Organic Chemistry I - Exam 2
How many asymmetric carbon atoms are present in the following compound?
0
For the reaction A + B → C + D, ΔG° = -5.00 kcal/mol. What is the corresponding equilibrium constant at 25°C? R = 1.987 cal/mol∙K.
4648
How many asymmetric carbon atoms are present in the following compound?
5
How many asymmetric carbons are present in the compound below?
5
15) Which of the following is a secondary alkyl halide? A) methyl bromide B) isopropyl chloride C) t-butyl iodide D) propyl bromide E) isobutyl chloride
B) isopropyl chloride
Predict the signs of DH° and DS° in the reaction of cyclohexene with H2 to form cyclohexane.
DH° < 0 and DS° < 0
What term describes the structural relationship between (E)- and (Z)-2-pentene?
Diastereomers
75) List the following bromides in order of their increasing reactivity as substrates in SN1 reactions: 2-chlorobutane, 2-iodobutane, and 1-iodobutane.
1-iodobutane < 2-chlorobutane < 2-iodobutane
How many distinct monochlorinated products can result when isobutane is subjected to free radical chlorination?
2
Draw the structure of the diastereomer of (2R,3S)-2,3-dichloropentane. Take the particular care to indicate three-dimensional stereochemical detail properly.
Look at picture
For the structure shown below, draw the stereoisomer having a configuration of (1R,3S,4S) in a perspective structure.
Look at picture
If possible, draw the structure of any diastereomer of the molecule shown below.
Look at picture
If possible, draw the structure of the enantiomer of the molecule shown below.
Look at picture
Label each asymmetric carbon in the compound below as R or S.
Look at picture
Label each asymmetric carbon in the molecule below as having the R or S configuration.
Look at picture
Phantasmidine, shown below, is found in poisonous frog skin and has analgesic properties. Assign each chiral center as having either R or S configuration.
Look at picture
Predict the major monobromination product in the following reaction.
Look at picture
8) Provide an acceptable name for CH3CH2CH2C(CH3)2I.
2-iodo-2-methylpentane
In the hydrocarbon shown below, how many tertiary hydrogens are present?
3
5) Provide the name of the bromoalkane shown below.
3-bromo-4-ethylheptane
Provide the major organic product that results when 2,2,4-trimethylpentane is subjected to free radical bromination.
Look at picture
Provide the major organic product(s) in the reaction below
Look at picture
Provide the major organic product(s) in the reaction below.
Look at picture
Provide the structure of the carbene that results when diazomethane (shown below) decomposes.
Look at picture
Provide the structure of the transition state in the first propagation step of the free radical chlorination of ethane.
Look at picture
Provided the following pKa values for the two acids below, draw an energy diagram for the acid-base reaction. Be sure to label each axis correctly.
Look at picture
Remove an H+ from the following structure to create the most reactive (least stable) carbanion
Look at picture
Translate the structure below to a Fischer projection.
Look at picture
When compound I, C7H16, was treated with chlorine and light it yielded 3 monochlorination products that could be separated by chromatography. Two of the products were primary alkyl halides and the other was a secondary alkyl halide. Provide a possible structure for compound I.
Look at picture
Which of the following depictions most closely resembles the structure of the transition state for the following acid-base reaction?
Look at picture
Can the molecule shown below be properly described as a meso compound? (CH3)2CHCH2CH3
No
Given that the theoretical reaction below was found to be second order and bimolecular, provide a rate equation for the reaction. A-B + C-D → A-C + B-D
Rate = kr[AB][CD]
In the reaction of Cl2 with ethane and UV light, which of the following reactions would be a propagation event(s)?
Reactions II and IV
The process by which enantiomers are separated is called _________.
Resolution
What reactive intermediate is formed when CHBr3 is treated with hydroxide or when diazomethane is irradiated?
carbene
45) Name one factor that is favorable for nucleophilicity but not for basicity.
polarizability
When 1,1,3,3-tetramethylcyclobutane is brominated at 125°C, the relative reactivity of the 1°: 2°:3° hydrogens is approximately 1:82:1600. Estimate the amount of each monobromination product.
primary bromide, 3.5%; secondary bromide, 96.5%
24) The term CFC is an abbreviation for ________.
chlorofluorocarbon
7) Provide an acceptable name for CHCl3.
chloroform
Energy is ________ when bonds are formed and is ________ when bonds are broken; therefore, bond dissociation energies are always ________.
released / consumed / endothermic
82) If the absolute configuration at an asymmetric carbon does not change during the course of a reaction, the reaction is said to occur with ________ of stereochemistry.
retention
What is the CCC bond angle in (CH3)3C:-?
slightly less than 109.5 degrees
What is the hybridization of the positively charged carbon in (CH3)3C+?
sp2
What is the hybridization of the negatively charged carbon in (CH3)3C:-?
sp3
Given the bond dissociation energies below (in kcal/mol), calculate the overall ΔH° for the following reaction: (CH3)3CH + Br2 → (CH3)3CBr + HBr (CH3)3CH 91 (CH3)3CBr 65 BrBr 46 HBr 88 CH3Br 70
-16 kcal/mol
How many asymmetric carbon atoms are present in the following compound?
1
How many asymmetric carbons are present in the compounds below? 3-ethyl-2,2,4-trimethylpentane
1
110) Provide a series of synthetic steps by which (CH3)2C CH2 could be prepared from 2-methylpropane.
1) Br2, hν 2) NaOCH3, CH3OH
How many asymmetric carbon atoms are present in the following compound?
2
How many asymmetric carbons are present in the compounds below?
2
How many diastereomers are there of the molecule shown below?
2
Given a DG° of 0.8 kJ/mol at 25°C for the equilibrium shown below, calculate the percentage of the axial conformer at 25°C. [R = 8.314 J/K∙ mol]
42%
72) Which of the following alkyl bromides undergoes solvolysis in aqueous methanol most rapidly? A) PhCHBrCH3 B) (CH3)2CHCH2CH2Br C) (CH3)2CHCH2CHBrCH3 D) CH3CH2CH2CH2Br E) PhBr
A) PhCHBrCH3
Is the molecule shown below chiral or achiral?
Achiral
Is the molecule shown below chiral or achiral? (CH3)3CCH(CH3)2
Achiral
78) List the following compounds in order of increasing reactivity in an SN1 reaction. CH3Br, CH3CH2CH2I, (CH3)3CI, CH3CHBrCH3, CH3CHICH3
CH3Br < CH3CH2CH2I < CH3CHBrCH3 < CH3CHICH3 < (CH3)3CI
20) Provide the structure of 1-bromo-3-methylhexane.
CH3CH2CH2CH(CH3)CH2CH2Br
Provide the two propagation steps in the free-radical chlorination of ethane
CH3CH3 + Cl∙ → CH3CH2∙ + HCl CH3CH2∙ + ClCl → CH3CH2Cl + Cl∙
The relationship between I and III is: _____________.
Diastereomers
123) Which of the following mechanisms (SN1, SN2, E1, E2) feature(s) a carbocation intermediate? A) SN1 only B) SN2 only C) E1 only D) E2 only E) both SN1 and E1
E) both SN1 and E1
16) Which of the following is a primary alkyl halide? A) methyl bromide B) isopropyl bromide C) t-butyl iodide D) cyclohexyl bromide E) isobutyl chloride
E) isobutyl chloride
Which of the following species is not formed through a termination reaction in the chlorination of methane?
