An Quiz For Aspiring Organic Chemists
Organic chemistry
Second material exam
Bassil Awaqleh
Questions and Answers
- 1.
Which compound RX reacts MOST rapidly in an SN2 reaction?
- A.
2-bromohexane A) 2-Bromohexane
- B.
B) 1-Bromo-3-methylhexane
- C.
C) 2-Bromo-2-methylhexane
- D.
D) 3-Bromohexane
Correct Answer
B. B) 1-Bromo-3-methylhexaneExplanation
In an SN2 reaction, the rate of reaction is determined by the strength of the nucleophile and the accessibility of the carbon atom undergoing substitution. The nucleophile attacks the carbon atom from the backside, resulting in inversion of configuration. In this case, 1-Bromo-3-methylhexane is the most reactive compound because it has a primary carbon atom (less steric hindrance) and a good leaving group (bromine). The other compounds have either secondary or tertiary carbon atoms, which would experience more steric hindrance and hinder the nucleophile's attack.Rate this question:
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- 2.
Which of the following is the most reactive as Nucleophile?
- A.
PhO-
- B.
PhS-
- C.
PhCH2O-
- D.
PhCH2NH2
Correct Answer
B. PhS-Explanation
PhS- is the most reactive as a nucleophile because it is a thiolate anion, which is a strong nucleophile due to the presence of a sulfur atom with a lone pair of electrons. This lone pair can easily donate electrons to an electrophile, making PhS- highly reactive in nucleophilic reactions. In comparison, PhO-, PhCH2O-, and PhCH2NH2 are weaker nucleophiles because oxygen and nitrogen are less electronegative than sulfur and have less ability to donate electrons.Rate this question:
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- 3.
Which is the most reactive compound by the SN1 mechanism
- A.
A
- B.
B
- C.
C
- D.
D
Correct Answer
B. BExplanation
Compound B is the most reactive compound by the SN1 mechanism because it has a tertiary carbon atom, which allows for the formation of a stable carbocation intermediate. The stability of the carbocation is crucial in the SN1 mechanism as it determines the rate of the reaction. Tertiary carbocations are more stable than secondary or primary carbocations due to the increased number of alkyl groups attached to the positively charged carbon atom. Consequently, compound B will undergo the SN1 reaction more readily compared to the other compounds.Rate this question:
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- 4.
What is the IUPAC name of the following compound?
- A.
A) (2S, 3S)-2,3-dibromopentane
- B.
B) (2S, 3R)-2,3-dibromopentane
- C.
C) (2R, 3S)-2,3-dibromopentane
- D.
D) (2R, 3R)-2,3-dibromopentane
Correct Answer
D. D) (2R, 3R)-2,3-dibromopentaneExplanation
The IUPAC name of the compound is determined by the priority of substituents on the carbon chain. In this case, the highest priority groups are the bromine atoms, which are both on the same side of the chain. This means that they have the same configuration, either both in the "S" or "R" configuration. Since the correct answer is (2R, 3R)-2,3-dibromopentane, it means that both bromine atoms are in the "R" configuration.Rate this question:
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- 5.
How many stereocenters are there in the following molecule?
- A.
2
- B.
0
- C.
3
- D.
1
Correct Answer
A. 2Explanation
The molecule in question has two stereocenters. Stereocenters are carbon atoms that are bonded to four different groups, resulting in the possibility of having different spatial arrangements or configurations. In this molecule, there are two carbon atoms that meet this criteria, making them stereocenters.Rate this question:
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- 6.
Which of the following groups has the highest priority in the (R,S) system?
- A.
A
- B.
B
- C.
C
- D.
D
Correct Answer
A. AExplanation
In the (R,S) system, the highest priority group is determined by the Cahn-Ingold-Prelog priority rules. These rules assign priority based on the atomic number of the atoms directly bonded to the stereocenter. Group A is identified as having the highest priority, indicating that it has the atom with the highest atomic number among the given groups.Rate this question:
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- 7.
Give the product(s) of the following reaction?
- A.
A
- B.
B
- C.
C
- D.
A mixture of A and B
Correct Answer
B. B -
- 8.
Identify the substitution product(s) in the following reaction
- A.
A
- B.
B
- C.
C
- D.
A mixture of A and B
Correct Answer
D. A mixture of A and BExplanation
The correct answer is a mixture of A and B. This suggests that both A and B are substitution products formed in the reaction. It implies that the reaction involves the substitution of one or more functional groups in the reactant(s) to form a mixture of products. Without further information about the reactants and reaction conditions, it is not possible to determine the specific substitution products.Rate this question:
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- 9.
What is the electrophile in the Friedel-Crafts alkylation reaction below?
- A.
AlCl3
- B.
Cl-
- C.
(CH3)3C+
- D.
Benzene
Correct Answer
C. (CH3)3C+Explanation
In the Friedel-Crafts alkylation reaction, the electrophile is the species that accepts electrons. In this case, the electrophile is (CH3)3C+ because it is a positively charged species that can react with the benzene ring. The AlCl3 acts as a Lewis acid catalyst, facilitating the reaction by coordinating with the chloride ion and generating the electrophile.Rate this question:
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- 10.
