For each of the following substituents, indicate whether it wi...

Question

For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.

a. Br

b. CH₂CH₃

c. Chemical structure of a carbonyl group with a methyl group, illustrating concepts of acidity and electron effects.

Accepted Answer

All right. Hi everyone. So for this question, let's identify the substituent in each of the following compounds as inductively electron withdrawing electron donating by hyper conjugation, electron withdrawing by resonance or electron donating by resonance. So for part A, we have a chloral group for part B, we have a methyl group and part C we have an aldehyde. But before we talk about each of these substituent specifically, let's go ahead and discuss some of the terminology in this question, right. So first of all, recall that there are two different inductive effects, right? When you have a substituent as part of a greater molecule, it can either be what we refer to as electron donating or electron withdraw. Right. So what does that mean? Well, electron donating substituent, what they do is they donate electron density or rather they bring electrons towards the rest of your molecule? Right. So for example, in electrolytic aromatic substitution, electron donating substituent will bring electron density towards the aromatic system making it more reactive. So you might also see that electron donating groups are also referred to as activating groups for that very reason. Now, on the other hand, right, electron withdrawing groups or substitutes, they remove electron density from the rest of your molecule. So if we go back to our example, with electrolytic aromatic substitution, if our substituent is withdrawing electron density from the aromatic system, it is considered a deactivating group, right, it's making the aromatic system less reactive overall. So now with that out of the way, right, let's go ahead and discuss a couple other things that are being mentioned in the problem text, right, the first of which is hyper conjugation, right. So recall really quickly that hyper conjugation stabilizes molecules, right? And specifically, it's the stabilization, a rather stabilizing interaction, I should say between a P orbital that's not completely full and adjacent sigma bots. So when you have either an empty or a partially filled P orbital with nearby signal bonds, then there's a de localization of those electrons across your sigma bonds, right? Which increases the stability of your system. Now, resonance on the other hand, is a de localization of electrons with adjacent pi bonds, right? So when you have your pi electrons moving across your molecule, you create that de localization with different resonance structures for the same molecule. So now with that being said, let's go ahead and discuss all of our functional groups individually. Now, for part a we have a chlorine, right, which is a halogen and halogens are pretty interesting, right? Because recall halogens are incredibly electron negative, right? And if they're electron negative, then they're prone to withdraw electron density from the rest of the molecule and towards itself. So because of that halogens are considered electron withdrawing inductively, right. And specifically they are electron withdrawing. But there's another thing to, to take into account, right, because halogens have lone pairs of electrons associated to them, right? And when the when it has lone pairs of electrons, it can actually donate a pair of them towards the rest of the molecule to create different resonance structures. So not only are halogens like chlorine electron withdrawing inductively, they are also electron donating by resonance, right. So the reason I said halogens were interesting was because both of these things are true for halogens. So now moving on to our methyl group here for part B methyl groups are alco groups, right? They're hydrocarbon substituent and hydrocarbon substituent specifically have a lot of sigma bonds, right? We have either carbon hydrogen or carbon, carbon single bonds, which can participate in hyper conjugation, right. So a substituent in general are electron donating by hyper conjugation because a substituent, a substituent provides Sigal bonds to participate in that de localization, right. So it's electron donating by hyper conjugation. Last but not least we have C which is our aldehyde and aldehyde are incredibly polar, right? Because of that carbona group attached. Now because carbona groups contain that incredibly polar car bottle. It backtrack. Let me backtrack. All the hides are incredibly polar because of that car bono group, which means that inductively speaking, it's electron withdrawing, right? Because if you have something that's incredibly polar, it's going to attract electrons towards itself. But in addition to that right carbo groups contain a pi bond, right? And that pie bond can participate in a resonance. So our aldehyde and specifically our carbonyl in our aldehyde is electron withdrawing by both residents because of that pie bond and the inductive effect, right? Because it can withdraw electron density towards itself. So now with all this being said, your answer is going to be option a in the multiple choice. Mhm. So if you stuck around to the end, thank you so much for watching and I hope you found this helpful.

For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.
a. Br
b. CH₂CH₃
c.

Key Concepts

Inductive Effect

Resonance Effect

Hyperconjugation

Watch next