H2
Explain the significance of the exponential factor e-Ea/RT in the Arrhenius equation
The exponential factor e-Ea/RT in the Arrhenius equation corresponds to the fraction of collisions in which the reacting molecules have the appropriate activation energy to react at a given temperature.
If possible, draw the enantiomer of the molecule shown below.
The molecule is an achiral. It does not have an enantiomer.
The major monobrominated product which results when ethylcyclohexane is subjected to free radical bromination is:
a tertiary bromide.
64) SN2 reactions take place with ________ of stereochemistry at the center undergoing substitution.
inversion
The difference in energy between reactants and the transition state is known as ________
the activation energy or Ea
What term describes the highest-energy structure in a molecular collision which leads to reaction?
transition state
Which of the following correctly expresses the standard Gibbs free energy change of a reaction in terms of the reaction temperature (T) and equilibrium constant (K)?
ΔG° = -RTlnK
22) Name the haloalkane shown. Be sure to include the appropriate R or S description if needed.
(3R,4R,6S)-4-ethyl-1,6-difluoro-3-methylheptane
Which of the following configurations corresponds to the structure below?
(4R,5R)
Of the two C-H bonds shown, which has the smaller bond dissociation energy? Explain your choice. (CH3)2CH-H vs. CH3CH2-H
(CH3)2CH-H has the smaller bond dissociation energy. This homolytic bond cleavage yields a more stable secondary radical.
10) Provide the structure of isopropyl iodide.
(CH3)2CHIf
Predict the major monobromination product in the following reaction.
(CH3)3CCHBrCH3
46) Arrange the following species in order of increasing nucleophilicity:
(CH3)3COH < (CH3)3CO- < CH3CH2O- < CH3CH2S-
What C5H12 isomer will give only a single monochlorination product?
(CH3)4C or neopentane or 2,2-dimethylpropane
23) Name the haloalkane shown. Be sure to include the appropriate R or S description if needed.4
(S)- 3-chloro-1,1-dimethylcyclohexane
A newly isolated natural product was shown to be optically active. If a solution of 2.0 g in 10 mL of ethanol in a 50 cm tube gives a rotation of +2.57º, what is the specific rotation of this natural product?
+2.57º
A mixture of two enantiomers with a composition of 65.0% R has an observed rotation of -25.3º in a 10.0 cm polarimeter tube. If the mixture has a concentration of 2.038 g/mL at 25ºC, what is the predicted [a]25D of an optically pure sample of the S enantiomer?
+41.3º
Consider the three-step mechanism for the reaction of A through intermediates B and C to produce D shown below A → B Ea = 15 kcal/mol, ΔH° = 13 kcal/mol B → C Ea = 10 kcal/mol, ΔH° = -6 kcal/mol C → D Ea = 2 kcal/mol, ΔH° = -20 kcal/mol What's the enthalpy difference between reactant A and intermediate C?
+7 kcal/mol
Predict the enthalpy (ΔH) value for the theoretical reaction below, and indicate whether it is endothermic or exothermic. The bond dissociation energy for each bond in Kcal/mol is shown below each reactant and product. A-B + C-D → A-C + B-D 63 88 47 96
+8 Kcal/mol, endothermic
If (S)-glyceraldehyde has a specific rotation of -8.7º, what is the specific rotation of (R)-glyceraldehyde?
+8.7º
Consider the transformation of A to B (i.e., A → B). If at equilibrium at 25°C the concentration of A is 20% of the initial concentration of A, determine the value of ΔG° (in kcal/mol) for this reaction. R = 1.987 cal/mol∙K.
-0.82 kcal/mol
(-)-lactic acid has a specific rotation of -3.8º. What is the specific rotation of a solution containing 7.5 g of (-)-lactic acid and 2.5 g of (+)-lactic acid?
-1.9º
A student measured the optical activity of an unknown sugar at two different concentrations. The results of his measurements are shown below. Given that the sample cell had a path length of 10.0 cm, calculate the specific rotation for the unknown sugar. (Hint: Consider each measurement of plane polarized light has a true reading and a "ghost" reading 180º from the true reading).
-105º
Given a K of 2.2 at 25°C, calculate the corresponding DG° in kJ/mol. [R = 8.314 J/K∙ mol]
-2.0 kJ/mol
Given the bond dissociation energies below (in kcal/mol), estimate the ΔH° for the propagation step CH3)2CH∙ + C12 → (CH3)2CHCl + Cl∙ CH3CH2CH2H 98 (CH3)2CHH 95 ClCl 58 HCl 103 CH3CH2CH2Cl 81 (CH3)2CHCl 80
-22 kcal/mol
Consider the conversion of C to D via a one-step mechanism. The activation energy of this conversion is 3 kcal/mol. The energy difference between D and the transition state of the reaction is 7 kcal/mol. Estimate ΔH° for the reaction C → D
-4 kcal/mol
How many enantiomers are there of the molecule shown below?
0
For a given reaction, if ΔG° is greater than zero, then:
0 < Keq < 1
Consider the reaction of A being converted into B at 25°C. If the ΔG° of this reaction is +1.0 kcal/mol, the Keq is ________ and the % conversion is ________.
0.18, 15%
Given that glucose has a specific rotation of +52.8º. Predict the concentration of a glucose aqueous solution contained in a 10 cm long polarimetry tube if a rotation of +15.8º was observed.
0.299 g/mL
Consider the reaction of A being converted into B at 25°C. If the ΔG° of this reaction is +0.5 kcal/mol, the Keq is ________ and the % conversion is ________
0.43, 30%
Assume the reaction A + B → C + D proceeds to equilibrium. Calculate the equilibrium concentration of D at 25°C, given that the starting concentrations of A and B are 2M and that ΔG° for the reaction is 1.0 kcal/mol. R = 1.987 cal/mol∙K.
0.60M
How many distinct monochlorinated products can result when cyclopentane is subjected to free radical chlorination?
1
How many enantiomers are there of the molecule shown below?
1
Which of the following structures are achiral and meso?
1 & 4
What is the name of the major monobrominated product which results when methylcyclohexane is subjected to Br2/hν conditions?
1-bromo-1-methylcyclohexane
Given that tertiary H atoms react with a chlorine radical about 5.5 times faster than primary ones, estimate the ratio of the two monochlorinated products that result when 2,3-dimethylbutane undergoes free radical chlorination
1-chloro-2,3-dimethylbutane, 52%; 2-chloro-2,3-dimethylbutane, 48%
E) 5
101) How many distinct alkene products are possible, including stereoisomers, when the alkyl iodide below undergoes E2 elimination? A) 1 B) 2 C) 3 D) 4 E) 5
What is the CCC bond angle in (CH3)3C+?
120 degrees
137) A) SN1
137) Consider the substitution reaction shown below. By what mechanism will the reaction proceed? A) SN1 B) SN2 C) Free radical reaction D) There is not enough information to tell.
138) B) SN2
138) Consider the substitution reaction shown below. By what mechanism will the reaction proceed? A) SN1 B) SN2 C) Free radical reaction D) There is not enough information to tell. Answer: B Diff: 2 Section: 6.16 LO: 6.7
55) Arrange the following substrates in order of their increasing SN2 reactivity with NaCN: bromoethane, 1-chloro-3,3-dimethylpentane, 1-chloro-2,2-dimethylpentane, and 2-bromo-2-methylpentane.
2-bromo-2-methylpentane < 1-chloro-2,2-dimethylpentane < 1-chloro-3,3-dimethylpentane < bromoethane
57) List the following alkyl halides in order of their increasing reactivity as substrates in SN2 reactions: 2-chlorobutane, 2-iodobutane, and 1-iodobutane.
