Haloalkanes and Haloarenes Quiz - ICSE Class 12 Chemistry
Free practice quiz: Haloalkanes and Haloarenes (ICSE Class 12 Chemistry). 15 multiple-choice questions with answers and explanations. Play online, no sign-up needed.
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Finkelstein reaction is used for the preparation of:
- Alkyl chlorides from alkyl bromides
- Alkyl iodides from alkyl chlorides
- Alkyl fluorides from alkyl bromides
- Alkyl iodides from alkyl bromides
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Answer: D. Alkyl iodides from alkyl bromides
The Finkelstein reaction is a halogen exchange reaction. It involves the reaction of an alkyl halide with an alkali metal iodide (like NaI or KI) in a polar aprotic solvent like acetone. The low solubility of NaI or KI in acetone drives the equilibrium towards the formation of the alkyl iodide. For example, R-Br + NaI (in acetone) -> R-I + NaBr (precipitates out).
Which of the following compounds is a vicinal dihalide?
- 1,1-dichlorobutane
- 1,2-dichlorobutane
- 1,3-dichlorobutane
- 1,4-dichlorobutane
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Answer: B. 1,2-dichlorobutane
A vicinal dihalide (or vicinal halide) is a compound with two halogen atoms attached to adjacent carbon atoms. In 1,2-dichlorobutane, the chlorine atoms are on the first and second carbon atoms, which are adjacent.
Which haloalkane would give the largest yield of but-1-ene upon dehydrohalogenation with a strong base?
- 1-bromobutane
- 2-bromobutane
- 1,2-dibromobutane
- 2,2-dibromobutane
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Answer: A. 1-bromobutane
To obtain but-1-ene as the major product from dehydrohalogenation, the starting material should be a primary haloalkane with the leaving group on the terminal carbon. 1-bromobutane will undergo E2 elimination to form but-1-ene. 2-bromobutane will primarily form but-2-ene (Zaitsev product). 1,2-dibromobutane and 2,2-dibromobutane are dihalides and would undergo different reactions, potentially leading to alkynes or other products.
The conversion of chlorobenzene to phenol using NaOH requires:
- High temperature and pressure
- Low temperature and pressure
- Room temperature and pressure
- Acidic conditions
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Answer: A. High temperature and pressure
Chlorobenzene is less reactive towards nucleophilic substitution due to the partial double bond character of the C-Cl bond and the electron-rich nature of the benzene ring. Therefore, its conversion to phenol using NaOH requires harsh conditions of high temperature (around 300°C) and high pressure (around 300 atm) in a process known as Dow process. At lower temperatures, benzene is formed, and at even higher temperatures, decomposition can occur.
The reaction of ethyl bromide with magnesium in dry ether followed by carbon dioxide and then hydrolysis yields:
- Propanoic acid
- Ethanoic acid
- Propanol
- Ethanol
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Answer: A. Propanoic acid
Ethyl bromide (CH3CH2Br) reacts with magnesium in dry ether to form ethylmagnesium bromide (CH3CH2MgBr), a Grignard reagent. This Grignard reagent reacts with carbon dioxide (CO2) to form ethylmagnesium carboxylate. Acid hydrolysis of this intermediate yields propanoic acid (CH3CH2COOH).