NO2 is more electronegative then Florine?

[Lacipart]

A highly electron withdrawing functional group with increase the acidity of a proton...

So, N02 has a higher electron withdrawing affect due to electronegativity? I didn't think 2 x Oxegen was > a Florine if they were split across a atom like that

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[RogueUnicorn]

NO2 can have resonance distribution? NO2 is also very electron withdrawing (refer to its effects on aromatic substitution reactions) due to a partial positive charge on Nitrogen, which is itself a very electronegative atom.

 

[docelh]

Three highly electronegative atoms versus one.

I think the law of addition wins on this one.

 

[MegaSpectacular]

Three highly electronegative atoms versus one.

I think the law of addition wins on this one.

not exactly how things work.

 

[loveoforganic]

It certainly is to an extent. See, monofluoroacetic acid vs trichloroacetic acid pKa.

 

[puravida85]

If we really wanted to see what was going on:

I imagine you can get some benzene, use AlF3 + F2 to attach it to the benzene, than use NO2/H2So4 to attach to another benzene. Run your NMR, evaluate the carbon attached to F and NO2. Or you can attach an acid group to it, and run an acid base test.. Anyhow i'm getting out of control here.

Otherwise,

I think it helps to draw it out, when putting the NO2 on say a benzene ring, you'll notice that N has a positive charge and also an oxygen with a negative charge. I imagine having a strongly electronegative oxygen pulling the electron coverage from N so much that it has lost an electron is pretty serious business. N is in dire need of electrons. Therefore any electrons in it's vicinity will be greatly attracted to it. Fluorine has a electronegative value of 3.98 and O has an EN of 3.44 and N is 3.04. So there are two O's and than an N with a + charge!

 

[MegaSpectacular]

It certainly is to an extent. See, monofluoroacetic acid vs trichloroacetic acid pKa.

yeah. I guess a single example makes a rule for all of ochem...

I just don't like when people over generalize a concept trying to simplify it at the expense of being wrong.

By the way:

Strongly deactivating EWG:

---CN

Moderately deactivating EWG:

---COOH

I'm not too good with math though, what has more additive EN? N or OOH

 

[loveoforganic]

And the technically correct answer for all of o chem is "the math works out that way." is that helpful to someone trying to learn? Electronegativities of proximal substituents do constructively add to an extent, although there are other things to consider.

 

[MegaSpectacular]

And the technically correct answer for all of o chem is "the math works out that way." is that helpful to someone trying to learn? Electronegativities of proximal substituents do constructively add to an extent, although there are other things to consider.

I like Eisenstein's quote:

"Make things as simple as possible, but not simpler."

Saying it is additive is trying to make it simpler than it is. The example I gave is very common and does in no way apply to that rule.

More common groups that don't apply to the "additive" rule...
Strongly Deactivating

--NH3

--NR3

Moderately Deactivating

--COOH

--COOR

 

[RogueUnicorn]

guys... seriously. i think i covered the big picture reasons already. add relevant info..

 

[MegaSpectacular]

In fact, it is even confusing to someone who doesn't understand the concepts...

as

NR2
NH2

are weaker EWG than...

NR3
NH3

wait. They aren't weaker EWG, they are EDG. Telling someone you just add EN to figure out how strong an EWG is dumbing down a concept. That is all I was saying, and it is true. As someone may predict that NR2 and NH2 are just weaker EWGs.

 

[MegaSpectacular]

guys... seriously. i think i covered the big picture reasons already. add relevant info..

I originally added relevant info.

I commented on how an "additive" rule doesn't make sense.

Then it was challenged, so I defended it. And yet again it was challenged.

I'm done.

I just hate when my professors do this and when students who know better do it. I don't like dumbing down for the sake of teaching.

Good luck.

 

[loveoforganic]

It is a trend. There are exceptions to trends. There can also be other things to look for when making a determination. That doesn't get rid of the trend.

 

[docelh]

I guess all future answers should include every possible exception and a multi-page long answer to leave no stone un-turned. Pointless.

