why Allyl carbocation is more stable than vinyl carbocation

In general, any adjacent lone pair or π bond can also be involved
in resonance delocalization of a carbocation positive charge. Allylic and benzylic
carbocations enjoy resonance stabilization by delocalization of the positive charge to the
adjacent π bond(s). Vinylic and aryl carbocations do not enjoy resonance stabilization
because their π electron clouds are perpendicular to the vacant p orbital of the
carbocation. (Recall that resonance requires the interacting orbitals to be parallel so they
can overlap. Without overlap there can be no resonance.)

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