Predict which member of each pair is more acidic, and explain ...

Question

Predict which member of each pair is more acidic, and explain the reasons for your predictions.

a. cyclopentanol or 3-chlorophenol

Accepted Answer

Hey everyone and welcome back, determine which alcohol in the given pair is more acidic. Explain your choice one bit in all and to core one bit and all. We can begin solving our problem by drawing these two structures starting with one beat and all. We understand that we have four carbon atoms in our parents because we have beaten all that be one too 34. Right? So we have four carbon atoms. And at position number one, let's suppose that this is position number one. We are going to add an alcohol group. So that's one beaten all. Now two chloral one, beating all with essentially correspond to the same structure. But now at position number two over here we have our chloral substitution. So let's draw that structure 1234. And now we are going to add our alcohol group at position number one and our carbon number two contains a chloral substitution. We want to understand which of the two alcohols is more acidic. And to do that, we first will have to identify our civic hydrogen. We call that the acidic hydrogen is directly bonded to an electro negative atom. So we're going to look at this oxygen hydrogen bond right, because this hygiene is the most acidic in the structure is bonded to the most electro negative atom in our structure, all of the other hydrants are bonded to carbon atoms. And now for the other one, we're going to expand our oxygen hydrogen bond and we will just think about acidity in general. Now acidity essentially implies how easy it is for us to break that oxygen hydrogen bond these are, it is the more acidic the hydrogen is. So this is one of the ways to think about it. But we will choose a better perspective for our analysis. What if we recall a R. I. O. And draw the contract basis of the two structures. Now for this one, if we want to draw the conjugate base, we essentially have to remove that acidic hydrogen right in the form of the proton and now we are getting our conjugate base. So that would correspond to oxygen with a negative charge. Now, for the other one, if we remove hydrogen from our structure in in the form of a proton, we get the full and conjugate base. Once again, we read through our structure at let's create a better looking structure. Right. We essentially want to make sure that we have good bond angles here, so that oxygen with a negative charge, right? We are moving a proton and we are adding our chloral substitution. A R I. O. Tells us that there are several aspects which are responsible for the acidity of a specific structure. Personal atom in each case, the negative charges on oxygen. So that's exactly the same atom resonance essentially residence implies that there must be pi bonds, but we don't see any pi bonds here to think about residences. That's not the case. But I inductive effect is the key point here because if you look at the two structures, they are nearly the same except from the fact that the second structure has this chloral substitution and chloral substitution is electro negative because because chlorine is electro negative, it essentially implies that if you look at the structure where the chloral substitution responded to the negative charge were basically the lone pairs and oxygen might not be so effective in basis city of this structure. In other words, when we look at our carbon carbon bonds, right? Because chlorine is electro negative is essentially withdraws the electron density from our structure. So first of all, it's withdrawing the electrons from this carbon. But of course because we have a chain, this also implies that the electrons nearby will also be withdrawn. So the electron density on this oxygen decreases. Right, We have a lower electron density. For the first structure, we have a higher electron density. The reason for that is it's very simple because we don't have that electron withdrawing group. Right? So there's nothing that is withdrawing electrons. And this oxygen has a higher electron density. This auction has a low electron density due to the fact that chlorine is withdrawing electrons recall that base strength essential corresponds to how effective our negative charge is. In other words, are our electrons concentrated on that oxygen or are they withdrawn. So essentially we can think of these two bases as follows if this one has a higher electron density, it means it's a stronger base and this one would be a weaker base because it has a lower electron density and auction electrons are withdrawn and not so effective in participating in addition of an acidic hydrogen. So if the first one is a stronger base because it has a higher electron density and oxygen I think is withdrawing these electrons then keeping in mind that a stronger base corresponds to a weaker conjugate asset, that means this asset must be weaker. Right? Because you may always understand that whenever an acid this week that would produce a strong conjugate base and vice versa. If the base is strong then we are producing a weak conjugate asset and similar here if we have a weaker base that would correspond to a stronger asset. So that's how we are thinking about this problem between the two structures. Because the second one has a lower electron density, it's a weaker base and because it's a weaker base it would correspond to a stronger conjugate asset. So you can say that the second structure two chlor a one beautiful, would be a stronger asset between the two. And the reason for that is the inductive effect. This structure contains glory in that is electron withdrawing and therefore weakening that oxygen hydrogen bond and as a result producing a weaker base right now, based on our analysis, We can conclude that the correct answer to the multiple choice question is C2 chloral one beat analyst more acidic than one, beating all due to the invective effect of the chlorine atom. Thank you for watching.

Predict which member of each pair is more acidic, and explain the reasons for your predictions.
a. cyclopentanol or 3-chlorophenol

Key Concepts

Acidity and pKa

Inductive Effect

Resonance Stabilization

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