Answer to Question #24121 in Organic Chemistry for brittney
HO - N+ -O- + H-OSO3H = HO+ - N+ -O- + HSO4-
II & I II
O H & O
HO+ - N+ - O-& =& H2O + O=N+=O
Electrophilic aromatic substitution, in this case nitration, occurs primarily at the 5 -position in 2-hydroxybenzoic acid (salicylic acid, because the hydroxyl functionality at C-2 orients an incoming electrophile (NO2+) to the positions that are orto and para to it. This can be seen by writing out the resonance structures for this compound, which will place formal negative charges at C-1, C-3 and C-5. C-1 is already occupied, so substitution can only occur at C-3 and C-5. The effect of the carboxylic acid group is deactivating at C-2 (which is occupied by the OH), C-4 and C-6, which again allows only substitution at C-3 and C-5. I suspect that C-5 is somewhat more favored over C-3 simply because of steric effects. That is to say that the OH group at C-2 may interfere somewhat with the approach of the nitro group. This steric hindrance does not occur at C-5, since C-4 and C-6 both have small H-atoms attached.
C6H4CO(OH)2 + HNO3 + H2SO4 = NO2-C6H4CO(OH)2
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