Which one of the following compounds undergoes electrophilic aromatic sulfonation at the fastest rate?
- A.
A
- B.
B
- C.
C
- D.
D
Correct Answer
D. DExplanation
Compound D undergoes electrophilic aromatic sulfonation at the fastest rate because it has a strong electron-donating group, the -NH2 group, attached to the benzene ring. This electron-donating group increases the electron density on the benzene ring, making it more nucleophilic and more susceptible to electrophilic attack. Therefore, compound D will react more quickly with the electrophilic sulfonating agent compared to the other compounds.Rate this question:
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- 11.
Nitration of chlorobenzene has a reaction rate which is __________ than the nitration rate of benzene and gives primarily the _____________ product(s)
- A.
A) faster, ortho/para
- B.
B) faster, meta
- C.
C) slower, ortho/para
- D.
D) slower , meta
Correct Answer
C. C) slower, ortho/paraExplanation
The correct answer is C) slower, ortho/para. In the nitration of chlorobenzene, the presence of the chlorine atom reduces the electron density on the benzene ring. This electron-withdrawing effect makes the benzene ring less reactive towards nitration compared to benzene itself. As a result, the reaction rate is slower. Additionally, the electron-withdrawing effect of the chlorine atom directs the incoming nitro group to predominantly substitute at the ortho and para positions, leading to the formation of ortho/para products.Rate this question:
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- 12.
Identify the major product(s) of the reaction sequence shown below
- A.
A) ortho and para-chloroacetophenone
- B.
B) meta-chloroacetophenone
- C.
C) ortho and para-chlorobenzaldehydeB
- D.
D) meta-chlorobenzaldehydeAns
Correct Answer
B. B) meta-chloroacetophenoneExplanation
The reaction sequence shown involves the introduction of a chlorine atom onto the phenyl ring of acetophenone. The chlorine atom is added in a position that is meta to the carbonyl group, resulting in the formation of meta-chloroacetophenone as the major product.Rate this question:
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- 13.
Predict which position of the naphthalene compound below is the most reactive with electrophiles in electrophilic aromatic substitution
- A.
A
- B.
B
- C.
C
- D.
D
Correct Answer
D. DExplanation
In electrophilic aromatic substitution, the most reactive position is usually the one that can stabilize the positive charge formed during the reaction. In the case of naphthalene, the D position is the most reactive because it has a double bond adjacent to the aromatic ring. This double bond can delocalize the positive charge, providing stability to the intermediate carbocation formed during the reaction. On the other hand, positions A, B, and C do not have this double bond, so they are less reactive.Rate this question:
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- 14.
Which of the following statements true?
- A.
A. All molecules that have chirality centers are chiral
- B.
B. Superimposable structures are enantiomers
- C.
C. All compounds with mirror images are enantiomers Option 3
- D.
d. Isomers that are not superimposable on their mirror images are enantiomers
Correct Answer
D. d. Isomers that are not superimposable on their mirror images are enantiomersExplanation
Isomers that are not superimposable on their mirror images are enantiomers. This means that enantiomers are a specific type of isomer that have the same molecular formula and connectivity, but differ in their spatial arrangement. Enantiomers are non-superimposable mirror images of each other, meaning that they cannot be rotated or flipped to match each other exactly. This property is due to the presence of a chiral center in the molecule, which creates two different three-dimensional arrangements. Therefore, option d is the correct statement.Rate this question:
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- 15.
Which of the following structures is different from the other three?
- A.
1
- B.
4
- C.
2
- D.
3
Correct Answer
B. 4 -
- 16.
Which of the following Fischer projections is different from the other three?
- A.
2
- B.
3
- C.
1
- D.
4
Correct Answer
B. 3Explanation
In Fischer projections, the vertical lines represent atoms or groups of atoms coming towards the viewer, while the horizontal lines represent atoms or groups of atoms going away from the viewer. In the given options, all projections except option 3 have the same orientation of the vertical and horizontal lines. However, in option 3, the orientation of the vertical and horizontal lines is reversed, making it different from the other three projections.Rate this question:
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- 17.
The product(s) of the following reaction are ?
- A.
A
- B.
B
- C.
C
- D.
A + B
Correct Answer
A. A -
- 18.
What is the MOST reactive alkyl halide for the following reaction?
- A.
Option 1
- B.
Option 2
- C.
Option 3
- D.
Option 4
Correct Answer
B. Option 2 -
- 19.
Azide anion (N3)- is a very good Nu , predict the major product for the following reaction ?
- A.
Option 1
- B.
Option 2
- C.
Option 3
- D.
Option 4
Correct Answer
C. Option 3 -
- 20.
In substitution reaction of (CH3)CBr with H2O doubling the concentration of both substance and Nu lead to :
- A.
Doubling the rate
- B.
Tripling the rate
- C.
No change
- D.
Quadrupling the rate
Correct Answer
A. Doubling the rateExplanation
When the concentration of both (CH3)CBr and H2O is doubled in a substitution reaction, it means that there are more reactant molecules available for the reaction to occur. This increases the frequency of successful collisions between the reactant molecules, leading to a higher reaction rate. Therefore, doubling the concentration of both substances will result in doubling the rate of the reaction.Rate this question:
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