(b) Draw the proton NMR spectrum you would expect for butan-2-one...

Question

(b) Draw the proton NMR spectrum you would expect for butan-2-one. How well do the proton chemical shifts predict the carbon chemical shifts using the '15 to 20 times as large' rule of thumb?

Accepted Answer

Hey everyone. Let's do this problem. It says right, the proton NMR spectrum you would expect for pro pan to own. How reliable is the 15 to 20 times as large rule of thumb and predicting the carbon chemical shifts. So let's break down some of the information given in the problem Pro pan to own That's also called acetone. And what does that structure look like? Well, prop is three carbons 123. And own suggests that we have a carbondale group on carbon number two, it says. So that is the following. That's this structure. Which again, that's called acetone. Let me write these metals out so we can look at the protons. And how many signals would acetone give us? How many unique non equivalent protons do we have? Well, this structure is symmetrical. Right. So these methyl protons are all going to be depicted by the same peak one. Peak. All protons are equivalent here. And are there any neighboring protons to these protons on this? Carbon? No. Right. There's the carbon with the carbonell group. So, the signal will be a single eight. Alright, and what will be the chemical shift of this signal? Well, those protons are just regular ch bonds, al caine bonds. Rate that carbon is bonded to a carbon that has a double bond to an oxygen. So there'll be a little bit more d shielded than a normal signal would be which is in 1 to 2 PPm range. So these signals will be or this signal rather will be around 2.1 PPm. For a metal proton next to a carbonell group. Alright, so, if we draw our spectrum over here, we're only going We only need to draw up to about three. Right? So that gives us something like this halfway will be About 1.5. So that oops. So we'll have one. Oh, that would have to be one and 1.5. So 1.51, two, 2.53. And our signals around 2.1 ppm. So just past two, I'll draw this line from my single it and then I will finish the line with my pen. So there's my makeshift single it there around 2.1 PPm. And the problem asked, how reliable is the 15 to 20 times as large rule of thumb in predicting the carbon chemical shifts. So this rule states that the carbon NMR shift will be about 15 to 20 times larger in value than the proton NMR shifts. So, in our case, If our proton and um our shift is two ppm 15 to 20 times as large, would be about 31.5 to 42 ppm. And for the this methyl carbon that actually works. So using the 15 to 20 rule, the chemical shift for the methyl carbon is about 31.5 to 42 PPm. The actual chemical shift for the methyl carbon is around 30.8 ppm. So the rule works fairly well. So that is the correct answer for this problem. This is our spectrum that we drew, and that makes a the correct answer for this problem. That's it for this one. I hope this was helpful, and thanks for watching.

(b) Draw the proton NMR spectrum you would expect for butan-2-one. How well do the proton chemical shifts predict the carbon chemical shifts using the '15 to 20 times as large' rule of thumb?

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