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Explain the structures of alcohols and phenols. |
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Answer» Solution :In ALCOHOLS, the -OH group is bonded to the `sp^(3)` hybridized carbon. The oxygen of the -OH group is also `sp^(3)` hybridized with two lone pair of ELECTRONS. Thus, the carbon-oxygen bond in alcohol is formed by the straight overlapping of `sp^(3)` orbitals of carbon and oxygen. `to`In alcohols, the bond angle is slightly less than the regular tetrahedral angle (`109^(@) 28.`) because of lone-lone pair REPULSIONS on oxygen atom. The bond angle in methanol is `108.9^(@)`. In phenols, the C-O bond length in phenol is smaller than methanol because (i) PARTIAL double bond character on account of conjugation of unshared electron pair of oxygen with the aromatic ring and (ii) The `sp^(2)` hybridized state of carbon to which the oxygen of -OH group is bonded. The bond angle in phenol is `109^(@)`. The -O bond length in methanol is 142 pm and in phenol it is 136 pm.  The dipole moment of phenol (1.54 D) is smaller than methanol (1.71 D) because the C-O bond in phenol is less polar due to electron withdrawing effect of benzene ring while in methanol, the C- bond is more polar due to electron donating effect of methyl group. |
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