March 28, 2024, 06:35:55 AM
Forum Rules: Read This Before Posting


Topic: NMR peak for alcohol at 12.5 ppm  (Read 6412 times)

0 Members and 1 Guest are viewing this topic.

Offline nace17

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
NMR peak for alcohol at 12.5 ppm
« on: May 02, 2014, 02:49:01 AM »
My teacher gave a molecule: benzene with a methoxy group, an alcohol group, and a ketone group. He asked why does the hydrogen in the alcohol group have a peak 12.5 ppm on the NMR. My hints were 6, water, and DNA. I have done a ton of research and haven't been able to find much of anything relating to my molecule. The only things I have found are imino protons and Watson and Crick base paring. Those are my two best guesses as of this moment. Open to any and all suggestions thank you!!
« Last Edit: May 02, 2014, 03:03:57 AM by nace17 »

Offline nace17

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
Re: NMR peak for alcohol at 12.5 ppm
« Reply #1 on: May 02, 2014, 02:57:07 AM »
Here is a picture of the molecule if that helps at all.

Offline Archer

  • Chemist
  • Sr. Member
  • *
  • Posts: 1001
  • Mole Snacks: +85/-20
  • Gender: Male
Re: NMR peak for alcohol at 12.5 ppm
« Reply #2 on: May 02, 2014, 03:07:29 AM »
1 draw your aromatic system properly! You will lose marks for that.

2 draw your bond angles properly

3 rotate the ketone group so it is closer to the OH. How do hydroxyl groups interact with carbonyls?
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

Offline nace17

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
Re: NMR peak for alcohol at 12.5 ppm
« Reply #3 on: May 02, 2014, 03:14:20 AM »
Sorry about the aromatic I had to redraw it quickly for the picture. Does the carbonyl and the hydroxyl make an acetyl?

Offline Archer

  • Chemist
  • Sr. Member
  • *
  • Posts: 1001
  • Mole Snacks: +85/-20
  • Gender: Male
Re: NMR peak for alcohol at 12.5 ppm
« Reply #4 on: May 02, 2014, 03:18:17 AM »
No, what is one of the most fundamental properties of hydroxyl groups?

Think about your teachers comment on water
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

Offline nace17

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
Re: NMR peak for alcohol at 12.5 ppm
« Reply #5 on: May 02, 2014, 03:24:17 AM »
The polarity of the hydroxyl group. And water is also polar.

Offline Archer

  • Chemist
  • Sr. Member
  • *
  • Posts: 1001
  • Mole Snacks: +85/-20
  • Gender: Male
Re: NMR peak for alcohol at 12.5 ppm
« Reply #6 on: May 02, 2014, 03:32:07 AM »
Any thing else? Why does water have such a high boiling point relative to methane even though their masses differ by only 2 AMU?
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

Offline nace17

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
Re: NMR peak for alcohol at 12.5 ppm
« Reply #7 on: May 02, 2014, 07:48:20 AM »
Besides bond strength and hydrogen bonding I have no idea

Offline Archer

  • Chemist
  • Sr. Member
  • *
  • Posts: 1001
  • Mole Snacks: +85/-20
  • Gender: Male
Re: NMR peak for alcohol at 12.5 ppm
« Reply #8 on: May 02, 2014, 09:18:46 AM »
Besides bond strength and hydrogen bonding I have no idea

What would and O-H hydrogen bond to in your molecule if you rotated some bonds?

O=C(C)C1=CC=C(C=C1O)OC

The SMILES output above gives a better conformation.
« Last Edit: May 02, 2014, 09:44:04 AM by Archer »
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

Offline orgopete

  • Chemist
  • Sr. Member
  • *
  • Posts: 2636
  • Mole Snacks: +213/-71
    • Curved Arrow Press
Re: NMR peak for alcohol at 12.5 ppm
« Reply #9 on: May 02, 2014, 09:38:04 AM »
… only things I have found are imino protons and Watson and Crick base paring.

I am not an expert on NMR theory. I only have empirical knowledge. I presume the base paired hydrogens are shifted to low fields. Carboxylic acids are also shifted to low fields. Carboxylic acids have characteristic IR spectra presumably due to hydrogen bonding. If so, what might that tell you about your structure?
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

Offline Archer

  • Chemist
  • Sr. Member
  • *
  • Posts: 1001
  • Mole Snacks: +85/-20
  • Gender: Male
Re: NMR peak for alcohol at 12.5 ppm
« Reply #10 on: May 02, 2014, 09:46:50 AM »
I was making compounds like this which had a similar phenolic proton δ=18-19 ppm is this value upfield or downfield from TMS?

What does that tell you about the proton is it sheilded or desheilded?
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 5594
  • Mole Snacks: +319/-22
Re: NMR peak for alcohol at 12.5 ppm
« Reply #11 on: May 02, 2014, 09:58:29 AM »
Interesting.  I don't suppose you did any other studies on it, like its fractionation factor or its H-2 NMR shift?  I used to do such things in a previous life.

Offline Archer

  • Chemist
  • Sr. Member
  • *
  • Posts: 1001
  • Mole Snacks: +85/-20
  • Gender: Male
Re: NMR peak for alcohol at 12.5 ppm
« Reply #12 on: May 02, 2014, 11:04:51 AM »
Interesting.  I don't suppose you did any other studies on it, like its fractionation factor or its H-2 NMR shift?  I used to do such things in a previous life.

No, I have to be honest I don't know what those things are. I haven't lost the oportunity I have plenty of sample and a friendly technician who would run them. What are they?
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 5594
  • Mole Snacks: +319/-22
Re: NMR peak for alcohol at 12.5 ppm
« Reply #13 on: May 02, 2014, 11:29:30 AM »
When one sees downfield hydrogens one may have what are called short, strong hydrogen bonds or low-barrier hydrogen bonds.  One might see that the value of the fractionation factor that is much less than one and/or a significantly nonzero value of δH - δD when comparing the two chemical shifts.  The fractionation factor is a measure of whether a given exchangeable group would prefer to have hydrogen or deuterium at that site.  Maurice Kreevoy did some of the early work on the organic chemistry of these H-bonds.  It has been a controversial topic in enzymology.  See for example, "Strong, Low-Barrier Hydrogen Bonds May Be Available to Enzymes" dx.doi.org/10.1021/bi4014566 | Biochemistry 2014, 53, 344−349

Offline Archer

  • Chemist
  • Sr. Member
  • *
  • Posts: 1001
  • Mole Snacks: +85/-20
  • Gender: Male
Re: NMR peak for alcohol at 12.5 ppm
« Reply #14 on: May 02, 2014, 11:55:52 AM »
That's fascinating, these were only small molecules RMM = 400 ish and very unreactive at that hydroxyl group.

The hydrogen bond was so strong that you got clear HMBC data through it.

We had one which would tautomerise between two forms in chloroform give a 7:3 ratio of δ19.23 and 18.39 respectively.

How does the experiment work, you just do a simple D2O shake? or is it a bit more involved?
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

Sponsored Links