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This is the answer to chapter 19, problem number 65, from the smith organic chemistry textbook.
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And in this problem, we're asked to draw two amino acids at their neutral, positively charged, and negatively charged forms.
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And we're asked which form predominates at ph 1, 6, and 11.
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And then we're asked, what is the structure of each amino acid at the isoel? electric point.
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Okay.
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So first we're asked about methyonine, and we're told that the side chain of methyonine is ch2, ch2, s -c -c -h -3.
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So to start, you can draw.
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Okay, well, so we'll do a on this top line.
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So we'll start with the neutral form.
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And the neutral form, and the neutral form, is going to be the zwitter ion.
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So we have a central carbon.
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We have the carboxylic acid, which is going to be deprotonated.
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We have a hydrogen on our central carbon.
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Then we have the amine, which is going to be protonated in the zitter ion form.
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And then we have our side chain.
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The side chain here was ch2, ch2, s -c -h -3.
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So that's our zwitter ion, our neutral form of this molecule.
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And i'm actually going to move this over just a little bit.
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There we go.
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And so the positively charged version of this molecule is going to have the protonated amine but we'll also have the carboxylic acid protonated.
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So here's our carboxylic acid protonated, so there's no charge there.
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Here's our amine protonated.
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So that's where the positive charge comes from.
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And then our side chain is unaffected here.
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So that's going to look exactly the same.
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The negatively charged version of this molecule is going to be exactly the opposite.
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So we'll have the deprotonated carboxylic acid, and then we will have the not protonated amine.
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So nh2 with no positive charge on it.
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Ch2, ch2, ch3...