Orgo Question
Started by flyingforever
Br is a better leaving group in a SN reaction, yes. But this isn't an SN reaction, its a Nucleophilic Aromatic Substitution reaction
Therefore, the most electronegative atom attracts electrons greater than other atoms down the column.. and leaves first
F > Cl > Br > I
Therefore, the most electronegative atom attracts electrons greater than other atoms down the column.. and leaves first
F > Cl > Br > I
]
I got the first part of this reaction. I don't understand why Br is substituted for NH2. Isn't Br better leaving group than Cl?
In Nucleophilic Aromatic substitution
EWG (NO2) = Ortho/para director
EDG (including Halogen) = Meta director
NH2 is the nucleophile that will substitute the Leaving Group (Br).
NO2 activates the ring at ortho/para. Br is in the para position so it is substituted.
NO2 wouldn't do anything with Cl. Cl is in Meta position.
Last edited:
Advertisement - Members don't see this ad
I think there are specific details that are incorrect in this logic.
NO2 = EWG (deactivating, not activating) = meta director
In Electrophilic Aromatic Substitution <--------
EDG = Ortho/para director
EWG (NO2) Meta director <------
In Nucleophilic Aromatic substitution <--------
EWG (NO2) = Ortho/para director <--------
EDG (including Halogen) = Meta director
Can someone please show the mechanism of the second step in this reaction. All I know about the NaNH2 is that its a strong base and from reviewing the Organic Chemistry section of DAT Destroyer, I know that it there are two halides on an alkane, NaNH2 will take the halides and form an alkyne.
I am on the right track?
I am on the right track?
Part 2 is Nucleophilic Aromatic substitution not Electrophilic Aromatic Substitution.
In Nucleophilic Aromatic substitution <--------
EWG (NO2) = Ortho/para director <--------
EDG (including Halogen) = Meta director
Electrophilic Aromatic Substitution <--------
EDG = Ortho/para director
EWG (NO2) Meta director <------
According to L.G. Wade Organic Chemistry Textbook:
Electrophilic Aromatic Substitution <--------
EDG = Ortho/para director
EWG (NO2) Meta director <------
In Nucleophilic Aromatic substitution <--------
EWG (NO2) = Ortho/para director <--------
EDG (including Halogen) = Meta director
Part 1 is Electrophilic Aromatic Substitution, Br (Halogen) is a deactivating ortho/para director that directs the substitution of H with Cl.
Part 2 is Nucleophilic Aromatic substitution not Electrophilic Aromatic Substitution.
NH2 is the nucleophile that will substitute the Leaving Group (Br).
NO2 activates the ring at ortho/para. Br is in the para position so it is substituted.
NO2 wouldn't do anything with Cl. Cl is in Meta position.
Last edited:
Oh that's right! I didn't notice this was nucleophilic rather than electrophilic. My apologies!
Ibraiz, a Strong base deprotonate a H next to LG, LG leaves and a benzyne is formed. a nucleophile (could be the same strong base) attacks one end of the benzyne to form 1 product or it can attack the other end of benzyne to form a 2nd product.
But most importantly, for Nucleophilic aromatic substitution we need these conditions:
Nucleophilic Aromatic Substition
EWG (NO2) = Ortho/para director
EDG (including Halogen) = Meta director
In Addition-Elimination (1 major product)
Requires a Strong EWG (NO2) on aromatic ring. LG must be in Ortho or para.
If LG at Meta Position, NO RXN! It won't go Addition-Elimination but we can force it to go Elimination-Addition if we use HEAT.
In Elimination-Addition (3 possible products)
Without EWG on aromatic ring to activate benzene we must use
STRONG BASE + HEAT.
We can get Meta & Para mixture product. It is also possible to get ORTHO, META & PARA product, depending on the molecule you start with.
Last edited:
Advertisement - Members don't see this ad
So if there is no other nucleophile beside the strong base it self in the Nucleophilic Aromatic Substitution reaction, then strong base always acts as a nucleophile (replacing the leaving group)?
Does Nucleophilic Aromatic Substitution every stop at benzyne and not do the substitution? I guess it won't be called substitution then it would be elimination but is it possible to have an elimination product rather than a substitution product?
Does Nucleophilic Aromatic Substitution every stop at benzyne and not do the substitution? I guess it won't be called substitution then it would be elimination but is it possible to have an elimination product rather than a substitution product?
I can't even find nucleophilic aromatic substitution in my two college organic books that I have haha, this is odd..
anytime. Nucleophilic aromatic substitution is not that important. It's a topic that was only briefly covered as the last topic of my ochem class.
I think electrophilic aromatic substitution is more important. concentrate on this instead. 🙂
