NMR question Watch

Merdan
Badges: 10
Rep:
?
#1
Report Thread starter 5 years ago
#1
On one of the NMR question I found the structure using hydrogen NMR and infrared spec
I found it was ester and I throught it would be C2H5COOCH3 but the answer was
CH3COOC2H5 and on the mark scheme it says don't accept C2H5COOCH3. How do I distinguish it from NMR spec. Do any of you guys understand the term peak being furthest downfield cuz it says there must be another peak furthest downfield for it to be
C2H5COOCH3. I really need help on this..
0
reply
EierVonSatan
Badges: 19
#2
Report 5 years ago
#2
You can tell between those two using the ppm values and the integration of the peaks.

So for CH3COO- you would expect a peak at about 2.1 ppm with integration 3.

furthest downfield = highest ppm
0
reply
BJack
Badges: 19
Rep:
?
#3
Report 5 years ago
#3
You can tell from the splitting pattern (singlet vs quartet) and peak integral (3 vs 2 protons) which way round the alkyl groups are attached. The highest-shift protons (i.e. the furthest downfield) will be the ones on the carbon bonded to oxygen. This is because oxygen is electron-withdrawing, so the closer oxygen is to the protons, the more deshielded the protons are.
0
reply
Merdan
Badges: 10
Rep:
?
#4
Report Thread starter 5 years ago
#4
(Original post by BJack)
You can tell from the splitting pattern (singlet vs quartet) and peak integral (3 vs 2 protons) which way round the alkyl groups are attached. The highest-shift protons (i.e. the furthest downfield) will be the ones on the carbon bonded to oxygen. This is because oxygen is electron-withdrawing, so the closer oxygen is to the protons, the more deshielded the protons are.
Its also got integration patterns on which are 23-29-30 for 3 different environments. How do you derive 3 vs 2 protons and what does it tell you? Sorry I didn't study integration part of the nmr spec as I haven't got it in my notes so would be great if you go into detail pls?
0
reply
BJack
Badges: 19
Rep:
?
#5
Report 5 years ago
#5
(Original post by Merdan)
Its also got integration patterns on which are 23-29-30 for 3 different environments. How do you derive 3 vs 2 protons and what does it tell you? Sorry I didn't study integration part of the nmr spec as I haven't got it in my notes so would be great if you go into detail pls?
The peak integral helps you work out how many protons there are in a particular environment: the ratio of the peak integrals is the ratio of the number of protons in different environments. It's not 100% accurate, so you will often need to round sensibly. In this case, you can reasonably divide by 10 and round to say that your integrals are 2:3:3 — these are the number of protons you have in each environment.

In this case, if the two proton integral has highest shift, you can tell that the -C2H5 chain is attached to an oxygen. If the highest shift corresponds to a three proton peak, you can conclude that -CH3 is attached to the oxygen.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • Bournemouth University
    Clearing Open Day Undergraduate
    Wed, 31 Jul '19
  • Staffordshire University
    Postgraduate open event - Stoke-on-Trent campus Postgraduate
    Wed, 7 Aug '19
  • University of Derby
    Foundation Open Event Further education
    Wed, 7 Aug '19

Are you tempted to change your firm university choice on A-level results day?

Yes, I'll try and go to a uni higher up the league tables (139)
17.62%
Yes, there is a uni that I prefer and I'll fit in better (74)
9.38%
No I am happy with my course choice (464)
58.81%
I'm using Clearing when I have my exam results (112)
14.2%

Watched Threads

View All