Question

(a) Indicate whether the following are `S_(N^(1)),S_(N^(2)),E_(1) " or "E_(2)` reactions.
`(i) CH_(3)CH_(2)CH_(2)CI+I^(-) to`
`(ii) (CH_(3))_(3) CBr+CN^(-)(alc.) to`
`(iii) CH_(3)CH(Br)CH_(3) +OH^(-) (alc.) to`
`(iv) (CH_(3))_(3) C-Br+H_(2)O to`
(b) Give the decreasing order of reactivity of the alkaline hydrolysis of the following alkyl halides toward `(A)S_(N^(1))(B) S_(N^(2))(C)` in pressure of `AgNO_(3).`
`(i) (CH_(3))_(2)C(Br) -C_(2)H_(5) (ii)C_(5)H_(11)Br`
`(iii) C_(2)H_(5)CH(Br)C_(2)H_(5)`
(c) Give the decreasing order reactivity of the alkaline hydrolysis of hte following halides towards `S_(N^(1)) (i) MeCI (ii) PhCH_(2)CI(ii)Ph_(2)CHCI(iii)Ph_(3)C-CI`.
(d) Determine the relative `S_(N^(2))` reactivity with NaCI in aprotic DMSO of the following alkyl halides :
`(A) (i) CH_(3)CHCICH_(2)CH_(3)(ii)CH_(3)CHBrCH_(2)CH_(3)`
`(iii) CH_(3)CHICH_(2)CH_(3)`
`(B) (i) CH_(3)CH(CH_(3))CH_(2)CH_(2)I`
`(ii) CH_(3)CH(CH_(3))CHICH_(3)(iii) CH_(3)CI(CH_(3)) CH_(2)CH_(3)`
(e) Arrange the following in the order of decreasing nucleophilic character:
`H_(2)O,^(-)OH,CH_(3)O^(-), CH_(3)COO^(-)`
(f) Arrange the following in the decreasing order as leaving group in `S_(N)` reaction:
`CH_(3)COO^(-), C_(6)H_(5)O^(-), C_(6)H_(5)SO_(3)^(-), CH_(3)O^(-)`

Answer 1

`(a) (i) CH_(3)CH_(2)CH_(2)-I " is " S_(N^(2)) " reaction "(1^(@)"halide and " I^(-)` is a good nucleophile and poor base.
`(ii) CH_(3)CH=CH_(2) " is " E_(2)` reaction, less polar solvent favours `E_(2)`.
`(iv) (CH_(3))_(3)C-OH " is "S_(N^(1))` reaction as `H_(2)O` is not basic enough to remove a proton to give elimination reaction.
`(b) (A) (i) gt (iii) (3^(@) gt 2^(@) gt 1^(@)" alkyl halides ")S_(N^(1))`.
`(B) (ii) gt (iii) gt (i) (1^(@) gt 2^(@) gt 3^(@) " alkyl halides")S_(N^(2)).`
`(C) (i) gt (iii) gt (ii) : " Heavy ions such as " Ag^(+) " or " Pb^(2+) " catalyse " S_(N^(1))`.
`(C) (iv) Ph_(3) C-CI gt (iii) Ph_(2) CH-CI gt (ii) PhCH_(2) -CI gt (i) NeCI.`
`(d) (A) (iii) gt (ii) gt (i) ("Group leaving ability is " I^(-) gt Br^(-) gt CI^(-))`
`(B) (i) gt (ii) gt (iii) ("steric factor makes the reactivity " 1^(@) gt 2^(@) gt 3^(@))`.
(e) When the nucleophilic centre is same . The nucleophilicity is same as basic character.
Acidic character :`H_(3)O^(+) gt CH_(3)COOH gt CH_(3)OH gt H_(2)O.`
Basicity and nucleophilicity : `H_(2)O lt CH_(3)COO^(-) lt CH_(3)O^(-) lt OH^(-)`.
(f) Weaker the base or stronger the acid, better is the leaving group.
Acidic character : `C_(6) H_(5)SO_(3)H gt CH_(3)COOH gt C_(6)H_(5)OH gt CH_(3) OH.`