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Hello everyone, today we're doing chapter 14 problem 76 and we're shown this molecule here and it says that we get two h &mr proton signals we have one signal that corresponds to 12 protons quite downfield shifted at 8 .9 ppm and then we have another signal corresponding 6 protons at a very shielded negative 1 .8 ppm and it says using a similar argument that that is used to offer the chemical shift values for the benzene protons.
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Explain why the shielded and deshielded values are observed in this molecule here.
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Well, we're told that we have two different types of protons.
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So let's see if we can identify them.
00:49
Well, let's start by drawing.
00:52
We have these alkyne bonds that are all conjugated to each other.
00:56
So we have a proton that goes up here, here, here.
01:06
So i'm drawing all the protons that go on outside of this molecule.
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So if we see we actually have 2, 4, 6, 8, 10, 12 protons on the outside.
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On the inside, we have 6 protons.
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So this corresponds to the 12 and 6 protons that we see in the question stem.
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But now what the reason for the outer protons being highly deshielded at 8 .9, and the inner protons being extremely shielded at minus 1 .8.
01:48
Well, we have 18 pi electron due to the nethered...