Question

I've learnt that the OH

group is 2- and 4-directing, but this has caused some confusion. If HNO3
reacts with phenol, would there be any 2,6-dinitrophenol produced?

I know that the first nitro group will add to position 4 or 2, but if one is added to 2, can a second add to 6? Or must position 4 be added prior to 6?

Answer 1

In the nitration of phenol, if the first nitro group adds at the ortho position (2-position), the resulting 2-nitrophenol has the para position (4-position) activated, making 2,4-dinitrophenol the major product. The 6-position would not be directly nitrated after initial ortho substitution.

Step-by-step explanation:

When phenol (ArOH) reacts with nitric acid (HNO3), the OH group is an activating, ortho-para directing group. If nitration occurs and the first nitro (NO2) group adds to the 2-position (ortho to the OH group), the remaining positions 3 and 5 (meta) are deactivated while the 4 (para) and 6 positions remain activated because they are equivalent due to the symmetry of the molecule. In this scenario, there would not be the direct formation of 2,6-dinitrophenol because after the initial nitration at the 2-position, the 6-position becomes deactivated for further nitration.

The second nitration would typically occur at the 4-position since it's activated and also provides more stability due to resonance structures. Therefore, 2,4-dinitrophenol would be expected as the major product prior to any substitution occurring at the 6-position.