Proton NMR What am I missing?

Original post by Lawbringer

I honestly feel I am missing something major and therefore can't finish this question off, which I think would be essential to all NMR questions.

Okay, I got most of the vital info but I just don't know which to choose?

Can you show the whole question?

Reply 2

Lawbringer

OP

11

Original post by alow

Can you show the whole question?

Reply 3

Original post by Lawbringer

I honestly feel I am missing something major and therefore can't finish this question off, which I think would be essential to all NMR questions.

Okay, I got most of the vital info but I just don't know which to choose?

Hi, I don't think you're missing anything. The spectrum must be for ester (CH3)2CHCOOCH3. Distinguishing peak is the one split into 7 at 2.7ppm. (It's HC-C=O adjacent to 6 Hs). This (multiplet) wouldn't be present in the HNMR spectrum of the other ester (the peak at 2.7ppm would be a singlet because H in HC-C=O environment is not adjacent to any protons). Try and draw the structures out. Hope this helps :smile:

Reply 4

Original post by Lawbringer

The shift for the 3 identical methyl protons is pretty high, what can you deduce from that?

Reply 5

Original post by Terrificmagenta

x

There are two esters which match the splitting patterns. You also need to use the shifts.

Reply 6

Original post by alow

There are two esters which match the splitting patterns. You also need to use the shifts.

Which ones?? :s-smilie:

Reply 7

Original post by Terrificmagenta

Which ones?? :s-smilie:

(CH₃)₂CHCOOCH₃ and CH₃COOCH(CH₃)₂.

Reply 8

Lawbringer

OP

11

Original post by alow

The shift for the 3 identical methyl protons is pretty high, what can you deduce from that?

I have no idea what you mean? This topic is killing me. I just can't finish the questions or form the actual finished products. have you got any good resources? The OCR book is so bad at explaining this, all their questions in examples are the easiest ones ever lol /rant

I really can't make sense of how high a chemical shift can mean something?

Reply 9

Original post by alow

(CH₃)₂CHCOOCH₃ and CH₃COOCH(CH₃)₂.

No, the splitting for CH3COOCH(CH3)2 will be different. There would be no multiplet at 2.7ppm. It would be a singlet

Reply 10

Original post by Lawbringer

I have no idea what you mean? This topic is killing me. I just can't finish the questions or form the actual finished products. have you got any good resources? The OCR book is so bad at explaining this, all their questions in examples are the easiest ones ever lol /rant

I really can't make sense of how high a chemical shift can mean something?

Unless you want to know a bit more about NMR, I can't think of anything. If you do, there's some Oxford Chemistry Primers that are pretty good.

High chemical shift means that the proton's (or whatever NMR you're doing) is highly deshielded (i.e. there's less electron density around the proton). What could be a cause of this?

Reply 11

Original post by Terrificmagenta

No, the splitting for CH3COOCH(CH3)2 will be different. There would be no multiplet at 2.7ppm. It would be a singlet

It would be a septet. There is ³J coupling between the single proton and the six protons of the two methyl groups it is next to.

(edited 8 years ago)

Reply 12

Original post by Lawbringer

I have no idea what you mean? This topic is killing me. I just can't finish the questions or form the actual finished products. have you got any good resources? The OCR book is so bad at explaining this, all their questions in examples are the easiest ones ever lol /rant

I really can't make sense of how high a chemical shift can mean something?

I don't think you need to know anything about the significance of a high shift for the OCR spec :redface:

. Dw about it, you can still pick up majority of the marks even if you don't get the final structure! :smile:

I feel like a parrot rn coz i always hear my teacher say that to my friends haha. As long as you can use the n+1 rule and figure out the environments :wink:

Reply 13

Original post by Terrificmagenta

I don't think you need to know anything about the significance of a high shift for the OCR spec :redface:

. Dw about it, you can still pick up majority of the marks even if you don't get the final structure! :smile:

I feel like a parrot rn coz i always hear my teacher say that to my friends haha. As long as you can use the n+1 rule and figure out the environments :wink:

Well that's just terrible advice.

Reply 14

Original post by alow

It would be a septet. There is ³J coupling between the single proton and the six protons of the two methyl groups it is next to.

There arent any adjacent protons in the environment thoughh lol

(edited 8 years ago)

Reply 15

Serine Soul

18

Draw the displayed formulas for all the esters. Look at splitting patterns

Reply 16

Original post by Terrificmagenta

There arent any adjacent protons in the environment thoughh lol

Yes there are... Look again.

Reply 17

Lawbringer

OP

11

Original post by Serine Soul

Draw the displayed formulas for all the esters. Look at splitting patterns

Yeah if you see the 1st pic, I actually did that. It's just the final marks I really can't get, and I don't wish to settle with 7/8 lol. I really want to ace it haha

Reply 18