Account for the following (i) t-butyl chloride reacts with aqueous KOH by S_(N^1) mechanism while n-butyl chloride reacts with S_(N^2)mechanism. (ii) p-dichlorobenzene has higher melting point than those of o-and m - dichlorobenzene.

Account for the following (i) t-butyl chloride reacts with aqueous KOH

1.	Account for the following (i) t-butyl chloride reacts with aqueous KOH by S_(N^1) mechanism while n-butyl chloride reacts with S_(N^2)mechanism. (ii) p-dichlorobenzene has higher melting point than those of o-and m - dichlorobenzene.
Answer» Solution :(i) In t-butyl chloride, there is more STERIC hindr ance and it involves formation of a stable tertiary CARBOCATION. Therefore it reacts with KOH by`S_(N^1)`- mechanism rather than `S_(N^2)`-mechanism because `S_(N^1)`-mechanism is favourable in case of steric crowding and is directly proportional to partial positive charge on carbon atom. In n-butyl chloride, there is least steric hindrance and involves formation of less stable primary carbocation. Thus it takes place in one step and is favoured by `S_(N^2)`-mechanism. (ii) Melting point ofp- dichlorobenzene is HIGHER than that of ortho and meta-dichlorobenzene. This is due to the FACT that is has a symmetrical structure and therefore, its molecules can easily pack closely in the crystal lattice. p-dichlorobenzene being more symmetrical fits closely in the crystal lattice and has stronger intermolecular ATTRACTION than o & m isomers. So p-isomer has high melting point than the corresponding o & m-isomers.