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Solutions for Reactions of Aromatic Compounds HC CH2 HC CH E H CH2 H E HC HC CH2 C HC E H CH2 HC CH2 H E 6 For ortho and para attack, the positive charge in the sigma complex can be shared by resonance with the vinyl group. This cannot happen with meta attack because the positive charge is never adjacent to the vinyl group. (Ortho attack is shown; para attack gives an intermediate with positive charge on the same carbons.) E "extra" resonance form Br OCH2CH3 OCH2CH3 CH Br H Br Br FeBr3 H Br HC OCH2CH3 C OCH2CH3 Br H H Br OCH2CH3 Br OCH2CH3 7 Attack at only ortho and para positions (not meta) places the positive charge on the carbon with the ethoxy group, where the ethoxy group can stabilize the positive charge by resonance donation of a lone pair of electrons. (Ortho attack is shown; para attack gives a similar intermediate.) (Unshared electron pairs on halogen not shown here.) "extra" resonance form NH2 CH Br H H Br HC NH2 C NH2 Br H H Br NH2 ortho "extra" resonance form 8 NH2 HC Br H H Br CH NH2 HBr C NH2 NH2 HC Br H NH2 Br H H Br C H NH2 NH2 CH Br H meta "extra" resonance form para 387