Same chapter3 marksDifficulty: Medium
Why is benzene unusually stable and why does it prefer substitution to addition?
Hydrocarbons
3 marksDifficulty: Medium
Why do alkanes undergo substitution while alkenes undergo addition?
Original Khojo Papers practice question — not from a past board paper.
Answer
An alkane is saturated: all its bonds are strong sigma bonds and there is no site of electron density to attract a reagent, so it can only have one atom replaced by another. An alkene has a pi bond whose electrons are loosely held and exposed, which attracts electrophiles and lets a reagent add across the double bond to give a more stable saturated product.
No citable source has been recorded for this record. Treat it as practice material, not as fact.
Explanation
This is why bromine water distinguishes the two.
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