JEE Main levelSingle correct optionDifficulty 2 of 3g1175
Which hydrogen of propene, CHX3−CH=CHX2, is abstracted most easily by a free radical such as Br∙?
Aa hydrogen of the terminal =CHX2 group
Ba hydrogen of the CHX3 group (allylic hydrogen)
Cthe hydrogen on the middle carbon, =CHX−
Dall hydrogens are abstracted at the same rate
Answer: B
Removing an allylic hydrogen gives the allyl radical CHX2=CH−CHX2∙, stabilised by resonance. Removing a vinylic hydrogen would give a vinyl radical with no resonance, which is much less stable.