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JEE Advanced levelSingle correct optionDifficulty 3 of 3hc012

An alkane-forming intramolecular Wurtz cyclisation of a dibromoalkane (sodium, dry ether) gives a cycloalkane which on free radical monochlorination gives only one monochloro product (ignore stereoisomers). The dibromoalkane is

  1. A1,3-dibromobutane
  2. B1,3-dibromo-2-methylpropane
  3. C1,4-dibromobutane
  4. D1,4-dibromo-2-methylbutane

Answer: C

1,4-Dibromobutane cyclises to cyclobutane, whose eight hydrogens are equivalent, giving one monochloride. 1,3-Dibromobutane and 1,3-dibromo-2-methylpropane both give methylcyclopropane (3 structural monochlorides). 1,4-Dibromo-2-methylbutane gives methylcyclobutane (4 structural monochlorides).
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