HydrocarbonsMedium
Question
In the presence of preoxide, hydrogen chloride and hydrogen iodide do not give anti- Markownikoff,s addition to alkenes because :
Options
A.both are highly ionic
B.one is oxidising and the other is reducing
C.one of the steps is endothermic in both the cases
D.all the steps are exothermic in both the cases
Solution
Addition of H - X in presence of peroxide is supposed to be a free radical addition. Because addition reactionas are accompanied with secrease in entropy and so they are spontaneous only when ᐃH is highly negative .In the addition of H - Cl step
ClCH2 - •CH2 + H - Cl → ClCH2•CH3 + Cl• is endothermic while in the addition of HI, step I• + CH2 = CH2 → ICH2 - •CH2 is endotherimic. In the addition of HBr, both the steps are exothermic. Thus HBr adds by free radical mechanism spontaneously while H - Cl and H - I do not, as their ᐃH is not sufficiently negative.
(i) Assertion and reason both are correct and reason is the correct explanation of the assertion .
(ii) Assertion is correct but reason is not correct explanation of the assertion . (addition of Br2) to trans-butene-2 is ionic while it is electrophilic addition in alkene.)
ClCH2 - •CH2 + H - Cl → ClCH2•CH3 + Cl• is endothermic while in the addition of HI, step I• + CH2 = CH2 → ICH2 - •CH2 is endotherimic. In the addition of HBr, both the steps are exothermic. Thus HBr adds by free radical mechanism spontaneously while H - Cl and H - I do not, as their ᐃH is not sufficiently negative.
(i) Assertion and reason both are correct and reason is the correct explanation of the assertion .
(ii) Assertion is correct but reason is not correct explanation of the assertion . (addition of Br2) to trans-butene-2 is ionic while it is electrophilic addition in alkene.)
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