The mechanism for the nitration is that of electrophilic aromatic substitution. The nitronium ion is directed to the positions ortho and para to the acetamido (-NHCOCH ) group. This occurs because the resonance 3 electron-releasing effect of that group increases the electron density at those positions, helping to stabilize the intermediates that are formed. Substitution para to the acetamido group is favour red over substitution ortho to that group, because the great bulk of the acetamido group shields the ortho positions from approach by reagents. This steric hindrance makes ortho substitution much less likely than para substitution, in which the bulk of the acetamido group has no influence. The ortho substitution product is formed in small quantities in this reaction.