1.

(a) Discuss the structural relationship of water , alcohol and ethers. (b) Compare the bond angles of H-O-H,C-O-H fo alcohol and C-O-C of ethers. (c ) What is crown ether ? How is it named ? 9d) What is absoluteether ? (e ) Compare the following alkyl halides in decreasingorder of reactivity in the Williamson's reaction : ClCH_(2)CH_(2)CH_(3)(A),""BrCH_(2)CH_(2)CH_(3)(B), (CH_(3))_(3)C C H_(2)Br(C ),""ClCH_(2)CH=CH_(2)(D) (f) Give six types of ethers and cannot be synthesised by the typical Williamson's reaction.

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Solution :[Hint]
(i) Alcohols and ethers may be regarded as derivatives of H-O-H . The replacement of one H atom affords alcohols, ROH. In ethers both hydrogen atoms are replaced.
(ii) In all the three cases, oxygen undergoes `sp^(3)` -hybridization, there is contraction in the bond angle , which is `105^(@)`. The bond angle is very close to `109^(@)`in alcohols. The C-O-C bond angle in ethers is about `110^(@)` on account of repulsive van der Waals' forces between groups of larger size.
(iii)The heterocyclic polyether is called crown ether. It is named on the basis of total number of atoms in the ring and number of oxygen atoms. [15] crown -5 MEANS 15 atoms inthe ring including 5 oxygen atoms.
(iv) Absolute ether means diethyl ether absolutely free from water.
(V) `underset(("Allylic"))(D) gtunderset(("Bromide"))(B)gtunderset(("Chloride"))(A)gtunderset(("NEOPENTYL"))(C)`
(vi)(i) `R_(3)C-O-CR_(3)`(Both c atoms are `3^(@))`
(ii) `R_(2)CH-O-CHR_(2)`(Both C atoms are `2^(@))`
(iii) `R_(3)C-O-CHR_(2)`(One C is `3^(@)` and one is `2^(@))`
(iv) `Ar-O-Ar `(Both are aryl groups )
(v) `RCH=CH-O-CH=CHR'` (Both are vinyl groups )
(vi) `R_(3)C C H_(2)-O-CH_(2)CR_(3)` ( Both are neopentyl groups )
(vii) `RCH=CH_(2)+R'OHunderset((ii)NaBH_(4))OVERSET((i)Hg(OOC CF_(3))_(2))(rarr)Runderset(OR')underset(|)(C)H -underset(H)underset(|)(C)H_(2)`


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