2-chlorobutane < 2-iodobutane < 1-iodobutane
Given a K of 0.45 at 25°C, calculate the corresponding DG° in kJ/mol. [R = 8.314 J/K∙ mol]
2.0 kJ/mol
Consider the reaction of A being converted into B at 25°C. If the ΔG° of this reaction is -0.5 kcal/mol, the Keq is ________ and the % conversion is ________.
2.3, 70%
Given a DG° of -8.0 kJ/mol at 25°C, calculate the corresponding K. [R = 8.314 J/K∙ mol]
25
29) Arrange the following alkyl halides in order of increasing boiling point: CH3CH2Br, CH3CH2CH2Br, (CH3)2CHBr, CH3CH2F.
29) Arrange the following alkyl halides in order of increasing boiling point: CH3CH2Br, CH3CH2CH2Br, (CH3)2CHBr, CH3CH2F.
How many distinct dichlorination products can result when isobutane is subjected to free radical chlorination?
3
What is the name of the major monobrominated product which results when 3-methylpentane is subjected to Br2/hν conditions?
3-bromo-3-methylpentane
Given a reaction in which reactant A is converted only to product B at 25°C, what Keq results if at equilibrium 80% of A has become B?
4
19) Provide an acceptable name for the compound shown below.
4-bromo-1,1 dimethylcyclohexane
A certain free radical chlorination reaction of 2,3-dimethylbutane leads to the production of two major monochlorinated products 1-chloro-2,3-dimethylbutane and 2-chloro-2,3-dimethylbutane. When run through a Gas chromatograph, it was determined that the product distribution was 51.7% 1-chloro-2,3-dimethylbutane and 48.3% 2-chloro-2,3-dimethylbutane. If we assign the primary H's a reactivity of 1.0, what is the relative reactivity of the tertiary H's?
5.6 times more reactive
If a mixture contains 75% of one compound and 25% of its enantiomer, what is the e.e. of the mixture?
50
How many diastereomers are there of the molecule shown below?
6
How many secondary hydrogens are present in the hydrocarbon below?
6
Calculate the e.e. of a mixture containing 8.0 g of (-)-glyceraldehyde and 2.0 g of (+)-glyceraldehyde.
60%
One of the stereoisomers of the following oblongolide structure is a natural product isolated from a fungus and has been found to contain antiviral cytotoxic activities. How many stereoisomers exist for this structure?
64
The specific rotation of pure (-)-2-butanol is -13.5º. What % of a mixture of the two enantiomeric forms is the (+)-form if the specific rotation of this mixture is +7.0º?
76%
B) 2 < 3 < 4 < 1 < 5
80) Rank the following molecules in order of increasing relative rate of SN1 solvolysis with methanol and heat (slowest to fastest reacting). A) 3 < 2 < 4 < 5 < 1 B) 2 < 3 < 4 < 1 < 5 C) 5 < 4 < 3 < 2 < 1 D) 2 < 3 < 4 < 5 < 1 E) 1 < 2 < 5 < 4 < 3
A) Net inversion 25% with 75% racemization — SN1 mechanism
91) A sample of 1-chloro-1-phenylethane with an [α]25D of -94.8° is reacted with NH3 in methanol/water solvent. The major substitution product of the reaction is 1-phenyl-1-ethylamine with an [α]25D of -8.6°. Given that optically pure (R) 1-chloro-1-phenylethane has a specific rotation of -109.0° and that optically pure (R) 1-phenyl-1-ethylamine has a specific rotation of +39.3°, which of the following statements best describes this reaction? A) Net inversion 25% with 75% racemization — SN1 mechanism B) Net inversion 12% with 88% racemization — SN1 mechanism C) Net inversion 75% with 25% racemization — SN2 mechanism D) Net inversion 12% with 88% racemization — SN2 mechanism E) Net inversion 88% with 12% racemization — SN2 mechanism
Which of the following is a carbene?
:CCl2
In the first propagation step of the free radical chlorination of methane, which of the following occurs?
A chlorine radical abstracts a hydrogen.
54) Which of the following alkyl chlorides will undergo SN2 reaction most readily? A) 1-chloro-4-methylpentane B) 2-chloro-4-methylpentane C) 2-chloro-3-methylpentane D) 3-chloro-2-methylpentane E) 2-chloro-2-methylpentane
A) 1-chloro-4-methylpentane
63) Which of the following alkyl halides reacts most rapidly via an SN2 reaction with NaCN? A) 1-iodohexane B) 1-fluorohexane C) (R)-2-bromohexane D) iodocyclohexane E) 1-iodo-1-methylcyclohexane
A) 1-iodohexane
31) When 2,2-dimethylbutane is subjected to free-radical chlorination, ________ distinct monochlorinated products are possible and ________ of these contain asymmetric carbon atoms A) 4; 2 B) 5; 0 C) 3; 0 D) 5; 2 E) 4; 0
A) 4; 2
44) Which of the following compounds is the most nucleophilic? A) CH3SH B) CH3OH C) H2O D) CH3CO2H E) BF3
A) CH3SH
125) Predict the most likely mechanism for the reaction shown below. you A) SN1 B) SN2 C) E1 D) E2 E) E1cb
A) SN1
130) One product which results when 2-chloro-2-methylpentane is heated in ethanol is an ether. From which mechanistic pathway does this ether arise? A) SN1 B) SN2 C) E1 D) E2 E) E1cb
A) SN1
62) Which of the following statements describe a favorable attribute of a leaving group? (More than one answer is possible.) A) The leaving group should be highly polarizable. B) The lower the electronegativity of the leaving group the better. C) Good leaving groups need to have low steric hindrance. D) The departed leaving group should have low basicity.
