Chapter 7 Flashcards
Which of the following statements best describes the relative bond dissociation energies of the sigma and pi bonds present in the carbon-carbon double bond of an alkene?
A) sigma > pi
B) pi > sigma
C) sigma = pi
D) cannot be estimated
A) sigma > pi
The carbon-carbon bond length in ethylene is ________ than the carbon-carbon bond length in ethane, and the HCH bond angle in ethylene is ________ the HCH bond angle in ethane
A) shorter; smaller than
B) shorter; larger than
C) longer; smaller than
D) longer; larger than
E) longer; the same as
B) shorter; larger than
Carbon-carbon single bonds tend to be ________ and ________ than carbon-carbon double bonds.
A) shorter, stronger
B) longer, stronger
C) shorter, weaker
D) longer, weaker
D) longer, weaker
Which of the following best approximates the CCC bond angle of propene?
A) 90° B) 109° C) 120° D) 150° E) 180°
C) 120°
What two atomic orbitals or hybrid atomic orbitals overlap to form the CH bond in ethylene?
A) C sp3 + H s
B) C sp2 + H s
C) C sp + H s
D) C p + H s
B) C sp2 + H s
What two atomic orbitals or hybrid atomic orbitals overlap to form the CC σ bond in ethylene?
A) C sp3 + C sp3 B) C sp3 + C sp2 C) C sp2 + C sp2 D) C sp3 + C p E) C sp2 + C p
C) C sp2 + C sp2
What two atomic orbitals or hybrid atomic orbitals overlap to form the CC π bond in ethylene?
A) C sp3 + C sp3 B) C sp3 + C sp2 C) C sp2 + C sp2 D) C sp2 + C p E) C p + C p
E) C p + C p
The compound produced when 3-methylpent-2-ene undergoes hydrogenation in the presence of a platinum catalyst is ________.
3-methylpentane
Using Zaitsev’s rule, choose the most stable alkene among the following.
A) 1-methylcyclohexene
B) 3-methylcyclohexene
C) 4-methylcyclohexene
D) They are all of equal stability according to Zaitsev’s rule.
A) 1-methylcyclohexene
Using Zaitsev’s rule, choose the most stable alkene among the following.
A) hex-1-ene
B) (E)-hex-2-ene
C) (Z)-hex-2-ene
D) They are all of equal stability according to Zaitsev’s rule.
B) (E)-hex-2-ene
Using Zaitsev’s rule, choose the most stable alkene among the following.
A) 1,2-dimethylcyclohexene
B) 1,6-dimethylcyclohexene
C) cis-3,4-dimethylcyclohexene
D) They are all of equal stability according to Zaitsev’s rule.
A) 1,2-dimethylcyclohexene
Consider the constitutional isomers 2-methylbut-1-ene, 2-methylbut-2-ene, and 3-methylbut-1-ene. When each of these alkenes is subjected to catalytic hydrogenation (H2, Pt), a single product results. Which of the following best describes the structural relationship among these products?
A) The products are cis-trans isomers. B) The products are identical. C) The products are constitutional isomers. D) The products are enantiomers. E) The products are diastereomers.
B) The products are identical.
Which of the following alkenes has the largest molar heat of hydrogenation (ie, releases the most heat upon hydrogenation)?
A) 2,3-dimethyl-2-butene B) 2-methyl-2-butene C) trans-2-butene D) cis-2-butene E) 1-hexene
E) 1-hexene
Which of the following alkenes has the smallest molar heat of hydrogenation (ie, releases the least heat upon hydrogenation)?
A) 2,3-dimethyl-2-butene B) 2-methyl-2-butene C) trans-2-butene D) cis-2-butene E) 1-hexene
A) 2,3-dimethyl-2-butene
The trans isomers of cycloalkenes with rings containing fewer than ________ atoms are unstable at room temperature.
8
Which sequence ranks the following compounds in order of increasing heat of hydrogenation,
ΔHhyd?
1) cis-2-butene 2) 1-butene 3) cyclohexene
A) 3
Alkenes ________.
A) are relatively polar compounds B) have lower boiling points than alcohols of similar molecular weight C) are reasonably soluble in water D) both A and B E) none of the above
B) have lower boiling points than alcohols of similar molecular weight
Which of the alkyl chlorides listed below undergoes dehydrohalogenation in the presence of a strong base to give pent-2-ene as the only alkene product?
