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This point (iv) has been given under reasons for extremely low reactivity of aryl and vinyl halides. I cannot understand it. First of all, isn't the positive carbon atom in phenyl as well as vinyl carbocation sp-hybridized. But in the point, the positively charged carbon atom of the phenyl carbocation is referred to as sp2-hybridized. I cannot understand why. Also I cannot understand the "perpendicular part". That the orbitals are perpendicular and so the carbocation is not formed. But how are they perpendicular and how does this hinder the formation of carbocation. I cannot understand the last diagram (for vinyl carbocation). Please help.