Assertion (A): the two C-C bonds in the allyl cation CH2=CH-CH2+ have equal length. Reason (R): the allyl cation has four electrons in its three-centre pi system.

A is true, R is false, and A is explained by delocalisation over the three carbons

Both A and R are true and R explains A

A is true, R is false, and A is explained by delocalisation over the three carbons

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JEE Advanced levelSingle correct optionDifficulty 3 of 3g3036

Assertion (A): the two C-C bonds in the allyl cation $CH X_{2} = CH - CH X_{2} X^{+}$ have equal length. Reason (R): the allyl cation has four electrons in its three-centre pi system.

ABoth A and R are true and R explains A
BA is false and R is true
CA is true, R is false, and A is explained by delocalisation over the three carbons
DBoth A and R are false

Answer: C

Resonance between the two equivalent structures makes both C-C bonds identical, with a bond order of 1.5, so A is true. The pi system of the allyl cation has only two electrons (one pi bond, one empty

p

orbital) in three centres, so R is false.

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Assertion (A): the two C-C bonds in the allyl cation CHX2​=CH−CHX2​X+ have equal length. Reason (R): the allyl cation has four electrons in its three-centre pi system.

Answer: C

More questions on Carbocations: formation, stability, rearrangements

Assertion (A): the two C-C bonds in the allyl cation $CH X_{2} = CH - CH X_{2} X^{+}$ have equal length. Reason (R): the allyl cation has four electrons in its three-centre pi system.