl
E) Ans: E Topic: Steric hindrance Sections: 6.13 Difficulty Level: Easy
37) Which alkyl halide would be most reactive in an S N1 reaction?
16
Br Br
Br
I
II
III
Br Br
IV
V
A) I B) II C) III D) IV E) V Ans: D Topic: Kinetics Section: 6.13 Difficulty Level: Easy
38) Reaction of (R)-2-chloro-4-methylhexane with excess NaI in acetone gives racemic 2-iodo4-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 Ans: D Topic: Kinetics and Mechanism Section: 6.8, 6.13 Difficulty Level: Easy
39) 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. 17
E) no changes. Ans: D Topic: Transition State theory Sections: 6.7 and 6.13 Difficulty Level: Medium
40) 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 Ans: E Topic: Kinetics Sections: 6.8 and 6.13 Difficulty Level: Medium
41) Identify the nucleophile in the following reaction: 2 H2O + RX
ROH + H3O+ + X
A) XB) H3O+ C) ROH D) H2O E) RX Ans: D Topic: Generalities, nucleophiles Sections: 6.3 and 6.13 Difficulty Level: Easy
42) Which of the following is not a nucleophile? A) H2O B) CH3OC) NH3 18
D) NH4+ E) All are nucleophiles. Ans: D Topic: Generalities, nucleophiles Sections: 6.3 and 6.13 Difficulty Level: Easy
43) 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? 2 .. .. .. OCH CH S : : :CN: 2 2.. :OH .. .. I
II
III
O N::O : .. ..
H.. .. .. N:O :H .. .. H
IV
V
..
..
:
A) I B) II C) III D) IV E) V Ans: B Topic: Nucleophiles Sections: 6.3 and 6.13 Difficulty Level: Easy
44) Identify the nucleophile in the following reaction: 2R’OH + RX
ROR’ + [R’OH2]+ + X-
A) X B) [R’OH2] C) ROR’ D) R’OH E) RX Ans: D 19
Topic: Generalities, nucleophiles Sections: 6.3 and 6.13 Difficulty Level: Medium
45) Which is the strongest nucleophile? A) OHB) CH3CH2O-
C) D) CH3CH2OH E) H2O Ans: B Topic: Nucleophiles Sections: 6.3 and 6.13 Difficulty Level: Medium
46) Rank the following in terms of nucleophilic stren gth:
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 Ans: C Topic: Nucleophiles Sections: 6.3 and 6.13 Difficulty Level: Medium
47) 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) CH3S
+
CH3I
CH3SCH3 +
20
I
B) H
CH3SH +
CH3I
C) CH3O
+
S H3C
CH3I
CH3
+
I
CH3OCH3 +
I
D) H
CH3OH +
E) CH3S
CH3I
+
O H3C
CH3Cl
CH3
CH3SCH3 +
Ans: A Topic: Nucleophilicity, leaving groups Sections: 6.3, 6.8, 6.13 Difficulty Level: Medium
48) Which is not a polar aprotic solvent? O C
A)
H3C
B)
H3C
CH3
C
N
O S
C)
H3C
CH3
O C H
CH3
N
CH3
D)
CH3 CH
E)
H3C
OH
Ans: E Topic: Generalities, solvent effects 21
+
I
Cl
Section: 6.13 Difficulty Level: Easy
49) Which is a polar aprotic solvent? A) 2-methylhexane B) CCl4 C) NH3(l) D) CH3CH2CH2OCH2CH2CH3 E) 2-methyl-2-propanol Ans: D Topic: Generalities, solvent effects Section: 6.13 Difficulty Level: Easy
50) Consider an S N2 reaction of NaSH in a polar aprotic solvent with (CH3)2CHCH2CH2X. What would be the relative order of reactivity for the following X substituents? I. X = I II. X = Br III. X = Cl IV X = F a) I > II > III > IV b) II > I > IV > III c) IV > III > II > I d) III > I > II > IV e) None of these choices. Topic: Generalities, solvent effects Section: 6.13 Difficulty Level: Easy
51) Which is the weakest nucleophile in polar aprotic solvents? A) IB) Br C) ClD) FE) All of these choices are equally strong nucleophiles, regardless of the type of solvent used. Ans: A Topic: Generalities, solvent effects 22
Sections: 6.13 Difficulty Level: Easy
52) Which is the weakest nucleophile in polar protic solvents? A) IB) Br C) ClD) FE) All of these choices are equally strong nucleophiles, regardless of the type of solvent used. Ans: D Topic: Generalities, solvent effects Sections: 6.13 Difficulty Level: Easy
53) Which ion is the strongest nucleophile in aqueous solution? A) FB) ClC) Br D) IE) All of these choices are equally strong. Ans: D Topic: Generalities, solvent effects Sections: 6.13 Difficulty Level: Easy
54) Which ion is the strongest nucleophile in an aprotic solvent such as dimethylsulfoxide? A) IB) Br C) ClD) FE) All of these choices are equal. Ans: D Topic: Nucleophile, solvent effects Sections: 6.13 23
Difficulty Level: Medium
55) 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. Ans: A Topic: Leaving groups Sections: 6.4 and 6.13 Difficulty Level: Easy
56) 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 b y the use of a polar solvent. A) Y: + RX RY+ + X:B) Y:- + RX RY + X:C) Y: + RX+ RY+ + X: D) Y:- + RX+ RY + X: E) RX+ R + + X: Ans: A Topic: Generalities, solvent effects Sections: 6.13 Difficulty Level: Medium
57) Which is the most reactive nucleophile in DMF (structure shown below)? O H
C
N
CH3
CH3
-
A) F B) ClC) Br D) IE) All of these choices are equally reactive. Ans: A 24
