There are two step-up methods : (i) Grignard reagent and (ii) nitrile method, for the preparation of carboxylic acids from `RX`, Which method is suitable for the preparation of step-up carboxylic acid from the following `RX` ? Why ? Give the name of the acid also.
(I)
(II)
(III)
(IV) `PhCI`
(V)
(VI)
(VII)
(VIII)
(IX) .

Explanation

(I) Both the methods :
a Grignard reagent (or carbonation) is better as `(I)` is a `2^@` halide, with `overset (Ө) C N. F2` reaction can also occur to give alkene.
(II) By both methods :

As `(II)` is a `1^@ RX`, both the methods are good.
(III) By `G.R` method only :

As `(III)` is a `3^@` , only `G.R` method is suitable, `3^@ RX` does not undergo `SN^2` reaction with `overset (Ө) C N`.
(V) By both methods :

`G.R` method is better , `overset (Ө) C N` could initiate some `E2` reaction to give a stable conjugate alkene.

(VI) Neither method is suitable, as `(IV)` is a `3^@ RX`, which does not react with `overset (Ө) C N`.
The presence of acidic `(OH)` group prevents the formation of `G.R`.

Hence, carboxylic acid can be prepared by first protecting the `(OH)` group by silylation and then perfoming carbonation by `G.R`.

(VII) By `G.R` method only :

`(VII)` is a vinyl halide which does not undergo `SN^2` reaction with `overset (Ө) C N`.
Organometallic compounds of vinyl halides are best prepared by lithium compounds in ether.
(VIII) By nitrile method only :
(succinic acid or butane-1,4-dioic acid) with `Mg (VIII)` woud lead to loss of vivinal `Br` atoms to give alkene and `MgBr_2`.

(IX) By both methods :

`G.R` method is better because `2^@ RX` with `overset (Ө) C N` would undergo `E2` reaction to give the same alkene. Moreover, `overset (Ө) C N` reaction undergoes with inversion to give cis-carboxylic acid.