The spectrum shown here is for a molecule with a molecular for...

Question

The spectrum shown here is for a molecule with a molecular formula of C₄H₉Cl. Suggest a structure for this molecule.

Accepted Answer

Hello everyone. Let's do this problem. It reads what is the structure of the compound that has the following proton N M R spectrum data and molecular formula of C five H 11 C L. We have four signals. The first signal has an integration of one proton and is a quintet at 3.38 P PM. The second signal is integrated with one proton and is an octet at 1.91 P pm signal three is a three hydrogen doublet at 1.55 P PM. And the fourth signal is a six hydrogen doublet at 60.88 P PM. And we are given four answer choices. Answer choice A is neo penal chloride. Answer choice B is two Chloro pentane. Answer choice C is one Chloro two methyl butane and answer choice D is two Chloro three methyl butane. So how can we use our N M R data to determine the structure? Well, we're given the molecular formula. And if our answer choices had various characteristics of uns saturation, we could calculate the index of hydrogen deficiency to help us. But I noticed that all of my answer choices are fully saturated. So we don't have to do that, but we can look at a few di different characteristics of these N M R signals. The first one being how many signals are being produced by each structure. Then we can look at the integration of each of those signals, we can look at the multiplicity which tells us how many neighboring protons we have, right? Because we use the expression N plus one where N is the number of neighboring protons. And lastly, we can look at their chemical shift and that's determined by what is surrounding that proton, right? Any electron withdrawing groups, for example, an electron negative atom will draw that negative those negative electrons away from the proton leaving it naked and de shielded, which will make it go more downfield and have a higher chemical shift. So let's look at each of these structures and see what characteristics match the ones that are given to us in the data. So answer trace A will produce how many signals. Well, it will produce one signal for this, these three methyl groups, right? Those are all equivalent protons and it will produce one signal for these methylene protons. So that is only two signals. So we know that answer choice A cannot be correct because we have four signals given to us in the data. Alright, let's see. Answer choice B we will get 1234 signals. OK. That's a possibility. Answer choice C will give us for five signals. That means we cannot have answer choice C as a correct answer. And answer choice D will have one, 234 signals. So that means answer choices B and C and D are our only possibilities. All right. So now we looked at the number of signals, let's move on to integration. So what will be the integration of these four signals in each compound? So looking at answer choice B signal one will have three protons. Signal two will have two protons. Signal three represents two protons and signal four represents three protons. So we have 3223. Well, that doesn't match our integration of 113 H sorry 1136. So answer choice B cannot be correct. So by process of elimination, we know answer choice D is going to be our correct answer. But let's double check. So signal one has six protons. Signal two has one proton signal three has one proton and signal four has three protons. So 61136113 that matches our answer or sorry. Our data given to us, if you want to stick around, we can keep going through the multiplicity and chemical shift. So let me move this info out of the way. So signal one has those two methyl groups have one neighboring proton. So that will be a double it, which matches our data six H double it. Signal two has 67 protons. So that will be an octet, which we do have a one H octet. Signal three has 12345, no, 1234, neighboring protons four plus one is five. So that is a quintet and we have a one inch quintet and our signal four has one neighboring proton. So that is a three H double it, which we do have. All right, let's look at the chemical shift, the proton closest to this electron negative chlorine is going to have the highest chemical shift. So it makes sense that signal three, our quintet has the highest chemical shift at 3.38 P pm, right? Because it is right, that it's attached to the same carbon as the chlorine atom. All right, then the next most downfield signal is 1.91 P PM R one H octet. So that is signal two. And that's going to be more downfield than signal four because there is only one proton on that carbon. So it doesn't have to share the carbon with any other protons. So that is our 1.91 P PM. That makes sense. Our sixth hydrogen doublet we know is going to be the lowest chemical shift because it is furthest away from that chlorine atom. And there are a lot of hydrogen sharing those carbons. So that is our 0.88 P pm. And our three H doublet signal number four is the next most upfield at 1.55 P PM. And again, because it is a little bit further away from that chlorine atom. So once again, D is the correct answer for this problem. That's it for this one. I hope this was helpful. And thanks for watching.

The spectrum shown here is for a molecule with a molecular formula of C₄H₉Cl. Suggest a structure for this molecule.
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Key Concepts

Molecular Formula Interpretation

Spectroscopy Analysis

Isomerism in Organic Chemistry

The spectrum shown here is for a molecule with a molecular formula of C₄H₉Cl. Suggest a structure for this molecule.<IMAGE>

Key Concepts

Molecular Formula Interpretation

Spectroscopy Analysis

Isomerism in Organic Chemistry

The spectrum shown here is for a molecule with a molecular formula of C₄H₉Cl. Suggest a structure for this molecule.
<IMAGE>