A) The leaving group should be highly polarizable. D) The departed leaving group should have low basicity.`
14) Which of the following is a vicinal dihalide? A) cis-1,2-dibromocyclopentane B) 3,3-dichloropentane C) trans-1,4-diiodocyclohexane D) isobutyl chloride E) 1,3-dibromoheptane
A) cis-1,2-dibromocyclopentane
51) Which of the following solvents could be described as polar and protic? A) ethanol B) acetonitrile C) dimethylformamide D) acetone E) 18-crown-6
A) ethanol
132) When 3-iodo-3-ethylpentane is heated in methanol, the major organic product is an ________ that is generated through an ________ mechanism. A) ether; SN1 B) ether; SN2 C) ether; E1 D) alkene; E2 E) alcohol; E1 Answer: A
A) ether; SN1
50) Which of the following factors is favorable for nucleophilicity but not basicity? A) highly polarizable B) low electronegativity C) negatively charged D) sterically hindered
A) highly polarizable
28) Among the following alkyl halides, choose the one with the lowest boiling point. A) t-butyl chloride B) n-butyl chloride C) t-butyl bromide D) n-butyl iodide E) t-butyl iodide
A) t-butyl chloride
Is the molecule shown below chiral or achiral? CH3CH2CH(CH3)CH2CH3
Achiral
18) What is the IUPAC name of the compound shown below? A) (2R,3S,4S)-2-chloro-3,4-dibromo-3-methylhexane B) (2R,3S,4S)-3,4-dibromo-2-chloro-3-methylhexane C) (3S,4S,5S)-3,4-dibromo-5-chloro-4-methylhexane D) (2R,3R,4S)-3,4-dibromo-2-chloro-3-methylhexane E) (2R,3S,4R)-3,4-dibromo-2-chloro-3-methylhexane
B) (2R,3S,4S)-3,4-dibromo-2-chloro-3-methylhexane
103) How many distinct alkene products results when 1-bromo-1-ethylcyclopentane is treated with NaOCH3? A) 1 B) 2 C) 3 D) 4
B) 2
89) Which of the following alkyl halides is most likely to undergo rearrangement in an SN1 reaction? A) 3-bromopentane B) 2-chloro-3,3-dimethylpentane C) 3-chloropentane D) bromocyclohexane E) 1-bromo-4-methylcyclohexane
B) 2-chloro-3,3-dimethylpentane
88) Which of the cations below would be subject to a structural rearrangement? A) 1 B) 3 C) 1, 2, & 3 D) 2 & 3
B) 3
13) Which of the following is a geminal dihalide? A) cis-1,2-dibromocyclopentane B) 3,3-dichloropentane C) trans-1,4-diiodocyclohexane D) isobutyl chloride E) 1,3-dibromoheptane
B) 3,3-dichloropentane
102) Which of the following alkyl halides can produce only a single alkene product from when treated with sodium methoxide? A) 2-chloro-2-methylpentane B) 3-chloro-3-ethylpentane C) 3-chloro-2-methylpentane D) 2-chloro-4-methylpentane E) 2-chloro-3-ethylpentane
B) 3-chloro-3-ethylpentane
43) Which of the following species is the least nucleophilic? A) H2O B) BF3 C) (CH3)3N D) CH3O- E) CN-
B) BF3
2) Which of the following is classified as a vinylic halide? A) CH3CH=CHOH B) CH3CH=CHCl C) CH3CH=CHCH2Cl D) CH3CH2CH2CH2Br E) BrCH2CH=CH2
B) CH3CH=CHCl
41) Consider the substitution reaction shown below. By what mechanism will the reaction proceed? A) SN1 B) SN2 C) free radical reaction D) There is not enough information to tell
B) SN2
84) When trans-1-iodo-4-methylcyclohexane is heated in methanol, the product mixture is primarily ________. A) a single, chiral compound B) a mixture of diasteromeric ethers C) a mixture of diasteromeric alcohols D) a single, chiral alcohol E) a single, chiral ether
B) a mixture of diasteromeric ethers
1) Which of the following best describes the carbon-chlorine bond of an alkyl chloride? A) nonpolar; no dipole B) polar; δ+ at carbon and δ- at chlorine C) polar; δ- at carbon and δ+ at chlorine D) ionic E) none of the above
B) polar; δ+ at carbon and δ- at chlorine
86) SN1 reactions usually proceed with ________. A) equal amounts of inversion and retention at the center undergoing substitution B) slightly more inversion than retention at the center undergoing substitution C) slightly more retention then inversion at the center undergoing substitution D) complete inversion at the center undergoing substitution E) complete retention at the center undergoing substitution
B) slightly more inversion than retention at the center undergoing substitution
21) The following structure is a proteasome inhibitor that may find application in treating cervical cancer (J. Med. Chem. 2011, 449). The halides in this structure may be classified as ________ and ________. A) vicinal; vinyl B) vicinal; aryl C) vinyl; aryl D) vinyl; geminal
B) vicinal; aryl
Within the visible spectrum, it has been experimentally determined that blue light is the most effective in initiating the chlorination of methane. What is the mechanistic significance of this observation?
Blue light is effectively absorbed by chlorine but not by methane. Thus the initiating step is most likely the production of two chlorine atoms from molecular chlorine.
Which of the following molecules, if isolated in its pure form, would demonstrate optical activity?
Both IV and V
12) Which of the following is a tertiary halide? A) ClCH2CH2C(CH3)3 B) ClCH2CH2CH(CH3)2 C) (CH3)2CClCH2CH3 D) (CH3)3CCHClCH3 E) ClCH2C(CH3)CH2CH3
C) (CH3)2CClCH2CH3
90) Which of the following alkyl chlorides is least likely to undergo rearrangement during a solvolysis reaction? A) 2-chloro-4-methylpentane B) 2-chloro-3-methylpentane C) 2-chloro-2-methylpentane D) cis-1-chloro-2-ethylcyclohexane E) trans-1-chloro-2-ethylcyclohexane
C) 2-chloro-2-methylpentane
136) Rank the following compounds in order of increasing reactivity in an SN2 reaction. (Fastest is first, slowest is last.) A) III > I > II > IV B) II > IV > I > III C) IV > II > I > III D) IV > II > III > I
C) IV > II > I > III
127) Predict the two most likely mechanisms for the reaction of 2-iodohexane with potassium hydroxide. A) SN1 and SN2 B) E1 and E2 C) SN2 and E2 D) E1 and SN1
C) SN2 and E2
100) Dehydration of 1-butanol with concentrated sulfuric acid at 140∘C results in the formation of mainly trans-2-butene. According to these results, which of the following conclusions might be valid? A) The reaction undergoes an E2-type elimination mechanism. B) The reaction follows a new mechanism involving the formation of a carbanion intermediate. C) The reaction undergoes an E1-type elimination mechanism in conjunction with a hydride shift. D) The reaction undergoes an E2-type elimination mechanism in conjunction with a methyl shift. E) The reaction undergoes an E1-type elimination mechanism with no shifting.
C) The reaction undergoes an E1-type elimination mechanism in conjunction with a hydride shift.
83) When a SN1 reaction of R-2-iodobutane takes place in hot methanol, the product ________. A) is chiral B) will rotate plane polarized light C) is racemic D) will undergo a hydride shift E) none of the above
C) is racemic
118) When (cis)-1-bromo-2 methylcyclohexane is treated with methanol and heat, four different products are formed — two by substitution and two by elimination. Which of the following conditions would change the outcome of this reaction by promoting the production of 3-methylhexene as the major product? A) KOH, ethanol and heat B) water/acetone and heat C) tert-butoxide/tert-butyl alcohol D) tert-butyl alcohol and heat E) methoxide/methanol
C) tert-butoxide/tert-butyl alcohol
4) What general classification is given to the molecule below? A) primary chloride B) secondary chloride C) tertiary chloride D) vinyl chloride E) benzyl chloride
C) tertiary chloride
3) The flame retardant below has been found to be an androgen agonist and may have a contribution to an increasing rate of occurrence of prostate cancer (J. Med. Chem. 2006, 7366). What is the correct term that describes the relative position of the bromides in this structure? A) geminal B) vinyl C) vicinal D) aryl
C) vicinal
When light is shined on a mixture of chlorine and chloromethane, carbon tetrachloride is one of the components of the final reaction mixture. Propose a series of mechanistic steps which explain this observation.
CH3Cl + Cl∙ → ∙ CH2Cl + HCl ∙CH2Cl + Cl-Cl → CH2Cl2 + Cl∙ CH2Cl2 + Cl∙ → ∙ CHCl2 + HCl ∙CHCl2 + Cl-Cl → CHCl3 + Cl∙ CHCl3 + Cl∙ → ∙ CCl3 + HCl ∙CCl3 + Cl-Cl → CCl4 + Cl
When Br radical reacts with 1-butene (CH3CH2CH=CH2), the hydrogen atom which is preferentially abstracted is the one which produces a resonance stabilized radical. Draw the major resonance contributing forms of this radical.
CH3HCHCH2 ↔ CH3CHCH H2
61) Show the best way to prepare CH3OCH(CH3)2 by an SN2 reaction.