Topic: Nucleophile, solvent effects Sections: 6.3, 6.13 Difficulty Level: Easy
58) Which of these species, acting in a protic solvent, exhibits greater nucleophilic activity than expected on the basis of its basicity? A) OHB) CH3OC) SHD) ClE) H2O Ans: C Topic: Nucleophile, solvent effects Sections: 6.3, 6.13 Difficulty Level: Medium
59) Which S N2 reaction will occur most rapidly in a mixture of water and ethanol? A) I- + CH3CH2 – Br CH3CH2 – I + Br B) I- + CH3CH2 – Cl CH3CH2 – I + ClC) I- + CH3CH2 – F CH3CH2 – I + FD) Br - + CH3CH2 – Cl CH3CH2 – Br + ClE) Br - + CH3CH2 – F CH3CH2 – Br + FAns: A Topic: Leaving groups, nucleophiles Sections: 6.3, 6.13 Difficulty Level: Medium
60) Which S N2 reaction will occur most rapidly in aqueous acetone solution? Assume concentrations and temperature are the same in each instance. A) HO- + B) HO- + C) HO- + D) HO- + E) HO- +
CH3-Cl CH3OH + ClCH3CH2-Cl CH3CH2OH + Cl(CH3)2CH-Cl (CH3)2CHOH + Cl(CH3)3C-Cl (CH3)3COH + Cl(CH3)3CCH2-Cl (CH3)3CCH2OH + Cl-
Ans: A 25
Topic: Predicting mechanism, kinetics Sections: 6.3, 6.13 Difficulty Level: Medium
61) The relative nucleophilicities of species do no t 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. Ans: D Topic: Nucleophilicity Sections: 6.3, 6.13 Difficulty Level: Hard
62) 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. Ans: D Topic: Nucleophilicity Sections: 6.3, 6.13 Difficulty Level: Hard
63) 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
26
Ans: C Topic: Predicting mechanism, solvent effects Sections: 6.3, 6.13 Difficulty Level: Medium
64) Which of the following nucleophiles will react the fastest with tert -butyl bromide in ethanol? a) F b) Br c) Id) Cle) All react at about the same rate. Ans: E Topic: Predicting mechanism, kinetics, solvent effectsh Sections: 6.3, 6.13 Difficulty Level: Hard
65) Which of the following nucleophiles will react the fastest with 1-bromoptopane in ethanol? a) SH b) OHc) H2O d) H2S e) All react at about the same rate. Ans: A Topic: Predicting mechanism, nucleophilicity, solvent effects Sections: 6.3, 6.13 Difficulty Level: Medium
66) Which S N2 reaction would take place most rapidly? H2O OH + CH3Cl CH3OH + Cl o 25 C A) O
B) C)
H3C
H2O +
O
+
O
H2O
CH3Cl
CH3Cl
o
25 C
H2O o
25 C
H3CO
CH3
CH3OH2
27
+
Cl
+
Cl
H
CH3OH +
CH3OH o 25 C
CH3Cl
D)
E)
SH
+
H2O
CH3Cl
o
25 C
+
O H3C
CH3
CH3SH +
Cl
Cl
Ans: E Topic: Kinetics, nucleophilicity Sections: 6.3, 6.8, 6.13 Difficulty Level: Medium
67) Which of the following is a feasible substitution reaction? A) CH3CH2Cl + NaBr CH3CH2Br + NaCl B) CH3CH3 + NaCN CH3CH2CN + NaH C) CH3CH2Cl + NaOH CH2=CH2 + H2O + NaCl D) More than one of these choices. E) None of these choices. Ans: A Topic: Leaving group Sections: 6.2, 6.4, 6.13 Difficulty Level: Easy
68) Identify the leaving group in the following reaction.
S Na
S
Na
I
A) C6H5SB) Na+ C) CH3CH2I D) C6H5SCH2CH3 E) IAns: E Topic: Generalities, leaving group Sections: 6.4 and 6.13 Difficulty Level: Easy
28
+
I
69) Identify the leaving group in the following reaction. CH3OH + CH3OH2
CH3OCH3 + H2O H
A) CH3OH B) CH3OH2+ C) CH3OCH3 D) H2O E) None of these choices. Ans: D Topic: Leaving groups Sections: 6.4 and 6.13 Difficulty Level: Easy
70) Which nucleophilic substitution reaction would be unlikel y to occur? A) HO + CH3CH2 – I CH3CH2 – OH + I B) I + CH3CH2 – H CH3CH2 – I + H C) CH3S + CH3 – Br CH3S – CH3 + Br D) All of these choices would be unlikely to occur. E) None of these choices would be unlikely to occur. Ans: B Topic: Leaving groups Sections: 6.4 and 6.13 Difficulty Level: Easy
71) Which of the following would be most reactive in an S N2 reaction? Br
A) B)
Br
C)
Br Br
D)
29
E)
Br
Ans: D Topic: Leaving groups Sections: 6.4 and 6.13 Difficulty Level: Easy
72) Which of the following is the poorest leaving group? A) H B) CH3O C) H2O D) OH E) NH2 Ans: E Topic: Generalities, leaving group Sections: 6.4 and 6.13 Difficulty Level: Medium
73) Which of the following is not a good leaving group? A) C2H5O B) Cl C) I D) CH3CO2 E) All of these choices are good leaving groups. Ans: A Topic: Leaving groups Sections: 6.4 and 6.13 Difficulty Level: Medium
74) Which nucleophilic substitution reaction is not likely to occur? A) I + CH3CH2 – Cl CH3CH2 – I + Cl B) I + CH3CH2 – Br CH3CH2 – I + Br C) I + CH3CH2 – OH CH3CH2 – I + OH 30
D) CH3O + CH3CH2 – Br CH3CH2 – OCH3 + Br E) OH + CH3CH2 – Cl CH3CH2 – OH + Cl Ans: C Topic: Leaving groups Sections: 6.3, 6.4, 6.13 Difficulty Level: Medium
75) By analyzing the starting material and the product, the following reaction is possibly an example of what type of mechanism(s)?
