person 34
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Totally confuses me. I, annoyingly, missed all the lessons on it and have tried to teach it to myself. I don't get it, basiaclly.

So, firstly what is an intergration thingy? If you get the ratios given to you, surely it's compleltely irrelevant?

Secondly, the heights of all the peaks are totally random. They're mean to correspond to the ratio of hydrogens, but they don't e.g, CH2 and OH have the same height of peak, so what's that about?

Also, what is the area under the peak???? It's all the same so yeah what's going on there?

Ta
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charco
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The integral is the area under the peak.

The ratio of the integrals is the same as the ratio of number of atoms causing the peaks, and as such is very useful

eg in ethanol CH3CH2OH the integrals have a ratio of 3:2:1
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ConservativeNucleophile
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(Original post by person 34)
So, firstly what is an intergration thingy? If you get the ratios given to you, surely it's compleltely irrelevant?
(Original post by person 34)
Also, what is the area under the peak???? It's all the same so yeah what's going on there?
When reading NMR spectra, there are three characteristics to be aware of:

  1. The chemical shift value
  2. The integration value
  3. The splitting pattern

The chemical shift identifies the environment in which the protons exist. Chemical shifts are caused by the surrounding atoms in the molecule withdrawing electron density from a particular proton (remember "proton" is used in the context of H nuclei in NMR) environment, leaving those protons less shielding from the magnetic field of the spectrometer. Remember that these values are given to you in the exam, so don't waste time memorising them.

The integration value quantifies how many protons are present in a particular environment. In exams, you'll always receive a clean ratio (like ethanol's 3:2:1 mentioned by charco).

The splitting patterns identify how many protons there are in adjacent environments (if there are no adjacent environments, you have a singlet peak), which is due to the spin-spin coupling between protons of the two environments.

Once you understand that, it's really a case of practice makes perfect. Exam papers have a tendency to lead you through a question by asking you to identify each environment (i.e. peak) individually, then asking you to piece together the molecule by joining each environment in a logical manner.
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person 34
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(Original post by ConservativeNucleophile)
When reading NMR spectra, there are three characteristics to be aware of:

  1. The chemical shift value
  2. The integration value
  3. The splitting pattern

The chemical shift identifies the environment in which the protons exist. Chemical shifts are caused by the surrounding atoms in the molecule withdrawing electron density from a particular proton (remember "proton" is used in the context of H nuclei in NMR) environment, leaving those protons less shielding from the magnetic field of the spectrometer. Remember that these values are given to you in the exam, so don't waste time memorising them.

The integration value quantifies how many protons are present in a particular environment. In exams, you'll always receive a clean ratio (like ethanol's 3:2:1 mentioned by charco).

The splitting patterns identify how many protons there are in adjacent environments (if there are no adjacent environments, you have a singlet peak), which is due to the spin-spin coupling between protons of the two environments.

Once you understand that, it's really a case of practice makes perfect. Exam papers have a tendency to lead you through a question by asking you to identify each environment (i.e. peak) individually, then asking you to piece together the molecule by joining each environment in a logical manner.
Hmm ok, that does simplify it a bit! I just did an exam question and got some of it right, but I still always manage to get the overall structure wrong. Still, as you say it's one of these things where practise actually makes a difference. THANKYOU conservativenucleophile. Love the name as well!
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ConservativeNucleophile
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(Original post by person 34)
THANKYOU conservativenucleophile. Love the name as well!
Cheers!

Good luck with your chemistry.
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MulderMan
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Thanks for this as well, I have nmr theory memorised off by heart, but for some reason the whole of A2 chem hasn't been taught how to interpret nmr spectra!
Where about in sunny Warrington are you?
Didn't realise there were too many chemists here!
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ConservativeNucleophile
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(Original post by MulderMan)
Where about in sunny Warrington are you?
Didn't realise there were too many chemists here!
Ahh, another Warringtonian! I'll PM you my location now...

I just checked your profile; I've got quite a few friends who go to Priestley! :cool:
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~tifa
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I want to have a go at explaining too.. simply because it'll help me remember all this jazz a bit more too haha

so here we go:

Nuclear Magnetic Resonance is used mostly in medicine to obtain images of soft tissues, called Magnetic Resonance Images. It is mostly used to identify H nuclei.
These only get detected once they flip whilst spinning.
"flipping" is when spinning nuclei change thier orientation from with the feild to against the feild.
The absorption of energy that makes the nuclear spin flip is called Nuclear Magnetic Resonance.
The NMR behaviour is a property of the nucleus, however protons (essentially H) in different enviornments (which is basically the different positions in a molecule) have different NMR spectra.
The areas under the peak suggests ratio of the protons. The protons in different enviornment gives peak at different feild strengths, so basically the ratio of the areas of the peaks is the ratio of the numbers of protons of each type.
The integration trace is propotional to the area of the peak and therefore to the number of protons responsible for that peak. so say in ethoxyethane (C2H5OC2H5), there are 10 protons. These will form a set of 4 and a set of 6.so like 4 protons in two CH2 and 6 protons in two CH3.

I see, I need to understand the spin-spin thingy myself..so I'll get back on that one

good luck for the exam tomorrow. hope its not a pain. uhh.

(Original post by ConservativeNucleophile)
The splitting patterns identify how many protons there are in adjacent environments (if there are no adjacent environments, you have a singlet peak), which is due to the spin-spin coupling between protons of the two environments.
Does a singlet peak also means that the H is not attatched to a Carbon?

Also, how do we identify Labile protons or more importantly, what are Labile protons?

am I asking stupid questions? ..ooh.
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