Which of the following is a meta directing group?
Show Hint
- \( F \)
- \( \text{NHCH}_3 \)
- \( \text{NH}_2 \)
- \( \text{CF}_3 \)
The Correct Option is D
Solution and Explanation
A meta-directing group is an electron-withdrawing group that decreases electron density at the ortho and para positions of a benzene ring, making electrophilic substitution more likely at the meta position. Among the given options, \( \text{CF}_3 \) is a strong electron-withdrawing group due to the high electronegativity of fluorine atoms.
It exerts a -I (inductive withdrawing) effect, pulling electron density away from the benzene ring and making the ortho and para positions less reactive to electrophiles. As a result, substitution occurs at the meta position.
On the other hand: - Fluorine (F) is an electron-withdrawing group by inductive effect (-I) but has a +M (mesomeric donating) effect, making it an ortho/para director.
- Amines (NH\(_2\), NHCH\(_3\)) are strong electron-donating groups due to their +M effect (resonance donation), which increases electron density at the ortho and para positions, making them ortho/para directors.
Since CF\(_3\) is the only strong electron-withdrawing group without a significant resonance donating effect, it is the correct meta-directing group.
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