+ Cl
A) S N1 B) S N2 C) E1 D) E2 E) More than one of the above Ans: E Topic: Predicting mechanisms, products Section: 6.18 Difficulty Level: Medium
76) Which mechanism best describes the chemical process shown below?
a) S N2 b) E1 c) E2 d) S N1 e) None of these choices. Ans: B Topic: Predicting mechanisms, products Section: 6.18 31
Difficulty Level: Medium
77) By analyzing the starting material and the product(s), the following reaction is an example o f what type of mechanism? Br
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: D Topic: Predicting mechanisms, products Section: 6.18 Difficulty Level: Medium
78) By analyzing the starting material and the product(s), the following reaction is possibly an example of what type of mechanism?
HO
O
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: E Topic: Predicting mechanisms, products Sections: 6.13 and 6.18 Difficulty Level: Hard
79. 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 32
B) 1-bromo-2,3-dimethylpentane C) 2-bromo-3,4-dimethylpentane D) 2-bromo-3,3-dimethylpentane E) None of these choices would yield more than one elimination product. Ans: C Topic: Predicting products Section: 6.18 Difficulty Level: Medium
80) Elimination reactions are favored over nucleophilic substitution reactions A) at high temperatures. B) when tert-butoxide ion is used. C) when 3 alkyl halides are used as substrates. D) when nucleophiles are used which are strong bases and the substrate is a 2 alkyl halide. E) in all of these cases. Ans: E Topic: Generalities Section: 6.18 Difficulty Level: Medium
81) What would you expect to be the chief organic product(s) when tert-butyl bromide reacts with sodium acetylide, i.e., Br HC
I
C:
?
Na
II
III
HC
CH
IV
A) I B) II C) III D) IV 33
E) None of these choices. Ans: D Topic: Predicting mechanisms, products Section: 6.15 and 6.18 Difficulty Level: Hard
82) What would you expect to be the chief organic product(s) when 2-bromo-2-methylpentane react(s) with sodium propynide, i.e., Br C:
I
?
Na
II
HC
IV
III
CH
HC
CH
V
A) I B) II C) III D) IV E) V Ans: D Topic: Predicting mechanisms, products Section: 6.15 and 6.18 Difficulty Level: Hard
83) Suggest a reagent to perform the following transformation:
34
a) NaOH, H2O b) NaH, THF c) NaOMe, MeOH d) t-butoxide, t-butanol e) Ethanol Ans: D Topic: Predicting reagents for mechisms Section 6.15 and 6.18 Difficulty: Medium
84) What major product(s) are likely to be obtaine d from the following reaction? H
Cl
H
CH3CH2ONa CH3CH2OH,
H
O
H
I
?
65oC
H
O
O
H
H
H
Cl
II
III
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. Ans: E Topic: Predicting mechanisms, products Section: 6.18 Difficulty Level: Medium
85) The major product(s) of the following reaction is(are):
35
H
H
CH3
NaI, CH3CH2OH 25oC
Cl
H
H
H
I
CH3
I
CH3
H
I
CH3
II
III
H
H
CH3
OCH2CH3
IV
A) I B) II C) III D) IV E) Equal amounts of I and II. Ans: B Topic: Predicting mechanisms, products Section: 6.8 and 6.18 Difficulty Level: Easy
86) What would be the major product of the following reaction? CH2Cl H
CH3
OH
S N2
CH2OH H3C
CH2OH H
H
CH3
II
I
CH2Cl HO
CH3
III
CH2Cl H
OH
IV
A) I B) II C) III D) IV E) An equimolar mixture of I and II. 36
Ans: B Topic: Predicting products Section: 6.8 and 6.18 Difficulty Level: Easy
87) What would be the major product(s) of the following reaction?
CH3CH2CO2 Na CH3CH2CO2H
I
O2CCH2CH3
O2CCH2CH3
I
O2CCH2CH3
II
III
IV
A) I B) II C) III D) IV E) None of these choices. Ans: A Topic: Predicting products Section: 6.8 and 6.18 Difficulty Level: Easy
88) What would be the major product(s) of the following reaction? O O
CH3SNa
S
CH3SH
O
SCH3
I
II
SCH3
III
37
IV
A) I B) II C) III D) IV E) More than one of these choices. Ans: C Topic: Predicting products Section: 6.8 and 6.18 Difficulty Level: Easy
89) What would be the major product(s) of the following reaction? Br
NaI Acetone
I
I
I
I
II
III
A) I B) II C) III D) IV E) None of these choices. Ans: B Topic: Predicting products Sections: 6.8 and 6.18 Difficulty Level: Easy
90) What would be the major product of the following reaction?
