bzk

Jul 15, 2009
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Hi everyone. I had a question regarding a few activators/deactivators as well as a question concerning basicity.

(1) NHCH3 - Is this an activator? I assume the lone pair on the nitrogen is entering the aromatic ring.

(2) NH3+ - Deactivator? The positive charge withdraws electron density from the aromatic ring. Also, in comparison to other deactivators such as carbonyls, SO3H, nitriles, NO2, is NH3+ the weakest/strongest or in between them?

(3) Of the halides, which is the most deactivating and why?

(4) Basicity Question: Imidazole (2 nitrogens) vs Pyrrolidine (1 nitrogen).

I understand that the nitrogen not bonded to the hydrogen in Imidazole is the most basic due to its lone pair being not tied up in the aromatic system. However, is the nitrogen bonded to the hydrogen in Imidazole or the nitrogen in Pyrrolidine the least basic? And why?

I apologize for all the questions, but I'm really trying to understand these concepts well. Thank you!
 

G1SG2

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Hi everyone. I had a question regarding a few activators/deactivators as well as a question concerning basicity.

(1) NHCH3 - Is this an activator? I assume the lone pair on the nitrogen is entering the aromatic ring.

(2) NH3+ - Deactivator? The positive charge withdraws electron density from the aromatic ring. Also, in comparison to other deactivators such as carbonyls, SO3H, nitriles, NO2, is NH3+ the weakest/strongest or in between them?

(3) Of the halides, which is the most deactivating and why?

(4) Basicity Question: Imidazole (2 nitrogens) vs Pyrrolidine (1 nitrogen).

I understand that the nitrogen not bonded to the hydrogen in Imidazole is the most basic due to its lone pair being not tied up in the aromatic system. However, is the nitrogen bonded to the hydrogen in Imidazole or the nitrogen in Pyrrolidine the least basic? And why?

I apologize for all the questions, but I'm really trying to understand these concepts well. Thank you!
Generally, electron donating groups (EDG) are activators, and electron withdrawing groups (EWG) are deactivators (for electrophilic aromatic substitution). The EDG can be generically represented as G: or G, and the EWG can be generically represented as G=O, or G+.

NHCH3 - Is this an activator? I assume the lone pair on the nitrogen is entering the aromatic ring. Yes (G ).

(2) NH3+ - Deactivator? The positive charge withdraws electron density from the aromatic ring. Also, in comparison to other deactivators such as carbonyls, SO3H, nitriles, NO2, is NH3+ the weakest/strongest or in between them? Yes (G+).

(3) Of the halides, which is the most deactivating and why? Since the halogens have nonbonding electrons that can donate electron density through pi bonding, I would say the most deactivating halide would be fluoride, as it is the most electronegative and would least likely be willing to donate its electrons for resonsance stabilization of the positively charged arenium intermediate.

(4) Basicity Question: Imidazole (2 nitrogens) vs Pyrrolidine (1 nitrogen).
Imidazole is an aromatic compound. Pyrrolidine would be more basic because the electrons on N in imidazole can goof off in the aromatic ring, lowering basicity. The nitrogen bonded to the hydrogen in imizadole is not basic-it's needed inside the ring for aromaticity (to satisfy the Huckle number requirement). The only nitrogen available to act as a base would be the nitrogen with no hydrogen bonded to it.
 
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bzk

Jul 15, 2009
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Actually, it turns out fluoride is the least deactivating with iodide being the most deactivating of the halides (I>Br>Cl>F).

As for the pyrrolidine, are you saying that the nitrogen in it is the most basic of all 3 nitrogens? And the nitrogen bonded to the H in imidazole being the least basic of the 3?

I have another questions regarding synthesis, if you don't mind answering it. How can I synthesis butyl isopropyl sulfide using 1-butanol, 2-propanol, and any solvents/reagents.

Thanks for your help so far - it's been very helpful!
 

G1SG2

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Actually, it turns out fluoride is the least deactivating with iodide being the most deactivating of the halides (I>Br>Cl>F).

As for the pyrrolidine, are you saying that the nitrogen in it is the most basic of all 3 nitrogens? And the nitrogen bonded to the H in imidazole being the least basic of the 3?

I have another questions regarding synthesis, if you don't mind answering it. How can I synthesis butyl isopropyl sulfide using 1-butanol, 2-propanol, and any solvents/reagents.

Thanks for your help so far - it's been very helpful!
Are these homework questions?
 

Hemichordate

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So is a benzene ring/phenyl group considered activating or deactivating? EK wasn't really clear on this one.
 

Charles_Carmichael

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Actually, it turns out fluoride is the least deactivating with iodide being the most deactivating of the halides (I>Br>Cl>F).

As for the pyrrolidine, are you saying that the nitrogen in it is the most basic of all 3 nitrogens? And the nitrogen bonded to the H in imidazole being the least basic of the 3?

I have another questions regarding synthesis, if you don't mind answering it. How can I synthesis butyl isopropyl sulfide using 1-butanol, 2-propanol, and any solvents/reagents.

Thanks for your help so far - it's been very helpful!
Is this because iodide is a larger atom and can spread the electron density around more? Similar to how HI is a stronger acid than HF?
 

thebillsfan

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Is this because iodide is a larger atom and can spread the electron density around more? Similar to how HI is a stronger acid than HF?
thats what i initially thought, but that makes sense if we're talking iodine vs fluorine IONS. these aren't ions, but subtituents on a ring. so...i dont believe whoever said iodine was more deactivating unless they can come up with a reason