CH3I + NaOCH(CH3)2
List the following radicals in order of increasing stability (i.e., from least stable to most stable) (CH3)3C∙, CH2CHCH2∙, CH3CH2∙, CH3∙, (CH3)2CH∙
CH3∙ < CH3CH2∙ < (CH3)2CH∙ < (CH3)3C∙ < CH2CHCH2∙
Describe the hybridization of the cationic center and predict the CCC bond angle in (CH3)3C+
Cationic center is sp2 hybridized, therefore the CCC bond angle is 120°.
Is the molecule shown below chiral or achiral?
Chiral
87) Provide two circumstances under which solvolysis of a chiral alkyl halide would not result in the generation of a mixture of enantiomeric products.
Choose two from among: (i) leaving group not bound to stereocenter (ii) rearrangement yields a carbocation in which two groups bound to the cationic center are the same (iii) the molecule contains at least one additional stereocenter which is unaffected by the ionization (iv) rearrangement ultimately results in a meso compound Diff: 3
Write an equation to describe the initiation step in the chlorination of methane.
Cl-Cl + photon (hν) → 2 Cl∙
The relative reactivity of the 1°: 2°: 3° hydrogens of (CH3)3CCH2CH3 in free radical chlorination is 1: 3.8: 5.0. Provide the structure of each monochlorination product, and estimate the relative amount of each in the mixture of monochlorinated products.
ClCH2C(CH3)2CH2CH3, 45.9%; (CH3)3CCHClCH3, 38.8%; (CH3)3CCH2CH2Cl, 15.3%
What is the structural relationship between the two molecule shown below?
Constitutional Isomers
What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,5R)-2,3,5-trichloroheptane?
Constitutional Isomers
What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,3-dimethylcyclopentane?
Constitutional Isomers
17) What is the IUPAC name of the compound shown below? A) (1S,3S)-1,3-dichloro-1-ethyl-3-methylcyclopentane B) (1R,3S)-1,3-dichloro-1-methyl-3-ethylcyclopentane C) (1R,4S)-1,4-dichloro-1-ethyl-4-methylcyclopentane D) (1R,3S)-1,3-dichloro-1-ethyl-3-methylcyclopentane E) (1S,3R)-1,3-dichloro-3-ethyl-1-methylcyclopentane
D) (1R,3S)-1,3-dichloro-1-ethyl-3-methylcyclopentane
11) Which of the following is a secondary halide? A) ClCH2CH2C(CH3)3 B) ClCH2CH2CH(CH3)2 C) (CH3)2CClCH2CH3 D) (CH3)3CCHClCH3 E) ClCH2C(CH3)CH2CH3
D) (CH3)3CCHClCH3
128) Predict the two most likely mechanisms that occur when iodocyclohexane is heated in methanol. A) SN1 and SN2 B) E1 and E2 C) SN2 and E2 D) E1 and SN1
D) E1 and SN1
126) Predict the most likely mechanism for the reaction shown below. A) SN1 B) SN2 C) E1 D) E2 E) E1cb
D) E2
129) The major product from the reaction of 2-chloro-2-methylpentane with sodium ethoxide in ethanol results from which of the following mechanistic pathways? A) SN1 B) SN2 C) E1 D) E2 E) Ecb
D) E2
131) When 3-iodo-3-ethylpentane is treated with sodium methoxide in methanol, the major organic product is an ________ that is generated through an ________ mechanism. A) ether; SN1 B) ether; SN2 C) ether; E1 D) alkene; E2 E) alkene; E1
D) alkene; E2
Predict the sign of DS° in the combustion of propane.
DS°>0
Compounds that rotate the plane of polarized light clockwise are called _________.
Dextrorotatory
The relationship between I and II is: ______________.
Diastereomers
What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2R,3R,4R)-2,3,4-trichloroheptane?
Diastereomers
What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,2-dimethylcyclopentane?
Diastereomers
Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?
Diastereomers
Which of the following terms correctly describe(s) the structural relationship between cis-1,3-dimethylcyclopentane and trans-1,3-dimethylcyclopentane?
Diastereomers & geometric isomers
53) Which of the following compounds will undergo an SN2 reaction most readily? A) (CH3)3CCH2I B) (CH3)3CCl C) (CH3)2CHI D) (CH3)2CHCH2CH2CH2I E) (CH3)2CHCH2CH2CH2Cl
E) (CH3)2CHCH2CH2CH2Cl
79) Which of the following alkyl halides reacts most rapidly via an SN1 solvolysis reaction in hot methanol? A) 1-iodohexane B) 1-fluorohexane C) (R)-2-bromohexane D) iodocyclohexane E) 1-iodo-1-methylcyclohexane
E) 1-iodo-1-methylcyclohexane
71) Which of the compounds below undergoes solvolysis in aqueous ethanol most rapidly? A) cyclohexyl bromide B) methyl iodide C) isopropyl chloride D) 3-chloropentane E) 3-iodo-3-methylpentane
E) 3-iodo-3-methylpentane
26) Which of the following alkyl halides has the smallest molecular dipole moment? A) CH3F B) CH3Cl C) CH2I2 D) CH2Cl2 E) CF4
E) CF4
133) Which of the following carbocations is likely to undergo a hydride shift? A) I B) II C) III D) IV E) II and IV F) II and III
E) II and IV
95) Which of the following statements correctly describe(s) E1 reactions of alkyl halides (RX)? I. Rate = k[base] II. Rate = k[base][RX] III. Rate = k[RX] IV. The reactions occur in two or more distinct steps. V. Rearrangements are sometimes seen. A) II and IV B) III and V C) I, IV, and V D) I only E) III, IV, and V
E) III, IV, and V
38) What type of intermediate is present in the SN2 reaction of cyanide with bromoethane? A) carbocation B) free radical C) carbene D) carbanion E) This reaction has no intermediate.
E) This reaction has no intermediate.
25) Which of the following best describes DDT? A) a chlorocarbon used to decaffeinate coffee beans B) a polybrominated organic compound used as a herbicide C) a Freon used as a foaming agent D) a mixed alkyl halide used as an anesthetic E) a polychlorinated organic compound used as an insecticide
E) a polychlorinated organic compound used as an insecticide
124) In which of the following mechanisms (SN1, SN2, E1, E2) are alkenes the major reaction products? A) SN1 only B) SN2 only C) E1 only D) E2 only E) both E1 and E2
E) both E1 and E2
What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,4R)-2,3,4-trichloroheptane?
Enantiomers
Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?
Enantiomers
Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?
Enantiomers has
48) Which is more nucleophilic, t-butoxide or ethoxide? Explain.
Ethoxide is the better nucleophile. The steric bulk of t-butoxide decreases its effectiveness as a nucleophile.
If stronger bonds are formed and weaker bonds are broken, then the reaction is ________.
Exothermic
32) Draw two reasonable resonance structures and the hybrid of the intermediate formed in the following reaction.
Free Radical mechanism at the allylic C's
If the equilibrium constant (Keq) of a reaction is 0.5 then which of the following that must be true?
Gibbs free energy (G) is positive.
49) Rank the species below in order of increasing nucleophilicity in hydroxylic solvents: CH3CO2-, CH3S-, HO-, H2O.
H2O < CH3CO2- < HO- < CH3S-
In an exothermic reaction, are stronger bonds broken and weaker bonds formed or are weaker bonds broken and stronger bonds formed?
In an exothermic reaction, weaker bonds are broken and stronger bonds are formed
99) What is Zaitsev's rule?
In elimination reactions, the most highly substituted alkene product is the major product.
Explain how the termination step in a free-radical chain reaction stops the chain
In order for a free-radical chain to propagate, each mechanistic step must yield a free-radical species as one of its products. A mechanistic step that does not yield a free-radical stops the chain. Such a step is known as a termination step
Free radical bromination of pentane results in poor yields of 1-bromopentane, while cyclopentane can be readily brominated under similar conditions to yield bromocyclopentane. Offer an explanation.
