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Which of the following represents an INCORRECT order for the -I (inductive electron-withdrawing) effect?

1. -F > -Cl > -Br > -I
2. -NR3+ > -NH3+ > -NO2
3. -F > -OH > -NH2
4. Phenyl > -C(triple bond)CH > -H

Correct answer: Phenyl > -C(triple bond)CH > -H

Solution

Halogens follow F > Cl > Br > I; positively charged groups are strongly -I; F > OH > NH2 follows electronegativity. For carbon substituents, the ethynyl group (sp carbon, higher s-character, more electronegative) exerts a stronger -I effect than phenyl, so the order Phenyl > -C(triple)CH is wrong.

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