38
IV
H
C
Br
25 C
H
H3C
CN
H
H
H3C
o
II CN H
H
Br
H
I H3C
CN
H3C
H
H3C
Br
NC
III
IV
A) I B) II C) III D) IV E) Equal amounts of I and III. Ans: C Topic: Predicting mechanisms, products Sections: 6.8 and 6.18 Difficulty Level: Easy
91) The product(s) for the following reaction would mainly be dictated by which mechanism? NaCN DMF Cl
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: B Topic: Predicting mechanisms, products Sections: 6.8 and 6.18 Difficulty Level: Easy
39
92) Reaction of sodium ethoxide with 1-bromopentane at 30C yields primarily: A) CH3CH2CH2CH=CH2 B) CH3CH2CH=CHCH3 C) CH3CH2CH2CH2CH3 D) CH3CH2CH2CH2CH2OH E) CH3CH2CH2CH2CH2OCH2CH3 Ans: E Topic: Predicting mechanisms, products Sections: 6.8 and 6.18 Difficulty Level: Easy
93) Heating an alcoholic solution of sodium hydroxide and 1-bromopentane at 60C yields primarily: A) B) C) D) E)
OH O
Ans: D Topic: Predicting mechanisms, products Sections: 6.8 and 6.18 Difficulty Level: Medium
94) What would be the major product(s) of the following reaction?
40
O O
S
CF3
NaN3
O
DMF
N3
I
II
III
O
IV
A) I B) II C) III D) IV E) None of these choices. Ans: E Topic: Predicting products Section: 6.8 and 6.18 Difficulty Level: Medium
95) What would be the major product(s) of the following reaction? CH3OH Br
heat
H3CO
I
II
III
A) I and II B) I, II, and III C) III D) I, II, and IV E) None of these choices. 41
IV
N3
Ans: D Topic: Predicting products Section: 6.8 and 6.18 Difficulty Level: Medium
96) Predict the product(s) for the following reaction sequence.
1. NaI, acetone
O F3C
O
S
2. NaCN, DMF
O
A)
B)
CN
C)
CN
D) E) More than one of these choices Ans: C Topic: Synthesis, reagent selection Sections: 6.8 and 6.18 Difficulty Level: Medium
97) Predict the product(s) for the following reaction sequence. 1. NaI, acetone 2. CH3CO 2 Na, CH 3CO 2H
Cl
A)
B)
O
O
42
C)
O
O
D) E) A mixture of two of these choices Ans: C Topic: Synthesis, reagent selection Sections: 6.8 and 6.18 Difficulty Level: Medium
98) When 0.10 mol of ICH2CH2CH2CH2Cl reacts with 0.10 mol of NaOCH3 in CH3OH at 40C, the major product is: A) CH3OCH2CH2CH2CH2Cl B) CH3OCH2CH2CH2CH2I C) CH3OCH2CH2CH2CH2OCH3 D) CH2=CHCH2CH2Cl E) CH2=CHCH2CH2I Ans: A Topic: Predicting mechanisms, products Sections: 6.8 and 6.18 Difficulty Level: Medium
99) If 0.10 mol of HSCH2CH2OH reacts at 25C, sequentially, with 0.20 mol of NaH, 0.10 mol of CH3CH2Br followed by the addition of H2O, which is the major product? A) HSCH2CH2OCH2CH3 B) CH3CH2SCH2CH2OH C) CH3CH2SCH2CH2OCH2CH3 D) CH2=CH2 E) CH3CH3 Ans: B Topic: Predicting mechanisms, products Sections: 6.8 and 6.18 Difficulty Level: Hard 43
100) What would be the major product obtained when trans-1-bromo-3-methylcyclopentane is allowed to react with NaSH at 25oC? H
H3C H
SH
SH
H3C H
H
I
H3C
SH
H3C
H
Br
HS
II
III
H Br
IV
A) I B) II C) III D) IV E) Equal amounts of I and II. Ans: B Topic: Predicting mechanisms, products Sections: 6.8 and 6.18 Difficulty Level: Hard
101) The product(s) for the following reaction would mainly be dictated by which mechanism? Br
CH3SNa EtOH
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: B Topic: Predicting mechanisms, products Sections: 6.8 and 6.18 Difficulty Level: Hard
102) Predict the product(s) for the following reaction sequence. a. NaH, THF OH b. 1-iodopropane
44
O
A) O
B) I
+
OH
C) +
D) E) None of these choices. Ans: A Topic: Synthesis, reagent selection Sections: 6.8 and 6.18 Difficulty Level: Medium
103) S N2 reactions of the type, Nu- + RL 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. Ans: B Topic: Generalities Sections: 6.8, 6.13, 6.18 Difficulty Level: Easy
104) 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. 45
E) Two of these choices. Ans: D Topic: Generalities Sections: 6.8, 6.13, 6.18 Difficulty Level: Medium
105) Which nucleophilic substitution reaction would be likely to occur (although probably not in excellent yield, due to competing elimination)? A) HO + CH3CH2CH2CHICH3 CH3 CH2CH2CHOHCH3 + I B) Cl + CH3CH2CH2CH2 – OH CH3CH2CH2CH2 – Cl + OH C) CH3S + CH3CH2CH2 – OCH3 CH3S – CH2CH2CH3 + OCH3 D) All of these choices are likely to occur. E) None of these choices are likely to occur. Ans: A Topic: Predicting products Sections: 6.8, 6.13, 6.18 Difficulty Level: Medium
106) The major product(s) for the following reaction would mainly be dictated by which mechanism? O O
S
CF3
NaN3
O
CH3CH2OH
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: B Topic: Predicting mechanisms, products Sections: 6.8, 6.13, 6.18 Difficulty Level: Hard 46
107) What would be the major product(s) of the following reaction? Li
Br
I
THF
II
III
A) I B) II C) III D) IV E) More than one of these choices. Ans: A Topic: Predicting products Sections: 6.8, 6.14, 6.18 Difficulty Level: Medium
108) What would be the major product(s) of the following reaction? NaCN I
CN
I
DMSO
C
II
DMSO
III
IV
A) I B) II C) III D) IV E) None of these choices. Ans: E Topic: Predicting products 47
IV
Section: 6.8, 6.14, 6.18 Difficulty Level: Medium
109) Predict the product(s) for the following reaction sequence. Li a. THF, H3C I
b. H2 (excess), Pd/C, EtOH
A) B) C) D) E) None of these choices. Ans: C Topic: Synthesis, reagent selection Sections: 6.8, 6.14, 6.18 Difficulty Level: Medium
110) Predict the product(s) for the following reaction sequence. 1. 1-bromobutane 2. H2 (excess), Pd/C, EtOH
Li
A)
B)
Br
C)
D) E) None of these choices.
