Question 11: Nomenclature
What is the IUPAC name for CH₃-CH₂-CBr₂-CH₃?
A) 2,3-Dibromobutane
B) 2,2-Dibromobutane
C) 3,3-Dibromobutane
D) 1,2-Dibromobutane
Answer: B) 2,2-Dibromobutane
Explanation:
Identify the longest carbon chain and assign numbers to substituents to give them the lowest possible numbers. Both bromine atoms are attached to the second carbon, so the correct name is 2,2-Dibromobutane.
Question 12: Physical Properties
Which haloalkane is expected to have the lowest solubility in water?
A) CH₃Br
B) C₂H₅Br
C) C₃H₇Br
D) (CH₃)₃CBr
Answer: D) (CH₃)₃CBr
Explanation:
As the carbon chain length increases, solubility in water decreases due to increased hydrophobic character. (CH₃)₃CBr (tert-Butyl bromide) has the largest alkyl group, making it the least soluble in water.
Question 13: Reactions – Nucleophilic Substitution
Which haloalkane will react fastest in an SN2 reaction?
A) CH₃Cl
B) CH₃CH₂Cl
C) (CH₃)₂CHCl
D) (CH₃)₃CCl
Answer: A) CH₃Cl
Explanation:
SN2 reactions are favored by primary haloalkanes due to less steric hindrance. CH₃Cl is a methyl chloride, making it the most reactive in SN2 among the options.
Question 14: Reactions – Halogen Exchange
What is the product when 1-chloropropane is treated with excess NaI in acetone?
A) 1-Iodopropane
B) 2-Iodopropane
C) Propanol
D) No reaction
Answer: A) 1-Iodopropane
Explanation:
This is a Finkelstein reaction, where chloride is replaced by iodide. 1-Chloropropane reacts with NaI in acetone to form 1-Iodopropane and NaCl, which precipitates out.
Question 15: Properties – Reactivity
Which haloalkane is most susceptible to elimination (E2) reaction?
A) CH₃Cl
B) CH₃CH₂Cl
C) (CH₃)₂CHCl
D) (CH₃)₃CCl
Answer: D) (CH₃)₃CCl
Explanation:
Tertiary haloalkanes like (CH₃)₃CCl are highly susceptible to E2 elimination due to the stability of the resulting tertiary alkene and the steric hindrance that disfavors SN2 reactions.
Question 16: Nomenclature – Haloarenes
What is the IUPAC name for o-dichlorobenzene?
A) 1,2-Dichlorobenzene
B) 1,3-Dichlorobenzene
C) 1,4-Dichlorobenzene
D) 2,3-Dichlorobenzene
Answer: A) 1,2-Dichlorobenzene
Explanation:
In ortho (o-) substitution, the substituents are adjacent, occupying positions 1 and 2. Hence, the IUPAC name is 1,2-Dichlorobenzene.
Question 17: Reactions – Haloarenes
Which of the following is a common method to prepare chlorobenzene?
A) Chlorination of benzene using Cl₂ and FeCl₃
B) Nitration of benzene followed by reduction
C) Friedel-Crafts alkylation of benzene
D) Hydrogenation of benzoyl chloride
Answer: A) Chlorination of benzene using Cl₂ and FeCl₃
Explanation:
Chlorobenzene is commonly prepared by the chlorination of benzene in the presence of a Lewis acid catalyst like FeCl₃.
Question 18: Physical Properties – Boiling Point
Which of the following haloalkanes has the highest boiling point?
A) CH₃CH₂Cl
B) CH₃CHClCH₃
C) (CH₃)₂CHCl
D) (CH₃)₃CCl
Answer: A) CH₃CH₂Cl
Explanation:
Boiling points increase with molecular weight and polarity. CH₃CH₂Cl has hydrogen bonding capabilities and less branching compared to other options, resulting in a higher boiling point.
Question 19: Nomenclature – Substituted Haloarenes
What is the IUPAC name for 4-bromo-1-chlorobenzene?
A) 1-Bromo-4-chlorobenzene
B) 4-Bromo-1-chlorobenzene
C) 2-Bromo-1-chlorobenzene
D) 3-Bromo-1-chlorobenzene
Answer: B) 4-Bromo-1-chlorobenzene
Explanation:
Numbering starts to give the substituents the lowest possible numbers. In this case, 1-chloro and 4-bromo are the correct positions, so the name is 4-Bromo-1-chlorobenzene.
Question 20: Reactions – Hydrolysis
What is the product when 1-bromobutane undergoes hydrolysis?
A) Butan-1-ol
B) Butan-2-ol
C) Butanal
D) Butanoic acid
Answer: A) Butan-1-ol
Explanation:
Hydrolysis of 1-bromobutane (a primary haloalkane) with aqueous NaOH leads to substitution, forming butan-1-ol via an SN2 mechanism.
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