Question 91: Physical Properties – Intermolecular Forces
Which haloalkane exhibits hydrogen bonding?
A) CH₃Cl
B) CH₃CH₂Cl
C) (CH₃)₂CHCl
D) (CH₃)₃CCl
Answer: A) CH₃Cl
Explanation:
Hydrogen bonding occurs when hydrogen is directly bonded to highly electronegative atoms like nitrogen, oxygen, or fluorine. In haloalkanes, chlorine is sufficiently electronegative to allow for hydrogen bonding in smaller haloalkanes. CH₃Cl can form hydrogen bonds due to the presence of the hydrogen atom bonded to carbon, which is attached to the electronegative chlorine, making it capable of weak hydrogen bonding interactions.
Question 92: Nomenclature
What is the IUPAC name for CH₃-CH₂-CH₂-Br?
A) 1-Bromopropane
B) 2-Bromopropane
C) 1-Bromo-2-propane
D) 3-Bromopropane
Answer: A) 1-Bromopropane
Explanation:
Identify the longest carbon chain, which is three carbons (propane). The bromine is attached to the first carbon, so the correct name is 1-Bromopropane.
Question 93: Physical Properties – Boiling Point
Which haloalkane has the lowest boiling point?
A) CH₃Cl
B) CH₃CH₂Cl
C) CH₃CH₂CH₂Cl
D) (CH₃)₃CCl
Answer: A) CH₃Cl
Explanation:
Boiling points increase with molecular size and intermolecular forces. CH₃Cl (methyl chloride) is the smallest haloalkane among the options and thus has the lowest boiling point due to weaker van der Waals forces.
Question 94: Reactions – SN1 Mechanism
Which haloalkane is most likely to undergo an SN1 reaction?
A) CH₃Cl
B) CH₃CH₂Cl
C) (CH₃)₂CHCl
D) (CH₃)₃CCl
Answer: D) (CH₃)₃CCl
Explanation:
SN1 reactions are favored by tertiary haloalkanes due to the stability of the carbocation intermediate. (CH₃)₃CCl is a tertiary chloride and thus most likely to undergo an SN1 reaction.
Question 95: Reactions – SN2 Mechanism
Which haloalkane is least likely to undergo an SN2 reaction?
A) CH₃I
B) CH₃CH₂Br
C) (CH₃)₂CHCl
D) (CH₃)₃CBr
Answer: D) (CH₃)₃CBr
Explanation:
SN2 reactions are hindered by steric hindrance. (CH₃)₃CBr is a tertiary haloalkane with significant steric hindrance, making it the least likely to undergo an SN2 reaction.
Question 96: Nomenclature – Substituted Haloarenes
What is the IUPAC name for 3-chlorotoluene?
A) 3-Chloromethylbenzene
B) 1-Chloro-3-methylbenzene
C) 3-Chloro-1-methylbenzene
D) 1-Methyl-3-chlorobenzene
Answer: D) 1-Methyl-3-chlorobenzene
Explanation:
In substituted haloarenes, the substituents are named with their positions. 3-Chlorotoluene translates to 1-Methyl-3-chlorobenzene, indicating a methyl group at position 1 and a chlorine at position 3 on the benzene ring.
Question 97: Reactions – Hydrohalogenation
What is the product when 2-methylpropene undergoes hydrohalogenation with HBr?
A) 2-Bromo-2-methylpropane
B) 1-Bromo-2-methylpropane
C) 2-Bromo-1-methylpropane
D) 1-Bromo-3-methylpropane
Answer: A) 2-Bromo-2-methylpropane
Explanation:
Hydrohalogenation follows Markovnikov’s rule, where the hydrogen atom attaches to the carbon with more hydrogen atoms, and the halogen attaches to the more substituted carbon. Thus, 2-methylpropene reacts with HBr to form 2-Bromo-2-methylpropane.
Question 98: Properties – Reactivity Order
Arrange the following haloalkanes in order of increasing reactivity towards nucleophilic substitution (SN2): CH₃Br, CH₃CH₂Br, (CH₃)₂CHBr, (CH₃)₃CBr.
A) (CH₃)₃CBr < (CH₃)₂CHBr < CH₃CH₂Br < CH₃Br
B) CH₃Br < CH₃CH₂Br < (CH₃)₂CHBr < (CH₃)₃CBr
C) (CH₃)₂CHBr < (CH₃)₃CBr < CH₃Br < CH₃CH₂Br
D) CH₃CH₂Br < CH₃Br < (CH₃)₂CHBr < (CH₃)₃CBr
Answer: A) (CH₃)₃CBr < (CH₃)₂CHBr < CH₃CH₂Br < CH₃Br
Explanation:
SN2 reactivity decreases with increasing steric hindrance. (CH₃)₃CBr (tertiary) is least reactive, followed by (CH₃)₂CHBr (secondary), CH₃CH₂Br (primary), and CH₃Br (methyl) being the most reactive.
Question 99: Reactions – Elimination (E2)
Which product is formed when 2-bromo-2-methylpropane undergoes E2 elimination?
A) 2-Methylpropene
B) 1-Methylpropene
C) 2,3-Dimethylpropene
D) 1,2-Dimethylpropene
Answer: A) 2-Methylpropene
Explanation:
E2 elimination leads to the formation of the most stable alkene. 2-Bromo-2-methylpropane eliminates a hydrogen and bromine from adjacent carbons to form 2-Methylpropene, the most stable tertiary alkene.
Question 100: Nomenclature – Haloarenes
What is the IUPAC name for p-fluorotoluene?
A) 1-Fluoro-4-methylbenzene
B) 4-Fluoro-1-methylbenzene
C) Both A and B
D) 1-Methyl-4-fluorobenzene
Answer: C) Both A and B
Explanation:
Both 1-Fluoro-4-methylbenzene and 4-Fluoro-1-methylbenzene are correct IUPAC names for p-fluorotoluene, as the numbering can start from either substituent to give the lowest possible numbers.
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