In the bromination of pentane, the lowest energy reaction pathways go through secondary free radical intermediates to produce secondary alkyl bromides (2-bromopentane and 3-bromopentane). Thus 1-bromopentane is a very minor product. All of the hydrogen atom abstractions of cyclopentane lead to the same secondary radical which eventually leads to bromocyclopentane.
The Arrhenius equation mathematically models which of the following statements?
Increasing the temperature of a chemical reaction increases the number of particles in the reaction that have the minimum energy required to meet the Ea. & The rate of a chemical reaction is exponentially related to the Ea and relatively small differences in the Ea can dramatically affect the reaction rates of similar reactions at the same temperature.
A mixture of equal amounts of two enantiomers __________.
Is called a racemic mixture & is optically inactive
If ΔG° for a given reaction at 25°C is less than zero, which of the following statements also correctly describes this reaction at this temperature?
Keq is greater than zero.
Consider the one-step conversion of F to G. Given that the reaction is endothermic by 5 kcal/mol and that the energy difference between G and the transition state for the process is 15 kcal/mol, sketch a reaction-energy diagram for this reaction. Make sure to show how the given energy differences are consistent with your sketch.
Look at picture
Consider the reaction: CH3CH2∙ + Br2 → CH3CH2Br + Br∙ Given that this reaction has an activation energy of +6 kcal/mol and a ΔH° of -22 kcal/mol, sketch a reaction-energy diagram for this reaction. Label the axes and show Ea and ΔH° on your drawing
Look at picture
Draw all monochlorination products expected from reaction of chlorine with 3,4-dimethylhexane. Circle the major product
Look at picture
Draw an energy diagram for a two step reaction where the structure of the transition state of the rate determining step most closely resembles the starting material and the overall reaction is exothermic.
Look at picture
Draw any diastereomer of the molecule shown below.
Look at picture
Draw the Fischer projection of (2R,4R)-2,4-dibromopentane.
Look at picture
Draw the Fischer projection of (S)-2-bromobutane.
Look at picture
Draw the Fischer projection of (S)-2-hydroxybutanoic acid, CH3CH2CH(OH)COOH.
Look at picture
Draw the enantiomer of the molecule shown below.
Look at picture
Draw the structure of (1R,2R)-1-bromo-2-chlorocyclobutane. Take particular care to indicate stereochemistry properly.
Look at picture
Draw the structure of (1R,2S,3S)-1,2-dibromo-3-ethylcyclohexane. Take particular care to indicate stereochemistry properly.
Look at picture
Draw the structure of (2R,3R)-2,3-dibromo-3-chloropentane.
Look at picture
Draw the structure of (2R,3S)-2,3-dichloropentane. Take the particular care to indicate three-dimensional stereochemical detail properly.
Look at picture
Draw the structure of (S)-1-bromo-1-chloropropane. Take the particular care to indicate three-dimensional stereochemical detail properly.
Look at picture
Draw the structure of (S)-3-chloro-3-methylhexane. Take particular care to indicate stereochemistry properly.
Look at picture
Draw the structure of the enantiomer of (2R,3S)-2,3-dichloropentane. Take the particular care to indicate three-dimensional stereochemical detail properly.
Look at picture
Draw the structure of the meso form of 1,3-dichlorocyclopentane. Take particular care to indicate three-dimensional stereochemical detail properly.
Look at picture
Provide a Fischer projection of (2R,3R,4S)-2,3,4-trichloroheptane.
Look at picture
Provide a Fischer projection of (2S,3S,4S)-2,3,4-trichloroheptane.
Look at picture
When acetaldehyde (CH3CHO) is deprotonated, the resulting anion is stabilized by resonance. Draw the major resonance contributing forms of this anion
Look at picture
Which of the presented mechanisms would be the most energetically favorable and thus the most likely mechanism to actually occur for the following free radical chain reaction? (bond dissociation energies -- H-H = 104 kcal/mol; Cl-Cl = 58 kcal/mol; H-Cl = 103 kcal/mol)
Look at picture
Write a detailed, stepwise mechanism for the following reaction.
Look at picture
Write the structures of all of the monobromination products of 1,1,3,3-tetramethylcyclobutane
Look at picture
Chlorination of methane can result in a mixture of chlorinated products. What experimental conditions should be used to favor the production of chloromethane over the other chlorinated products?
Make sure the molar ratio of methane to chlorine is relatively large. Additionally, lower reaction temperature also helps prevent multiple chlorination.
The chlorination of methane is characterized by a high quantum yield. Explain what this means.
Many molecules of product are formed for every photon of light which is absorbed by the reaction mixture.
Can the molecule shown below be properly described as a meso compound?
No
58) Do all primary iodides react with N3- at the same rate via the SN2 mechanism? Explain.
No, not all primary alkyl react with N3- at the same rate via the SN2 mechanism. Some primary iodides are more hindered than others. (CH3)3CCH2I and CH3CH2I are both primary, but (CH3)3CCH2I is significantly more hindered. Additionally, some primary iodides have increased activity due to a benzylic or allylic positioning.
59) Do all primary alkyl iodides undergo SN2 reactions with sodium cyanide in DMSO at identical rates? Explain.
No. All primary iodides are not equally accessible to attack by the CN-. Steric hindrance varies among primary iodides.
Can one predict whether a compound with a single asymmetric carbon is dextro- or levorotatory based on the R/S assignment at this asymmetric carbon? Explain briefly.
No. R/S assignment is purely a convention of nomenclature and is completely independent of the direction in which plane-polarized light is rotated by the compound.
How many asymmetric carbon atoms are present in the following compound?
None
Which of the following statements is (are) true for the compound cis-1,2-dichlorocyclopropane? The compound is chiral The enantiomer of this compound is trans-1,2-dichlorocyclopropane. This compound contains no asymmetric carbons. All of the above None of the above
None of the above
Do you expect the initiation step in the free radical chlorination of 2,2-dimethylpropane to have a positive or negative DS? Explain briefly
One expects a positive DS for this reaction step. A single chlorine molecule is cleaved into two chlorine atoms (chlorine radicals). There is more disorder in the product
56) List the following bromides in order of their increasing reactivity as substrates in SN2 reactions: PhBr, PhCH2Br, and PhCH(CH3)Br.
PhBr < PhCH(CH3)Br < PhCH2Br
74) List the following bromides in order of their increasing reactivity as substrates in SN1 reactions: PhBr, PhCH2Br, and PhCH(CH3)Br.
PhBr < PhCH2Br < PhCH(CH3)Br
52) What type of solvent is best for SN2 reactions which employ anionic nucleophiles: polar, protic solvents; polar, aprotic solvents; or nonpolar solvents? Explain.
Polar, aprotic solvents are best. These solvents have strong dipole moments to enhance solubility of the anionic species but lack the ability to solvate the anion by hydrogen bonding.
Can one separate a mixture of enantiomers by gas chromatography? Explain.
Provided the compounds can be volatilized, a mixture of enantiomers can be separated by GC if an appropriate chiral column can be found. Enantiomers will be retained differently by the chiral stationary phase of the column.
Assign the proper configurational label, R or S, to the chiral carbon in the molecule shown below.
R
Label each asymmetric carbon in the compound below as R or S.
R
In the reaction of Cl2 with ethane and UV light, which of the following reactions would be a chain termination event(s)?