48
Ans: E Topic: Synthesis, reagent selection Sections: 6.8, 6.14, 6.18 Difficulty Level: Hard
111) What would be the major product(s) of the following reaction? t -BuOK
-BuOH
t
Cl
t-BuO
I
II
III
IV
A) I B) II C) III D) IV E) More than one of these choices. Ans: D Topic: Predicting products Section: 6.15 and 6.18 Difficulty Level: Easy
112) What would be the major product(s) of the following reaction? O O
CH3CH2ONa
S O
60 oC OCH2CH3
I
II
III
IV
A) I and II B) II and III C) III and IV 49
D) I and IV E) All of these choices. Ans: D Topic: Predicting products Section: 6.16 and 6.18 Difficulty Level: Easy
113) Which of these compounds would give the largest E2/S N2 product ratio on reaction with sodium ethoxide in ethanol at 55°C? Cl
A) B) Cl
C) Cl
Cl
D)
Cl
E) Ans: D Topic: Predicting mechanisms Sections: 6.8, 6.16, 6.18 Difficulty Level: Medium
114) What would be the major product(s) of the following reaction?
-BuOK, t -BuOH
t
Cl
Ot-Bu
I
II
III
50
IV
A) I B) II C) III D) IV E) More than one of these choices. Ans: A Topic: Predicting products Sections: 6.15, 6.16, 6.18 Difficulty Level: Easy
115) The product(s) for the following reaction would mainly be dictated by which mechanism? -BuOK
t
-BuOH
t
Cl
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: D Topic: Predicting mechanisms, products Sections: 6.15, 6.16, 6.18 Difficulty Level: Easy
116) The major product(s) for the following reaction would mainly be dictated by which mechanism? O O
S
CF3 O
CH3CH2OLi CH3CH2OH
A) S N1 B) S N2 C) E1 51
D) E2 E) None of these choices. Ans: D Topic: Predicting mechanisms, products Sections: 6.15, 6.16, 6.18 Difficulty Level: Easy
117) What would be the major product(s) of the following reaction? EtOH, EtONa Cl
EtO
I
II
III
IV
A) I and III B) I and II C) II and III D) IV E) None of these choices. Ans: B Topic: Predicting products Sections: 6.15, 6.16, 6.18 Difficulty Level: Medium
118) What would be the major product(s) of the following reaction?
52
CH3
H3C
CH3O / CH3OH o
55 C
Br
H
CH3
H3C
OCH3
H
OCH3
H3C
CH3
H
I
II
H3C
CH3
III
H3C
IV
A) I B) II C) III and IV D) I and II E) All of these choices. Ans: C Topic: Predicting mechanisms, products Sections: 6.15, 6.16, 6.18 Difficulty Level: Medium
119) What would be the major product(s) of the following reaction? (CH3)2CHONa (CH3)2CHOH Cl 60 oC
OCH(CH3)2
I
II
III
A) I B) II, III, and IV C) III and IV D) II and IV E) IV and III 53
IV
Ans: C Topic: Predicting products Sections: 6.15, 6.16, 6.18 Difficulty Level: Medium
120) The product(s) for the following reaction would mainly be dictated by which mechanism? EtOH, EtONa Cl
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: D Topic: Predicting mechanisms, products Sections: 6.15, 6.16, 6.18 Difficulty Level: Medium
121) Predict the major product(s) for the following reaction sequence. a. NaH, THF OH
Br
b. 60 oC
O
A) A mixture of
O
and
O
B) 54
C)
D) E) A mixture of two of these choices. Ans: E Topic: Synthesis, reagent selection Sections: 6.15, 6.16, 6.18 Difficulty Level: Hard
122) Predict the product(s) for the following reaction sequence. 1. t -BuOK, -BuOK, t -BuOH -BuOH Br
2. H2, Pd/C, EtOH
A) B) Ot-Bu
C) D) E) None of these choices. Ans: A Topic: Synthesis, reagent selection Sections: 6.15, 6.16, 6.18 Difficulty Level: Hard
123) Treating (CH3)3C-Cl with a mixture of H2O and CH3OH at room temperature would yield: A) CH2=C(CH3)2 B) (CH3)3COH C) (CH3)3COCH3 D) All of these choices. 55
E) None of these choices. Ans: D Topic: Predicting mechanisms, products Section: 6.18 Difficulty Level: Medium
124) Treating 1-bromo-1-methylcyclohexane with CH3OH at room temperature would yield:
OCH3
A)
B) C) D) All of these choices. E) None of these choices. Ans: D Topic: Predicting mechanisms, products Section: 6.18 Difficulty Level: Medium
125) Which would be formed in the following reaction? CH3 H3C
Br
CH3OH
?
o
55 C
H
CH3
OCH3 H3C
CH3
H3C
OCH3 H
H
I
II
CH3
CH3
CH3
CH2
III
IV
56
A) I B) II C) III D) IV E) All of these choices. Ans: E Topic: Predicting mechanisms, products Section: 6.18 Difficulty Level: Medium
126) What would be the major product(s) of the following reaction? Br
EtOH 20 oC EtO
OEt
I
II
III
A) I and II B) II and III C) I and III D) IV E) None of these choices. Ans: C Topic: Predicting products Section: 6.12 and 6.18 Difficulty Level: Medium
127) What would be the major product(s) of the following reaction?
