Animated Solution for Chemistry - Organic Chemistry: The major product of the following reaction is Conc. ${\text{HNO}}_3$ + conc. ${\text{H}}_2{\text{SO}}_4⟶$

Imagine you are looking at a crowded dance floor, which in our case is a benzene ring. This ring is already populated by three distinct guests: a hydroxyl group ($-\text{OH}$) at the top, a methyl group ($-{\text{CH}}_3$) at the meta position, and a nitro group ($-{\text{NO}}_2$) at the para position. This specific arrangement gives us the starting molecule: 3-methyl-4-nitrophenol.

The reaction conditions provided are concentrated nitric acid (${\text{HNO}}_3$) mixed with concentrated sulfuric acid (${\text{H}}_2{\text{SO}}_4$). This is the classic recipe for an electrophilic aromatic substitution, specifically nitration. The sulfuric acid acts as a catalyst to generate the highly reactive electrophile, the nitronium ion (${\text{NO}}_2^{+}$). The question now is: where will this new guest find a spot on the crowded benzene ring?

To predict the landing spot of the incoming nitronium ion, we must evaluate the influence of the guests already on the ring.

1. The hydroxyl group ($-\text{OH}$) is a powerful activator. Through its $+R$ (resonance) effect, it pumps electron density into the ring, specifically directing incoming electrophiles to the ortho and para positions. 2. The methyl group ($-{\text{CH}}_3$) is a weak activator, directing ortho and para via hyperconjugation ($+H$) and inductive ($+I$) effects. 3. The nitro group ($-{\text{NO}}_2$) is a strong deactivator, pulling electron density away from the ring via its $-R$ effect.

In the battle of directing groups, the strongest activator always wins. Therefore, the $-\text{OH}$ group will dictate the orientation of the incoming ${\text{NO}}_2^{+}$ ion.

The $-\text{OH}$ group wants to direct the new nitro group to its ortho or para positions. However, the para position (position 4) is already occupied by the existing nitro group. This leaves us with two available ortho positions: position 2 and position 6.

Let's look closely at position 2. It is sandwiched directly between the hydroxyl group and the methyl group. If the bulky nitronium ion tries to squeeze in there, it will experience severe steric hindrance (physical crowding).

Conversely, position 6 is relatively open and free from such crowding. It is electronically activated by the $-\text{OH}$ group and sterically accessible.

Because chemistry favors the path of least resistance, the nitronium ion will preferentially attack the sterically favorable position 6.

This results in the formation of 5-methyl-2,4-dinitrophenol (also named 3-methyl-4,6-dinitrophenol depending on numbering priority) as the major product. When we compare this structure to our given choices, it aligns perfectly with option (c).