Reaction III
Which of the following statements is the best statement of the Hammond Postulate?
Related species that are similar in energy are also similar in structure
Assign the proper configurational label, R or S, to the chiral carbon in the molecule shown below.
S
Label each asymmetric carbon in the compound below as R or S.
S
______________ are isomers which have the same bonding sequence but differ in the orientation of their atoms in space.
Stereoisomers
Is the mirror image of the following molecule an enantiomer or is it superimposable with it?
Superimposable. The molecule is achiral.
What is the relative reactivity of 2° vs 1° hydrogens in the free radical bromination of n-butane if the ratio of 1-bromobutane to 2-bromobutane formed is 7:93?
The 2° hydrogens are 20 times more reactive than the 1° ones.
Consider the following substitution reaction with a ΔG° value of -91.1 kJ/mole. HO- + CH3Cl ↔ CH3OH + Cl- Given this information which of the following statements must be true? (R = 8.315 J/mole K)
The Keq at 25°C for this reaction is very large, in other words this reaction proceeds to near completion as written, left to right under standard conditions
________ is the minimum kinetic energy reacting molecules must possess to overcome the repulsions between their electron clouds when they collide.
The activation energy or Ea
Which compound has the smaller bond dissociation energy for its carbon-chlorine bond, CH3Cl or (CH3)3CCl? Explain your reasoning.
The carbon-chlorine bond of (CH3)3CCl has the smaller bond dissociation energy. The carbon radical that results upon bond cleavage is a tertiary radical. Tertiary alkyl radicals are more stable than primary due to hyerconjugative or inductive stabilization
120) Which diastereomer of 1-bromo-4-t-butylcyclohexane, the cis or the trans, undergoes elimination more rapidly when treated with sodium ethoxide? Explain your answer.
The cis isomer reacts more quickly. An axial orientation of the C—Br bond is required for E2 in six-membered ring systems. In order for this to occur in the trans isomer, the bulky t-butyl group must also assume an axial orientation; this requires substantial energy of activation.
If possible, draw the structure of the enantiomer of the molecule shown below.
The compound is an achiral, meso compound; it has no enantiomer.
Consider the conversion of X to Z through the sole intermediate Y. Given the reaction-energy diagram shown below, which step is the rate-limiting step? Explain your reasoning
The conversion of Y to Z has a higher Ea than does the conversion of X to Y. The conversion of Y to Z is therefore rate-limiting
The hydrogen atom abstraction step in the free radical bromination of methane is endothermic. Use the Hammond Postulate to speculate on the extent of bond formation and bond cleavage in the transition state.
The endothermic nature of this step means that the energy of the transition state is closer to that of the step's products than to its reactants. Using the Hammond Postulate this means the transition state more closely resembles a carbon radical than a bromine radical. The carbon-hydrogen bond is almost completely broken and the hydrogen-bromine bond completely formed in the transition state.
Which of the following statements correctly describes the contribution of ΔS° to ΔG°?
The entropy term makes a greater contribution to ΔG° at high temperatures.
The hydrogen atom abstraction step in the free radical chlorine of methane is exothermic. Use the Hammond Postulate to speculate on the extent of bond formation and bond cleavage in the transition state
The exothermic nature of this step means that the energy of the transition state is closer to that of the step's reactants than to its products. Using the Hammond Postulate this means the transition state more closely resembles a chlorine radical than a carbon radical. The carbon-hydrogen bond has broken very little and the hydrogen-chlorine bond has formed very little in the transition state.
Use the Hammond Postulate to explain why free radical brominations are more selective than free radical chlorinations
The first propagation step in free radical bromination is endothermic while the analogous step in free radical chlorination is exothermic. From the Hammond Postulate, this means that the transition state for the bromination is product-like (ie, radical-like) while the transition state for the chlorination is reactant-like. The product-like transition state for bromination has the C-H bond nearly broken and a great deal of radical character on the carbon atom. The energy of this transition state reflects most of the energy difference of the radical products. This is not true in the chlorination case where the transition state possesses little radical character.
Explain the significance of the frequency factor A in the Arrhenius equation.
The frequency factor accounts for the number of collisions between reacting molecules and the fraction of these collisions with the proper orientation for the reaction to happen. There is a linear relationship between the number of these collisions and the rate constant of the reaction. For a given reaction A is a constant
Why is the following structure not a meso compound?
The functional group at the top (aldehyde) is different from the bottom (alcohol) and thus there is no internal reflective plane in the molecule.
Do you expect the initiation step in the free radical chlorination of 2,2-dimethylpropane to be endo- or exothermic? Explain briefly, and comment on the sign of DH.
The initiation step of this mechanism is the homolytic bond cleavage of the chlorine-chlorine bond. Energy is required to break a bond. The reaction step is endothermic with a positive DH.
96) Why does CH2 CHCHBrCH3 undergo solvolysis much more rapidly than 2-bromobutane?
The intermediate carbocation is resonance stabilized.
47) Which halide is a better nucleophile, iodide or fluoride? Explain.
The iodide ion is the better nucleophile. The larger size of this ion renders its electron cloud more polarizable.
What is meant by the mechanism of a chemical reaction?
The mechanism of a reaction is the complete, step-by-step description of exactly which bonds break, which bonds form, and the order in which these events occur in the transformation of reactants into products.
Is the molecule shown below chiral or achiral? Explain what this means.
The molecule is chiral because it's mirror image is nonsuperimposable.
Which of the statements below correctly describes an achiral molecule?
The molecule might be a meso form.
Does one expect ΔS° in a propagation step of the free-radical chlorination of methane to be greater than zero, less than zero, or approximately equal to zero? Briefly explain your choice. CH4 + Cl∙ → CH3∙ + HCl CH3∙ + ClCl → CH3Cl + Cl∙
The propagation steps of the free-radical chlorination of methane are shown below. In each of the steps, two reactant molecules generate two product molecules. This similarity in the number of molecular species means that the disorder in the reaction is neither greatly increased nor diminished. Therefore, one expects ΔS° in either propagation step to be approximately equal to zero
Consider the reaction (CH3)3CBr + CH3CH2OH → (CH3) 3COCH2CH3 + HBr. Experimentally one finds that if the concentration of (CH3)3CBr is tripled, the rate of the reaction triples. One also finds that if the concentration of CH3CH2OH is doubled, the rate of the reaction is unchanged. Which of the following correctly describes the kinetics of this reaction?
The reaction is first order overall.
Consider the three-step mechanism for the reaction of A through intermediates B and C to produce D shown below A → B Ea = 15 kcal/mol, ΔH° = 13 kcal/mol B → C Ea = 10 kcal/mol, ΔH° = -6 kcal/mol C → D Ea = 2 kcal/mol, ΔH° = -20 kcal/mol Which of the three steps is rate-limiting?
The reaction of A to B.
Given an activation energy of 15 kcal/mol, use the Arrhenius equation to estimate how much faster the reaction will occur if the temperature is increased from 100°C to 120°C. R = 1.987 cal/mol∙K
The reaction will occur about 2.8 times faster.
Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?
The same compound
Briefly describe how two enantiomers might be separated.
The two compounds can be converted by diastereomers, separated based on physical properties of these diastereomers, and subsequently returned to their original forms after separation. Another method involves the chromatographic separation using a chiral stationary phase.
112) When 1-iodo-1-methylcyclohexane is treated with NaOCH2CH3, the more highly substituted alkene product predominates. When KOC(CH3)3 is used instead, the less highly substituted alkene product predominates. Offer an explanation.
