Electrophillic vs Nucelophillic Aromatic Substitution

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I was curious as to exactly how you guys tell...I've really kind of been guessing

From what I've noticed from questions I've gotten wrong is that an EWG leads to nucleophilic aromatic substitution; and adds on whatever to the Meta position? [unless it's a halogen then Ortho/para]

Does that mean a EDG leads to electrophillic aromatic substitution, but instead of substituting the EDG it just adds ortho/para?

 

[monkeyvokes]

electrophilic aromatic substitution:
electron donating groups preferentially direct ortho/para (para preferred for sterics)
electron withdrawing groups direct meta
draw resonance structures to see where electron density goes and you will see why this occurs

the exception for EAS is the halogens, which direct because of induction and not resonance (the resonance structure would put an unfavorable positive charge on a halogen).

With EAS, you do reactions like halogenation, nitration, sulfonation, etc
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nucleophilic aromatic substitution is not as commonly discussed as EAS is in undergrad organic chem. NAS was not in the Smith organic chemistry textbook, but did appear on the ACS exam (if your university gave that standardized test at the end of organic 2).

NAS takes the form of addition/elimination or elimination/addition and the specifics can be found here: http://www.mhhe.com/physsci/chemist...s/carey04oc/ref/ch23reactionsarylhalides.html

neither of which are listed as being tested for on the mcat, but I did once see an EWG or EDG group question on a practice test..

 

[BerkReviewTeach]

neither of which are listed as being tested for on the mcat...

I am so glad you added this caveat. That was removed from the topic list in 2004

 

[IcemanMD]

I am so glad you added this caveat. That was removed from the topic list in 2004

I was going to say, if BR didn't cover it there's no way it would be on the test.