In the given chemical reaction

The mixture of three compounds A, B and C is formed respectively in what ratio?

51%, 47%, 2%

The correct answer is option 3.51%, 47%, 2%.

Direct nitration of aniline yields tarry oxidation products in addition to the nitro derivatives. Moreover, in the strongly acidic medium, aniline is protonated to form the anilinium ion which is meta directing. That is why besides the ortho and para derivatives, significant amount of meta derivative is also formed.

In the case of nitration of aniline intermediate stability determines products.The following figure depicts possible electrophillic attack on aniline. Structures 4 and 12 are additional stable resonance structures obtained by attack of nitronium electrophile at ortho and para positions.

Structure 8 is relatively unstable due to negative effect of Nitrogen.

In nitration of aniline in strong acid \((HNO_3, H_2SO_4)\) aniline changes to anillium ion. Anillium withdraws electron density. Its effect is felt maximum at ortho followed by meta and then para position. Consequently, very little of ortho nitrated product is formed.

Since electron withdrawing inductive effects are minimum at para position, maximum nitration occurs here.

Summarizing,

Even though there exists a possibility of hydrogen bonding in ortho nitro aniline, strong deactivating influence of \(NH_3^+\) on benzene ensures least electron density at ortho position in aniline leading to only \(2\%\) of ortho nitro aniline.

Such electron withdrawing tendencies of \(NH_3^+\) are minimum at para position in aniline therefore \(51\%\) of para nitro aniline is formed.