I'm answering the OP's original question, not writing a Supreme Court brief to anticipate Justice MegaSpectacular's nitpick counter-arguments and exceptions. This is O-chem pal... there are no ironcad rules. If you interpreted my lower case law to be a universal truth, that's your problem. And if my answer doesn't satisfy your nitpick attitude, you can shove it up your...

The quibbles raised by a particular poster here and on the enolates question is just plain petty. Period.

As for your counter-argument of -COOH and -CN, that is on its face factually inaccurate as the the C atom has three bonds total in both cases.

 

[MegaSpectacular]

As for your counter-argument of -COOH and -CN, that is on its face factually inaccurate as the the C atom has three bonds total in both cases.

lol. Yeah, it has 3 bonds in both cases AND the EN is greater in -COOH than in -CN. No matter how you look at it, adding up the EN doesn't help understand the concept. Rethink criticizing this example.

 

[BerkReviewTeach]

lol. Yeah, it has 3 bonds in both cases AND the EN is greater in -COOH than in -CN. No matter how you look at it, adding up the EN doesn't help understand the concept. Rethink criticizing this example.

What ever happened to good old fashioned resonance?

In the -CN cases, the carbon has three bonds pulling electron density away by the inductive effect, and two pulling electron density away by resonance, therefore it's highly withdrawing. In the -COOH case, the carbon has three bonds pulling away by the inductive effect, one pulling away by resonance and another donating by resonance, therefore it's mildly withdrawing. The difference here is due to resonance.

LoveofOrganic gave a great example where only inductive effect was applicable, and the additive effect was right on the mark. When it's the inductive effect only, additive does work out, exactly as he (or she) said. You countered with an example showing that the additive approach doesn't work in some cases, where the fundamental reason was because of resonance. The argument is not who's correct (given that you both are), but "when do you consider resonance versus when do you consider the inductive effect?"

Let's come up with a general set of rules to explain acidity.

• Relative acidity rules
  1) EWGs increase acidity and EDGs decrease acidity
  
  2) Resonance is more important than inductive effect
  
  3) For resonace, EDG have lone pairs that can be shared into the pi-system. EWG have pi-bonds that can pull away electrons from the atom with the protic hydrogen.
  
  4) For the inductive effect, proximity (distance from the protic hydrogen) and quantity (the more electronegatiove atoms present, the greater the effect) impact its strength.

Please pile on more and build the list.

 

[MegaSpectacular]

What ever happened to good old fashioned resonance?

In the -CN cases, the carbon has three bonds pulling electron density away by the inductive effect, and two pulling electron density away by resonance, therefore it's highly withdrawing. In the -COOH case, the carbon has three bonds pulling away by the inductive effect, one pulling away by resonance and another donating by resonance, therefore it's mildly withdrawing. The difference here is due to resonance.

LoveofOrganic gave a great example where only inductive effect was applicable, and the additive effect was right on the mark. When it's the inductive effect only, additive does work out, exactly as he (or she) said. You countered with an example showing that the additive approach doesn't work in some cases, where the fundamental reason was because of resonance. The argument is not who's correct (given that you both are), but "when do you consider resonance versus when do you consider the inductive effect?"

Let's come up with a general set of rules to explain acidity.

• Relative acidity rules
  1) EWGs increase acidity and EDGs decrease acidity
  
  2) Resonance is more important than inductive effect
  
  3) For resonace, EDG have lone pairs that can be shared into the pi-system. EWG have pi-bonds that can pull away electrons from the atom with the protic hydrogen.
  
  4) For the inductive effect, proximity (distance from the protic hydrogen) and quantity (the more electronegatiove atoms present, the greater the effect) impact its strength.

Please pile on more and build the list.

wow, thoughtful response that is coherent and will actually help the OP👍. These are the ones I enjoy reading.

 

[Lacipart]

OP here, thanks BerkReviewTeach, the thread was getting pretty confusing before you posted 🙂

Makes pretty perfect sense right now, woo-hoo!