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Give reasons for the following : (i) Phenol is more acidic than methanol. (ii) The C-O-H bond angle in alcohols is slightly less than the tetrahedral angle (109^(@)28.). (iii) (CH)(3))_(2)C-O-CH_(3) on reaction with HI gives (CH_(3))_(3)C-I andCH_(3)-OH as the main products and not (CH_(3))_(3)C-OH and CH_(3)-I. |
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Answer» Solution :(i) Phenol is more acidic than methanol. Phenoxide ion aft er the loss of proton is more stable than methoxide ion after the loss of proton. Therefore phenol is more acidic than methanol.  Thus phenoxide ion gets stabilised DUE to resonance. No such STABILISATION with methoxide ion `(CH_(3)O^(-))` takes place. (ii)  The `C-O-H` bond angle in alcohol is slightly less than the tetrahedral angle `(109^(@)28.)`. This is due to repulsion between the lone pairs of electrons on oxygen. (iii) This is because the deparature of leaving group `(HO-CH_(3))` creates a more stable carbocation `[(CH_(3))_(3)C^(+)]` and the reaction follows a `S_(N)1` mechanism. `CH_(3)-OVERSET(CH_(3))overset("|")underset(CH_(3))underset("|")"C "-underset(H)overset(+)O-CH_(3) overset("Show")rarr CH_(3)-overset(CH_(3))overset("|")underset(CH_(3))underset("|")(C^(+))+CH_(3)OH` `CH_(3)-overset(CH_(3))overset("|")underset(CH_(3))underset(CH_(3))underset("|")(C^(+))+I^(-) overset("Fast")rarr CH_(3)-overset(CH_(3))overset("|")underset(CH_(3))underset("|")"C "-I` |
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