Question 81: Reactions – Preparation of Methyl Halides
Which reagent is used to convert methanol to methyl chloride?
A) HCl
B) PCl₅
C) SOCl₂
D) All of the above
Answer: D) All of the above
Explanation:
Methanol can be converted to methyl chloride using HCl, PCl₅, or SOCl₂ through substitution reactions.
Question 82: Properties – Reactivity in E1 Mechanism
Which haloalkane is most likely to undergo E1 elimination?
A) CH₃CH₂Cl
B) (CH₃)₂CHCl
C) (CH₃)₃CCl
D) CH₃Cl
Answer: C) (CH₃)₃CCl
Explanation:
(CH₃)₃CCl (tert-Butyl chloride) readily undergoes E1 elimination due to the formation of a stable tertiary carbocation.
Question 83: Nomenclature – Haloalkanes with Branches
What is the IUPAC name for (CH₃)₂CH-CH₂-Br?
A) 1-Bromo-2-methylpropane
B) 2-Bromo-2-methylpropane
C) 1-Bromo-3-methylpropane
D) 3-Bromo-1-methylpropane
Answer: A) 1-Bromo-2-methylpropane
Explanation:
Number the chain to give the substituent the lowest possible number. Bromine is on carbon 1 and the methyl group on carbon 2, resulting in 1-Bromo-2-methylpropane.
Question 84: Reactions – Effect of Leaving Group
Which haloalkane has the best leaving group for substitution reactions?
A) CH₃F
B) CH₃Cl
C) CH₃Br
D) CH₃I
Answer: D) CH₃I
Explanation:
Iodide (I⁻) is the best leaving group among the halides due to its large size and weak base strength, making CH₃I the best for substitution reactions.
Question 85: Physical Properties – Polarity
Which haloalkane is nonpolar?
A) CH₃Cl
B) CH₃CH₂Cl
C) (CH₃)₃CCl
D) None of the above
Answer: D) None of the above
Explanation:
All haloalkanes have polar C-X bonds, making them polar molecules. Hence, none are completely nonpolar.
Question 86: Nomenclature – Common vs IUPAC Names
What is the common name for 2,2-dichloropropane?
A) Propylene dichloride
B) Propan-2,2-dichloride
C) Both A and B
D) Propane-2,2-dichloride
Answer: C) Both A and B
Explanation:
Both Propylene dichloride and Propan-2,2-dichloride are accepted names for 2,2-Dichloropropane.
Question 87: Reactions – SN1 Mechanism
Which of the following conditions favor the SN1 mechanism in haloalkane reactions?
A) Primary haloalkane, polar aprotic solvent
B) Tertiary haloalkane, polar protic solvent
C) Methyl haloalkane, non-polar solvent
D) Secondary haloalkane, high concentration of nucleophile
Answer: B) Tertiary haloalkane, polar protic solvent
Explanation:
SN1 is favored by tertiary haloalkanes and polar protic solvents that stabilize the carbocation intermediate.
Question 88: Properties – Comparison with Alcohols
Compared to corresponding alcohols, haloalkanes have:
A) Higher boiling points
B) Lower boiling points
C) Similar boiling points
D) Variable boiling points
Answer: B) Lower boiling points
Explanation:
Haloalkanes have lower boiling points than corresponding alcohols because they can only engage in dipole-dipole interactions, whereas alcohols can form hydrogen bonds, leading to higher boiling points.
Question 89: Nomenclature – Priority of Substituents
In 3-bromo-2-chloropentane, which substituent has priority in numbering?
A) Bromine
B) Chlorine
C) Both have equal priority
D) It depends on the alphabetical order
Answer: C) Both have equal priority
Explanation:
When substituents have equal priority, numbering is done to give the lowest set of locants, not based on alphabetical order.
Question 90: Reactions – Competitive Reactions
In the reaction of 2-bromopropane with NaOH, which product is major?
A) 2-Propanol
B) Propene
C) 1-Propanol
D) No reaction
Answer: A) 2-Propanol
Explanation:
With a secondary haloalkane and NaOH, nucleophilic substitution (SN2 or SN1) predominates, forming 2-Propanol as the major product.
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