57
IV
CH3 Br
CH3CH2CO2H
CH3
room temperature
CH3
O
O
O
O
I
II
III
IV
A) I B) II C) III D) IV E) None of these choices. Ans: D Topic: Predicting products Section: 6.12 and 6.18 Difficulty Level: Medium
128) What would be the major product(s) of the following reaction? HO Br
20 oC
(CH3)2CHCH 2O
(CH3)2CHCH2O
(CH3)2CHCH2O
I
II
III
A) I and II B) I, II, and III C) III D) IV E) None of these choices. Ans: A Topic: Predicting products Sections: 6.12 and 6.18 Difficulty Level: Medium 58
IV
129) When tert-pentyl chloride undergoes solvolysis in aqueous ethanol at room temperature, there is/are formed:
A)
OH
B)
OC2H5
C) D) E) All of these choices. Ans: E Topic: Predicting mechanisms, products Sections: 6.12 and 6.18 Difficulty Level: Medium
130) 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 b y 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 b y polar solvents. Ans: D Topic: Generalities Sections: 6.12, 6.13, 6.18 Difficulty Level: Easy
131) 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. 59
C) S N1 reactions of alkyl halides occur faster in polar aprotic solvents (compa red 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 solve nts (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 po lar aprotic solvents (compared to protic solvents). Ans: A Topic: Generalities Sections: 6.12, 6.13, 6.18 Difficulty Level: Easy
132) S N1 reactions of the type, Nu- + RL 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. Ans: A Topic: Generalities Sections: 6.12, 6.13, 6.18 Difficulty Level: Easy
133) S N1 reactions of the following type: Nu:- + R-X R-Nu + :Xare 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. Ans: A Topic: Generalities Sections: 6.12, 6.13, 6.18 60
Difficulty Level: Medium
134) S N1 reactions of the following type: Nu:- + R-X R-Nu + :Xare 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. Ans: E Topic: Generalities Sections: 6.12, 6.13, 6.18 Difficulty Level: Hard
135) What would be the major product(s) of the following reaction?
CH3CH2OH Br
25 oC
OCH2CH3
I
OCH2CH3
II
III
IV
A) I B) II C) III D) IV E) None of these choices. Ans: E Topic: Predicting products Section: 6.12, 6.14, 6.18 Difficulty Level: Medium 61
136) 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 these choices. Ans: A Topic: Predicting mechanisms, products Sections: 6.12, 6.17, 6.18 Difficulty Level: Easy
137) What would be the major product(s) of the following reaction? (CH3)2CHOH 70 oC
Br
OCH(CH3)2 OCH(CH3)2
I
II
III
A) I B) II C) III D) IV E) None of these choices. Ans: E Topic: Predicting products Sections: 6.14, 6.15, 6.17, 6.18 62
IV
Difficulty Level: Easy
138) What would be the major product(s) of the following reaction? CH3OH Br
OCH3
I
II
III
IV
A) I B) II C) III D) IV E) None of these choices. Ans: E Topic: Predicting products Sections: 6.15, 6.17, 6.18 Difficulty Level: Easy
139) The product(s) for the following reaction would mainly be dictated by which mechanism? 1-pentanol
Cl
80 oC
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: C Topic: Predicting mechanisms, products Sections: 6.15, 6.17, 6.18 Difficulty Level: Easy 63
140) The product(s) for the following reaction would mainly be dictated by which mechanism? O O
S
CF3
CH3CH2OH
O
60 oC
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: C Topic: Predicting mechanisms, products Sections: 6.15, 6.17, 6.18 Difficulty Level: Easy
141) What would be the major product(s) of the following reaction? HO Br
80 oC
(CH3)2CHCH2O
I
II
III
A) I B) II C) III D) IV E) More than one of these choices. Ans: E Topic: Predicting products 64
IV
Sections: 6.15, 6.17, 6.18 Difficulty Level: Medium
142) What would be the major product(s) of the following reaction? (CH3)2CHOH
Cl
70 oC
OCH(CH3)2
I
II
III
IV
A) I B) II and III C) II, III, and IV D) III and IV E) None of these choices. Ans: D Topic: Predicting products Sections: 6.15, 6.17, 6.18 Difficulty Level: Medium
143) What would be the major product(s) of the following reaction?
-BuOH, heat
t
Cl
Ot-Bu
I
II
III
A) I B) II C) III D) IV E) None of these choices. Ans: E 65
IV
Topic: Predicting products Sections: 6.15, 6.17, 6.18 Difficulty Level: Medium
144) 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 these choices. Ans: A Topic: Predicting mechanisms, products Sections: 6.15, 6.17, 6.18 Difficulty Level: Medium
145) Predict the product(s) for the following reaction sequence. 1. EtOH, heat Br
2. H2, Pd/C, EtOH
EtO
A) EtO
B)
C)
D) E) A mixture of two of these choices. Ans: D 66
Topic: Synthesis, reagent selection Sections: 6.15, 6.17, 6.18 Difficulty Level: Medium
146) Which would be the major product of the following reaction? CH3
H
H
CH3
OC(CH3)3
(CH3)3CO
Cl
CH3
?
