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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g3052

Select the correct statement(s) about the allyl cation $CH X_{2} = CH - CH X_{2} X^{+}$ .

AThe pi system contains four electrons.
BAll three carbons are $s p^{2}$ hybridised.
CThe two C-C bonds have equal length.
DThe central carbon carries essentially no positive charge.

Answer: B, C, D

Two equivalent resonance forms place the charge on C1 and C3 alone. The delocalisation makes the two C-C bonds identical and requires three parallel

p

orbitals on three

s p^{2}

carbons. Only two pi electrons are in the system, since the carbocation has an empty

p

orbital.

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