Explain the position of substitution observed in the bromination of thiophene-3-carboxylic acid shown in Eq. 26.18. Draw the arenium ion intermediates for all possible positions of substitution and show that the intermediate in the observed substitution is the most stable one.

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CO₂H Br₂ CH,CO,H 3-thiophenecarboxylic acid Br CO₂H 5-bromo-3-thiophenecarboxylic acid (69% yield) (26.18)