(CH3)3COH 55oC
H H3C
H3C H
I
H
I
OC(CH3)3
II
III
IV
A) I B) II C) III D) IV E) None of these choices. Ans: C Topic: Predicting mechanisms, products Section: 6.18 Difficulty Level: Easy
147) The product(s) for the following reaction would mainly be dictated by which mechanism?
A) S N1 B) S N2 C) E1 67
D) E2 E) None of these choices. Ans: A Topic: Predicting mechanisms, products Sections: 6.12 and 6.18 Difficulty Level: Hard
148) The product(s) for the following reaction would mainly be dictated by which mechanism?
Br
EtOH heat
A) S N1 B) S N2 C) E1 D) E2 E) None of these choices. Ans: C Topic: Predicting mechanisms, products Sections: 6.15, 6.17, 6.18 Difficulty Level: Hard
149) Which would be formed in the following reaction?
68
O
CH3
OH
Br
H3 C
?
o
50 C
H
O CH3 O
O
O
H3C
CH3
H3C
H
H
I
II
III
IV
A) I B) II C) III D) IV E) All of these choices. Ans: E Topic: Predicting mechanisms, products Section: 6.18 Difficulty Level: Hard
150) Predict the major product(s) for the following reaction sequence. 1. NaI, acetone
Br
2. H2O, 20 oC OH
A) OH
B) C)
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D) E) A 1:1 mixture of two of these choices. ) Ans: E Topic: Synthesis, reagent selection Sections: 6.8, 6.18 then 6.12 Difficulty Level: Hard
151. Predict the product(s) for the following reaction sequence.
OH
A) OD
B)
C) Na
D) E) None of these choices. Ans: B Topic: Synthesis, reagent selection Sections: 6.15, 6.16, 6.18 Difficulty Level: Hard
152) Heating tert-butyl chloride with 1.0 M NaOH in a mixture of water and methanol would yield mainly
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A) (CH3)3COH through an S N1 reaction. B) (CH3)3COCH3 through an S N1 reaction. C) (CH3)3COH through an S N2 reaction. D) (CH3)3COCH3 through an S N2 reaction. E) CH2=C(CH3)2 through an E2 reaction. Ans: E Topic: Predicting mechanism, products Sections: 6.18 Difficulty Level: Hard
Question type: True/false
153) In a highly exergonic S N2 reaction we can assume the transition state is similar to the products formed in the reaction. Ans: False Topic: Hammond Postulate Sections: 6.7 and 6.10 Difficulty Level: Hard
154) An endergonic S N2 reaction will have a have a higher energy of activation (G‡) than an exergonic S N2 reaction. Ans: True Topic: Free energy diagrams Sections: 6.7 and 6.8 Difficulty Level: Medium
155) Increasing the temperature of a reaction will speed up the overall rate as this will increase the energy of activation for reaction. Ans: False Topic: Temperature and rate Section: 6.7 Difficulty Level: Medium
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156) Racemic mixtures form in S N1 reactions when leaving group departure results in a loss of chirality followed by subsequent attack of the nucleophile. Ans: True Topic: S N1 stereochemistry Section: 6.12 Difficulty Level: Medium
157) All S N1 reactions will always be accompanied by a competing E1 reaction. Ans: False Topic: E1 reactions Section: 6.17 Difficulty Level: Medium
Question type: text-entry
158) 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 ___. Ans: longer; weaker Topic: Bond length, bond strength, leaving groups Section: 6.4 Difficulty Level: Easy
159) 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 ___. Ans: transition state Topic: Transition state theory Section: 6.6 Difficulty Level: Easy
160) In order for colliding species to react, they must ___ and ___. Ans: have energy equal/greater than the activation energy, approach with the proper orientation.
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Topic: Activation energy, transition state theory Section: 6.7 Difficulty Level: Medium
161) What final product is likely to be obtained through the following series of reactions?
NaH
OH
Cl
A
B
diethylether O
Ans:
Topic: Multistep synthesis, acid-base reactions, S N2 Sections: 6.8 Difficulty Level: Medium
162) When 5-bromo-1-pentanol is treated with sodium h ydride 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. Ans: The alcohol is likely to be first deprotonated by the strong base, generating an alkoxide ion, which can then undergo intramolecular S N2 reaction to afford the observed product, a cyclic ether. ..
Cl
NaH
OH ..
..
Cl
H2
+
: Na O ..
O
NaCl
Topic: Acid-base reactions, intramolecular S N2 Sections: 6.8 Difficulty Level: Hard
163) Draw the potential energy diagram that represents an exothermic reaction between a tertiary alkyl halide and methanol. Briefly explain your rationale. Ans: The reaction is likely to occur via an S N1 mechanism. The first step is the rate-determining step, leading to the formation of a tertiary carbocation. The second step is a fast step, where the methanol oxygen acts as a nucleophile, attaching to the positively charged carbon, forming a protonated ether; the last step is a fast loss of a proton to form the (uncharged) ether product.