The unhindered ethoxide produces the more stable alkene product (ie, the more highly substituted alkene possible). When the bulky t-butoxide is used, the most accessible hydrogen is removed. This results in the least highly substituted alkene possible.
What accounts for the relatively high stability of the benzyl radical?
The unpaired electron is delocalized through a conjugated pi system.
Explain the stereochemical relationship, if any, among the following two structures and describe whether or not they could be theoretically isolated from each other.
These structures are conformationally dependent diastereomers. They could not be isolated because they are actually the same molecule.
Which of the following statements correctly pertains to a pair of enantiomers?
They rotate the plane of polarized light by exactly the same amount and in opposite directions.
Which of the following statements is (are) true for the compound (R)-2-butanol?
This compound is chiral, optically active, and has an enantiomer.
Which of the following statements is (are) true for the compound (3R,4R)-3,4-dimethylhexane?
This compound is chiral, the enantiomer of this compound is (3S,4S)-3,4-dimethylhexane, the compound is a diastereomer of (3R,4S)-3,4-dimethylhexane.
37) Consider the reaction of (CH3)3CO- with iodomethane. Will the reaction rate increase, decrease, or remain the same if the concentration of iodomethane is increased? Explain.
This is an SN2 reaction with a rate = k [(CH3)3CO-][CH3I]. The reaction rate will increase as [CH3I] increases.
81) When t-butyl chloride undergoes solvolysis in a solvent mixture composed of 70% water/30% acetone, the reaction rate is slower than when the same compound is solvolyzed in 80% water/20% acetone. Explain.
This is purely a solvent effect. The greater the percentage of water in this solvent mixture, the more polar the solvent. The more polar the solvent, the more easily solvated the developing carbocation and the more rapidly it is formed.
If possible, draw the enantiomer of the molecule shown below.
This molecule is achiral. It does not have an enantiomer.
30) When water is shaken with dichloromethane, a two-phase system results. Which compound forms the upper phase? Explain.
Water is less dense than dichloromethane and therefore forms the upper phase.
Can the molecule shown below be properly described as a meso compound?
Yes
Would a 50:50 mixture of (2R,3R)-2,3-dibromobutane and (2R,3S)-2,3-dibromobutane be optically active? Explain.
Yes, the mixture would be optically active. This is not a racemic mixture but a mixture of diastereomers. The specific rotations of diastereomers are not the same in magnitude nor necessarily opposite in sign.
Does the molecule shown below contain asymmetric carbon atoms? Is this molecule chiral?
Yes, the molecule contains 4 asymmetric carbon atoms. No, the molecule is not chiral since it is superimposable with its mirror image.
Is it theoretically possible to separate the pair of compounds below by distillation? Explain briefly.
Yes. The molecules are related as diastereomers and hence have different boiling points.
Can a molecule be chiral if it contains no asymmetric carbons? Explain briefly.
Yes. The presence of asymmetric carbons is not required for a molecule to be chiral. The only requirement is that the molecule be nonsuperimposable with its mirror image. Structural features other than asymmetric carbons can lead to chirality.
Predict the specific rotation of the compound shown.
Zero; the compound is achiral
42) Provide the structure of the major organic product in the following reaction. (CH3)3N + CH3CH2CH2I →
[(CH3)3NCH2CH2CH3]+ I-
What reactive species is produced in the initiation step of the free radical chlorination of 2,2-dimethylpropane?
a chlorine atom
When two carbenes collide, they immediately dimerize to give ________.
an alkene
How do alkyl substituents stabilize a carbocationic center to which they are attached?
both A and C
Given the chlorination of acetone shown below, choose the correct rate law. CH3COCH3 + Cl2 → CH3COCH2Cl + HCl
cannot be determined from stoichiometry; must be determined experimentally
Which of the following reactive intermediates can best be described as both nucleophilic and strongly basic?
carbanions
76) List the following bromides in order of their increasing reactivity as substrates in SN1 reactions: 1-iodo-1-ethylcyclopentane, chlorocyclopentane, and iodocyclopentane.
chlorocyclopentane < iodocyclopentane < 1-iodo-1-ethylcyclopentane
9) Provide an acceptable name for the compound shown below.
cis-1, 2-dichlorocyclopentane
Stereoisomers which are not mirror image isomers are _________.
diastereomers
Which of the following terms best describes the stereochemical relationship of the two compounds shown below in Fischer notation?
diastereomers
Which is a measure of the randomness of a system?
entropy
Which of the halogens below undergoes free radical halogenation with ethane most rapidly?
fluorine
The bond dissociation energy is the amount of energy required to break a bond ________.
homolytically
Which of the following reactive intermediate species maintains sp3 hybridization?
methyl carbanion
73) Arrange the following compounds in order of increasing reactivity toward ethanol solvolysis: t-butyl bromide, t-butyl iodide, isopropyl chloride, methyl iodide.
methyl iodide < isopropyl chloride < t-butyl bromide < t-butyl iodide
Species with unpaired electrons are called ________.
radicals or free radicals
Consider the elementary step in the solvolysis of isopropyl chloride shown below and write the rate equation for this step (CH3)2CHCl → (CH3)2CH+ + Cl-
rate = k[(CH3)2CHCl]
The following reaction occurs readily: Experimentally one finds that if the concentration of I- is doubled, the rate doubles. Also if the concentration of CH3Br is halved, the rate is halved. What is the rate equation for this reaction?
rate = k[CH3Br][I-]
Consider the bond dissociation energies listed below in kcal/mol. CH3-Br 70 CH3CH2-Br 68 (CH3)2CH-Br 68 (CH3)3C-Br 65 These data show that the carbon-bromine bond is weakest when bromine is bound to a ________.
tertiary carbon
The rate of a reaction typically increases as the temperature increases because:
the fraction of molecules with kinetic energy greater than Ea increases.
Which of the following correctly expresses the standard Gibbs free energy change of a reaction in terms of the changes in enthalpy and entropy?
ΔG° = ΔH° - TΔS°
If a reaction is exothermic, then:
ΔH° < 0
Which of the following is true for the termination step of a free radical chlorination reaction?
ΔH° < 0 and ΔS° < 0
Which of the following is true for the initiation step of a free radical chlorination reaction?
ΔH° > 0 and ΔS° > 0
The hydrogenation of acetylene to produce ethane is shown below. Is ΔS° for this reaction positive, negative, or impossible to predict? Explain your reasoning C2H2 (g) + 2H2 (g) → C2H6 (g)
ΔS° < 0. The three reactant molecules have significantly more freedom of motion, and randomness, than does the single molecule of product into which they are converted.
Which of the following is not a possible termination step in the free radical chlorination of methane?
∙CH3 + Cl2 → CH3Cl + Cl∙
Which of the following is a propagation step in the free radical chlorination of dichloromethane?
∙CHCl2 + Cl2 → CHCl3 + Cl∙
When the reaction between methane and chlorine is photochemically initiated, which of the following compounds cannot be formed through a termination reaction?
HCl
Which H atom in the molecule shown will be most readily abstracted by a bromine radical?
Hc
Which of the structures above are meso structures?
I
Rank the free radicals (I-III) shown below in order of decreasing stability (i.e., from most stable to least stable)
I > III > II
Which of the following incorrectly describes cis-1,2-dimethylcyclopentane?
It has an enantiomer.
________ is the study of reaction rates.
Kinetics
Captopril is used to treat high blood pressure and congestive heart failure. Label the chiral centers as R or S.
Look at picture
Circle all structures shown below that are chiral.
Look at picture
Circle each chiral molecule among those shown below.
Look at picture
