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JEE Main levelOne or more correct optionsDifficulty 2 of 3pl256

A short fragment of a hydrocarbon rubber chain (two repeat units, end groups shown) is drawn. Select all correct statements about its vulcanisation with sulfur.

  1. ASulfur crosslinks form mainly at the allylic positions next to C=C
  2. BA small percentage of sulfur increases strength and elastic recovery
  3. CThe fragment shown has no allylic hydrogens
  4. DCrosslinking occurs only at the vinylic C-H bonds

Answer: A, B

The fragment is cis-1,4-polybutadiene. During vulcanisation sulfur forms S-S bridges at the reactive allylic carbons next to the C=C, which links chains and raises strength and elastic recovery. The fragment has many allylic CH2 groups, so C is wrong, and the crosslinks are not formed only at vinylic C-H bonds, so D is wrong.
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