MCAT OChem: Resonance and Inductive Effect

[kishanb87]

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It's been a while since I have taken Ochem. I'm having some trouble with Resonance and Inductive Effect. Both TBR and TPR books don't seem to go all that in detail regarding the subjects.

When looking at the chemical properties of an atom on a molecule, which is more important to the overall electron distribution of the molecule: resonance or inductive effect?

Also, can anyone point me to some online practice for these concepts? I feel like I haven't gotten enough exposure to these concepts just yet....

Thanks!

 

[chiddler]

Resonance usually has a more prominent effect.

Best way to practice is to look up molecules and predict their relative pKa's. Example, acetic acid vs trifluoroacetic acid. Ethane vs chloroethane. Would you expect chloroform to be acidic (relative to methane)? What explains carboxylic acid acidity compared to an alcohol? Why does malonic ester anhydride have an acidic hydrogen?

So uh. Answer these questions and seek new questions yourself. Good luck.

 

[MedPR]

It's been a while since I have taken Ochem. I'm having some trouble with Resonance and Inductive Effect. Both TBR and TPR books don't seem to go all that in detail regarding the subjects.

When looking at the chemical properties of an atom on a molecule, which is more important to the overall electron distribution of the molecule: resonance or inductive effect?

Also, can anyone point me to some online practice for these concepts? I feel like I haven't gotten enough exposure to these concepts just yet....

Thanks!

Resonance usually wins. Try EK 1001. Basically every acid/base and reactivity question has something to do with resonance/induction. Always think about those when comparing things in chem/organic.

 

[SaintJude]

Answer these questions and seek new questions yourself. Good luck.

haha-you sound like yoda. great post.

 

[kishanb87]

Resonance usually wins. Try EK 1001. Basically every acid/base and reactivity question has something to do with resonance/induction. Always think about those when comparing things in chem/organic.

Yeah, I have this book. I haven't started the problems yet though. I guess I just need some experience answering these types of questions, and I should start to see a trend.

 

[milski]

Resonance usually wins. Try EK 1001. Basically every acid/base and reactivity question has something to do with resonance/induction. Always think about those when comparing things in chem/organic.

Do you know remember any examples where it does not? I'm usually the one who hates to talk in absolutes but now I'm curious if there's an example where inductive effect will be more important. I'll try to look it up eventually, but if already have an example, that would be great.

 

[MedPR]

Do you know remember any examples where it does not? I'm usually the one who hates to talk in absolutes but now I'm curious if there's an example where inductive effect will be more important. I'll try to look it up eventually, but if already have an example, that would be great.

None off the top of my head, but I didn't want to say "resonance always wins." 🙂

Obviously when there isn't resonance, then induction is the primary effect, but I can't think of a situation where both are in play and induction is stronger.

Perhaps if you have a carbonyl carbon with 2 very large, very inductive groups? Not sure.