Arrange the following compounds in increasing order of `S_(N)1` reactivity.
`(i) ClCH_(2)CH = CHCH_(2)CH_(3)`,
`CH_(3)C(Cl) = CHCH_(2)CH_(3)`,
`CH_(3)CH = CHCH_(2)CH_(2)Cl `,
`CH_(3)CH = CHCH(Cl)CH_(3)`
(ii) `CH_(3)CH_(2)Br, CH_(2) = CHCH(Br)CH_(3)`,
`CH_(2) = CHBr, CH_(3)CH(Br)CH_(3)`
(iii) `(CH_(3))_(3)C Cl , C_(6)H_(5)C(CH_(3))_(2)Cl `,
`(CH_(3))_(2)CHCl , CH_(3)CH_(2)CH_(2)Cl `

Explanation

The reactivity for Spi reactivity follows the order :
`(i) CH_(3) - underset(I)underset(Cl)underset(|)C = CH - CH_(2) - CH_(3) lt CH_(3) - CH = underset(II) (CH - CH_(2) - CH_(2)Cl) lt ClCH_(2) - CH = underset(III) CH - CH_(2) - CH_(3) lt CH_(3) - CH = CH - underset(IV)underset(Cl)underset(|)CH - CH_(3) `
IV shows maximum reactivity because the carbocation is stabilised by resonance (conjugation from double bond). I is least reactive because the carbocation is least stable, being linked to double bond directly.
(ii) `CH_(2) = CHBr lt CH_(3)CH_(2)Br lt CH_(3) - underset(Br)underset(|)CH - CH_(3) lt CH_(3) = CH - underset(Br)underset(|)CH - CH_(3) `
This is again based upon the stability of the carbocation .
(iii) `CH_(3)CH_(2)CH_(2)Cl lt (CH_(3))_(2)Cl lt (CH_(3))_(2)CHCl lt (CH_(3))_(3) C Cl lt C_(6)H_(5) - underset(CH_(3))underset(|)overset(Cl)overset(|)C - CH_(3)`
The carbocation from `C_(6)H_(5)C(CH_(3))_(2)Cl ` is stabilised to the maximum extent.