Question 31: Physical Properties – Vapor Pressure
Which haloalkane has the highest vapor pressure at room temperature?
A) CH₃Cl
B) CH₃CH₂Cl
C) C₂H₅CHCl₂
D) (CH₃)₃CCl
Answer: D) (CH₃)₃CCl
Explanation:
Higher molecular weight and branching (as in (CH₃)₃CCl) generally lead to lower boiling points and higher vapor pressures.
Question 32: Nomenclature – Substituent Priority
What is the correct IUPAC name for CH₃-CH(Br)-CH₂-Cl?
A) 1-Bromo-3-chloropropane
B) 2-Bromo-1-chloropropane
C) 1-Chloro-3-bromopropane
D) 3-Chloro-1-bromopropane
Answer: B) 2-Bromo-1-chloropropane
Explanation:
Number the chain to give the substituents the lowest possible numbers. Chlorine gets position 1 and bromine position 2, resulting in 2-Bromo-1-chloropropane.
Question 33: Reactions – Halogenation Specificity
Which haloalkane is formed when ethylene reacts with chlorine?
A) Ethyl chloride
B) 1,2-Dichloroethane
C) Vinyl chloride
D) Ethanol
Answer: B) 1,2-Dichloroethane
Explanation:
Addition of chlorine to ethylene (an alkene) yields 1,2-Dichloroethane through an addition reaction.
Question 34: Properties – Reactivity Order
Arrange the following haloalkanes in order of decreasing reactivity towards SN2 reactions: CH₃Cl > CH₃CH₂Cl > (CH₃)₂CHCl > (CH₃)₃CCl
A) CH₃Cl > CH₃CH₂Cl > (CH₃)₂CHCl > (CH₃)₃CCl
B) (CH₃)₃CCl > (CH₃)₂CHCl > CH₃CH₂Cl > CH₃Cl
C) CH₃CH₂Cl > CH₃Cl > (CH₃)₂CHCl > (CH₃)₃CCl
D) CH₃Cl > (CH₃)₂CHCl > CH₃CH₂Cl > (CH₃)₃CCl
Answer: A) CH₃Cl > CH₃CH₂Cl > (CH₃)₂CHCl > (CH₃)₃CCl
Explanation:
SN2 reactivity decreases with increasing steric hindrance. Methyl chloride (CH₃Cl) is the most reactive, followed by primary, secondary, and then tertiary haloalkanes.
Question 35: Nomenclature – Binary Halo Compounds
Which of the following is the correct name for C₂H₅Cl?
A) Ethyl chloride
B) 1-Chloroethane
C) Both A and B
D) Dichloroethane
Answer: C) Both A and B
Explanation:
Both Ethyl chloride and 1-Chloroethane are correct IUPAC names for C₂H₅Cl.
Question 36: Reactions – Substitution Mechanism
Which mechanism is predominantly followed by tertiary haloalkanes in nucleophilic substitution?
A) SN1
B) SN2
C) E1
D) E2
Answer: A) SN1
Explanation:
Tertiary haloalkanes favor the SN1 mechanism due to the stability of the tertiary carbocation intermediate.
Question 37: Physical Properties – Boiling Point Trend
Which statement correctly describes the boiling point trend of haloalkanes?
A) Boiling points decrease with increasing molecular weight
B) Boiling points increase with increasing molecular weight
C) Boiling points remain the same irrespective of molecular weight
D) Boiling points are independent of molecular structure
Answer: B) Boiling points increase with increasing molecular weight
Explanation:
As molecular weight increases, so do London dispersion forces, leading to higher boiling points.
Question 38: Nomenclature – Prefixes and Suffixes
What is the IUPAC name for CH₃-CH₂-CH₂-CH₂-Br?
A) 1-Bromobutane
B) 2-Bromobutane
C) 3-Bromobutane
D) Butyl bromide
Answer: A) 1-Bromobutane
Explanation:
The bromine is attached to the first carbon of the four-carbon chain, so the correct name is 1-Bromobutane.
Question 39: Reactions – Solvent Effects
Which solvent favors the SN2 reaction mechanism for haloalkanes?
A) Polar protic
B) Polar aprotic
C) Non-polar
D) Any solvent
Answer: B) Polar aprotic
Explanation:
Polar aprotic solvents stabilize cations but do not solvate anions effectively, enhancing nucleophilicity and favoring the SN2 mechanism.
Question 40: Properties – Reactivity Order in SN1
Arrange the following haloalkanes in order of decreasing reactivity towards SN1 reactions: (CH₃)₃CCl > (CH₃)₂CHCl > CH₃CH₂Cl > CH₃Cl
A) (CH₃)₃CCl > (CH₃)₂CHCl > CH₃CH₂Cl > CH₃Cl
B) CH₃Cl > CH₃CH₂Cl > (CH₃)₂CHCl > (CH₃)₃CCl
C) (CH₃)₂CHCl > (CH₃)₃CCl > CH₃Cl > CH₃CH₂Cl
D) CH₃CH₂Cl > CH₃Cl > (CH₃)₂CHCl > (CH₃)₃CCl
Answer: A) (CH₃)₃CCl > (CH₃)₂CHCl > CH₃CH₂Cl > CH₃Cl
Explanation:
SN1 reactivity increases with the stability of the carbocation. Tertiary > secondary > primary > methyl.
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