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& ORTHO & PARA DIRECTING GROUPS,META DIRECTING GROUPS

2007-10-22 14:31:24 · 2 answers · asked by Anonymous in Science & Mathematics Chemistry

2 answers

Most organic chemistry texts are pretty clear on this, but here's a nice, neat table:

http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch12/ch12-8b.html

2007-10-22 14:41:23 · answer #1 · answered by Anonymous · 0 0

CH3 is an ortho-para directing group. It donates electrons to the benzene ring. If an electrophile like NO2+ attacks, the ring is reactive because of the extra electron density. Also, if the NO2+ comes into an ortho or para position, resonance spreads the (+) to two other carbons in the ring and the CH3 group. This spreading stabilizes the intermediate, which thus has a good chance to go on to product.

NO2 is meta directing. Actually, it is not meta directing. Rather meta products form as the least of evils. NO2 is electron-withdrawing. This means that the ring is less reactive because of depleted electron density. If NO2+ attacks ortho or para, the (+) of the intermediate is destabilized. This means that it goes into a meta position by default.

An intermediate both-ways substituent is Cl. It is electron-donating by resonance, so it is ortho-para directing. The high electronegativity withdraws electrons by induction, however, so the ring is less reactive than benzene itself.

2007-10-22 14:43:27 · answer #2 · answered by steve_geo1 7 · 0 0

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