A) 1-chloropentane B) 2-chloropentane C) 3-chloropentane D) 1-chloro-2-methylbutane E) 1-chloro-3-methylbutane
C) 3-chloropentane
Dehydrohalogenation of 2-bromobutane in the presence of a strong base proceeds via which of the following mechanistic pathways?
A) SN1 B) SN2 C) E1 D) E2 E) none of the above
D) E2
Dehydrohalogenation of an alkyl halide by treating it with a strong base to yield an alkene product typically occurs by what reaction mechanism?
A) SN1 B) SN2 C) E1 D) E2 E) free radical
D) E2
88) Which of the following alkenes is the major product when 2-bromo-2-methylpentane is treated with sodium ethoxide in ethanol?
A) 2-methylpent-1-ene B) 2-methylpent-2-ene C) (E)-4-methylpent-2-ene D) (Z)-4-methylpent-2-ene E) 4-methylpent-1-ene
B) 2-methylpent-2-ene
89) Which of the following alkenes is the major product when 2-bromo-2-methylpentane is treated with potassium tert-butoxide in tert-butanol?
A) 2-methylpent-1-ene B) 2-methylpent-2-ene C) (E)-4-methylpent-2-ene D) (Z)-4-methylpent-2-ene E) 4-methylpent-1-ene
A) 2-methylpent-1-ene
Which of the following statements applies to the E2 mechanism?
A) It occurs with inversion of stereochemistry.
B) It occurs with racemization of stereochemistry.
C) It proceeds through the more stable carbocation intermediate.
D) The C-H and C-X bonds that break must be anti.
E) Use of a bulky base gives the more highly substituted alkene product.
D) The C-H and C-X bonds that break must be anti.
Provide the name of the major alkene product that results when (2S,3S)-2-bromo-3-methylpentane is treated with sodium methoxide in methanol.
(E)-3-methyl-2-pentene
Provide the name of the major alkene product that results when (2S,3R)-2-bromo-3-methylpentane is treated with sodium methoxide in methanol.
(Z)-3-methyl-2-pentene
Provide the name of the major alkene product that results when (2R,3R)-2,3-dibromopentane is treated with zinc in acetic acid.
(Z)-2-pentene
Provide the name of the major alkene product that results when (2S,3R)-2,3-dibromopentane is treated with zinc in acetic acid.
(E)-2-pentene
By what mechanism does cyclohexanol react when treated in sulfuric acid and what compound results?
A) E1; methoxycyclohexane B) E2; methoxycyclohexane C) SN1; methoxycyclohexane D) E2; cyclohexene E) E1; cyclohexene
E) E1; cyclohexene
In the group shown below, which of the following alcohols is (are) likely to yield a product where skeletal rearrangement has occurred when treated with sulfuric acid?
3-methyl-3-pentanol, 3,3-dimethyl-2-butanol, 2,2-dimethylcyclohexanol
A) 3-methyl-3-pentanol only
B) 3,3-dimethyl-2-butanol only
C) 2,2-dimethylcyclohexanol only
D) both 3,3-dimethyl-2-butanol and 2,2-dimethylcyclohexanol
E) None of these three alcohols is prone to rearrangement.
D) both 3,3-dimethyl-2-butanol and 2,2-dimethylcyclohexanol
Which of the following alkenes can show geometric isomerism: 2,3-dichloro-2-pentene, 4-chloro-3-ethyl-3-hexene, 3-chloro-2-methyl-2-butene, and 3-chloro-2-methyl-1-butene?
2,3-dichloro-2-pentene
The compound produced when 3-methylpent-2-ene undergoes hydrogenation in the presence of a platinum catalyst is ________.
3-methylpentane
Which has the smaller heat of hydrogenation, (E)-2-pentene or (Z)-2-pentene? What is the structural origin of this difference?
E)-2-pentene has the smaller heat of hydrogenation. There is less steric strain between the alkyl substituents in the (E)-isomer than in the (Z)-isomer.
Which has the higher boiling point, cis- or trans-hex-3-ene? Briefly explain your choice.
Cis-Hex-3-ene has the higher boiling point since it has a net molecular dipole moment while the trans-isomer does not. The presence of a permanent molecular dipole allows for stronger intermolecular attractions.
Provide the name of the major alkene product that results when (2S,3S)-2-bromo-3-methylpentane is treated with sodium methoxide in methanol.
E)-3-methyl-2-pentene