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Energy
time
Topic: Free energy diagrams Sections: 6.7 and 6.10 Difficulty Level: Hard
164) 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. Ans: backside and LUMO Topic: SN2 mechanism Section 6.6 Difficulty Level: Medium
165) The stabilizing effect of alkyl substituents on carbocations can be explained through ___. Ans: hyperconjugation Topic: Carbocation stability Section: 6.11 Difficulty Level: Medium
166) Typically, increasing the concentration of the nucleophile of an S N1 reaction has no impact on the rate of the reaction. The reason for this is that ___. Ans: An S N1 reaction is a multi-step process; the overall reaction rate is det ermined by the rate of formation of the carbocation intermediate. Since the nucleophile is not involved in the ratedetermining step, changes in its concentration typically have no impact on the rate of reaction. Topic: S N1 kinetics Section: 6.12 Difficulty Level: Easy
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167) The substitution mechanism whose rate depends primarily on the relative stability of the intermediate carbocation is the ___. Ans: S N1 Topic: Carbocation stability Sections: 6.11 and 6.12 Difficulty Level: Easy
168) A reaction in which the nucleophile is a molecule of the solvent is referred to as a ___ reaction. Ans: solvolysis Topic: Solvolysis Section: 6.12 Difficulty Level: Easy
169) A student has isolated a chiral alkyl halide (shown below) with a specific rotation of [] = +22.1o. The student decided to store the compound in the solvent MeOH overnight. However, reanalysis of the alkyl halide showed a new chemical formula of C11H16O with a specific rotation of [] = 0o. Suggest a mechanism to justify these results.
Ans: In leaving the compound in MeOH a solvolysis reaction has occurred which results in carbocation formation, following the addition of the MeOH and loss of a proton a racemic mixture is formed which gives a [] = 0o.
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Topic: Solvolysis Sectioin: 6.12 Difficulty Level: Medium
170) The substitution mechanism whose rate depends primarily on the degree of steric hindrance around the leaving group is the ___. Ans: S N2 Topic: Steric hindrance Section: 6.13 Difficulty Level: Medium
171) Increasing the concentration of either of the reactants of an S N2 reaction increases the rate of the reaction. The primary reason for this is that increasing the concentration increases ___. Ans: the frequency of collisions between reactant species, thereb y statistically increasing the chance encounters between species having the requisite Eactivation Topic: Activation energy, kinetics Sections: 6.7 and 6.13 Difficulty Level: Hard
172) The relative nucleophilicity of the halide ion s in polar aprotic solvents is observed to be markedly different from that in protic solvents. Explain briefly. Ans: The smaller, more highly electronegative fluoride ion is more effectively solvated in a protic solvent and is therefore a weaker nucleophile compared to the larger, less electronegative and more polarizable iodide ion. The situation is reversed in aprotic solvents, where the nucleophile is essentially unsolvated; thus, the nucleophilicity parallels the basicity of the halide ions, so that the fluoride ion is the strongest nucleophile of the halide ions. Topic: Nucleophilicity, solvent effects Sections: 6.3 and 6.13 Difficulty Level: Hard
173) Typically alkyl chlorides are slow in S N2 reactions with sodium methoxide in methanol, however the rate of the reaction can be greatly increased with a small addition of NaI. Explain. Ans: The iodide ion will attack the alkyl chloride producing alkyl iodides which are more reactive due to the better iodide leaving group and will allow for ether formation. The iodide ion 76
is regenerated at the end of the reaction making it a catalyst, and thus only a small quantity is needed. R-Cl + I-
Cl- +
+ MeO- R-OMe +
R-I
I-
Topic: Nucleophilicity, solvent effects Sections: 6.3 and 6.13 Difficulty Level: Hard
174) What final product is likely to be obtained through the following series of reactions? NaNH2
Br
A
B
NH3(l)
Ans: Topic: Multistep synthesis, acid-base reactions, S N2 Sections: 6.14 Difficulty Level: Medium
175) What final product is likely to be obtained through the following series of reactions? NaNH2
A
Cl
B
NH3(l)
excess H2 Ni
C
Ans: Topic: Multistep synthesis, acid-base reactions, S N2, hydrogenation Sections: 6.14, 4.16 Difficulty Level: Hard
176) Give a detailed reaction mechanism for the reaction expected to occur when 2-bromo-2methylpentane is heated with methanol. Draw clear structural formulas of all relevant species and use curved arrows to represent electron flow. Also indicate which step is likely to be ratedetermining. Ans: The reaction is likely to occur via an E1 mechanism. The first step is the rate-determining step, leading to the formation of a tertiary carbocation, followed by base promoted elimination to afford 2 different alkene products. 77
.. :
Br :
H ..
[ - :Br : ] ..
..
HOCH 3 ..
slow H
fast
Topic: Predicting reaction mechanisms Sections: 6.15, 6.16, 6.17 Difficulty Level: Medium
177) When diastereomers I and II undergo an E2 elimination on treatment with sodium ethoxide in ethanol, one of the isomers react 500 times faster than the other on e. Also, one isomer gives only A as a product and the other isomer gives a mixture of A and B as products. Determine the products of each isomer and explain your reasoning.
Ans: By looking at the chair conformations of I and II with the leaving group axial we can see that compound I can only produce B with a hydrogen in anti-perplaner conformation. In addition, this hydrogen has significant steric hindrance caused by the isopropyl group meaning compound I’s reaction will be slow. Compound II lacks this steric hindrance and can give 2 possible products as it has 2 hydrogens that can eliminate anti to the Br.
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Topic: Predicting reaction mechanisms Sections: 6.15, 6.16, 6.17 Difficulty Level: Hard
178) Even though sodium ethoxide is a strong nucleophile and a strong base, only one major product is observed in the reaction below. Explain why.
Ans: Notice that an S N2 reaction is not likely due to sterics of approaching the leaving group Cl from the backside as well as running this reaction in a polar protic solvent. S N1/E1 reaction also seem unlikely as a secondary alk yl halide will not form a very stable carbocation without rearrangement. E2 is the major mechanism dominating the reaction , and to be sensitive to its mechanistic requirements, we must have the Cl le aving group anit-periplaner to the incoming nucleophile.
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