Original post by chem222
Someone please help me with this question!! also why is the peak at 7.4 a benzene? is it because it's a multiplet?
Someone please help me with this question!! also why is the peak at 7.4 a benzene? is it because it's a multiplet?
NMR provides structural information .
1. The position (shift) of the signal may indicate specific environments.
2. The splitting of a signal gives clues as to the neighbouring environments
3. The integral tells you how many protons are involved in the signal.
Why do you think that the signal at 7.4 suggests a benzene ring?
What other information does the NMR spectrum give you?
What information does the MS give you?
(edited 5 years ago)
The m/z is 164 so the Mr of the ester is 164. This means that the Mr of whatever structure you come up with should have this Mr.
How I'd do it is by drawing a table with 4 columns: 'Chemical Shift (ppm)', 'Integration', 'Splitting Pattern' and 'Interpretation'. For each peak, write its chemical shift, integration and splitting pattern under each respective column, and then in the 'Interpretation' column, write what you think the peak represents. This is where you use your data sheet too.
Let me give you an example, by starting with the first peak: it has a chemical shift of 2.2 ppm, an integration of 3, and its splitting pattern is a singlet. I would write these things under each respective column. Under my 'Interpretation' column, I would write something like 'This is CH3CO-. The singlet means there are no adjacent protons'. Do this for each peak and you should start to see the structure come together.
By the way, benzene is a multiplet, but that's not the reason why it has a chemical shift of 7.4 ppm. That's down to the compound itself and its magnetic properties. Benzene in this case has 5 aromatic protons, and that's what you should write for its interpretation.
How I'd do it is by drawing a table with 4 columns: 'Chemical Shift (ppm)', 'Integration', 'Splitting Pattern' and 'Interpretation'. For each peak, write its chemical shift, integration and splitting pattern under each respective column, and then in the 'Interpretation' column, write what you think the peak represents. This is where you use your data sheet too.
Let me give you an example, by starting with the first peak: it has a chemical shift of 2.2 ppm, an integration of 3, and its splitting pattern is a singlet. I would write these things under each respective column. Under my 'Interpretation' column, I would write something like 'This is CH3CO-. The singlet means there are no adjacent protons'. Do this for each peak and you should start to see the structure come together.
By the way, benzene is a multiplet, but that's not the reason why it has a chemical shift of 7.4 ppm. That's down to the compound itself and its magnetic properties. Benzene in this case has 5 aromatic protons, and that's what you should write for its interpretation.
(edited 5 years ago)
Original post by charco
NMR provides structural information .
1. The position (shift) of the signal may indicate specific environments.
2. The splitting of a signal gives clues as to the neighbouring environments
3. The integral tells you how many protons are involved in the signal.
Why do you think that the signal at 7.4 suggests a benzene ring?
What other information does the NMR spectrum give you?
What information does the MS give you?
1. The position (shift) of the signal may indicate specific environments.
2. The splitting of a signal gives clues as to the neighbouring environments
3. The integral tells you how many protons are involved in the signal.
Why do you think that the signal at 7.4 suggests a benzene ring?
What other information does the NMR spectrum give you?
What information does the MS give you?
I have watched some youtube videos and apparently it's a benzene because it's a multiplet and it says 5 protons? is this correct?
m/z is 164 so the ester produced must have an Mr of 164
2.1 is a singlet so next door to C with no H attached
2.9 is a triplet so next door to C with a 2 H
4.4 is a triplet so next door to C with 2 H
7.2 is a multiplet ....... because 5 protons there a benzene ring.... and one proton replaced by a chemical group (rest of the compound..)
2.1 is HC-CO
2.9 is HC-CO ......
4.4 IS HC-O
7.2 is C6H5
why are 2.1 and 2.9 the same?? not sure what to do after this
Original post by chem222
I have watched some youtube videos and apparently it's a benzene because it's a multiplet and it says 5 protons? is this correct?
... and because typically benzene protons appear in this region.
m/z is 164 so the ester produced must have an Mr of 164
2.1 is a singlet so next door to C with no H attached
2.9 is a triplet so next door to C with a 2 H
4.4 is a triplet so next door to C with 2 H
7.2 is a multiplet ....... because 5 protons there a benzene ring.... and one proton replaced by a chemical group (rest of the compound..)
2.1 is HC-CO
2.9 is HC-CO ......
4.4 IS HC-O
7.2 is C6H5
why are 2.1 and 2.9 the same?? not sure what to do after this
You are very close. You know that it's an ester, so there is a COO group there.
All you have to do is place one CH3 and two CH2 groups.
The splitting does not contain a multiplet (apart from benzene) so you cannot have CH2CH2CH3 anywhere
The shift of the CH3 is only 2.1 so that it is not directly attached to oxygen, hence OOCCH3
The intervening CH2 groups must be between the ester group and the benzene ring
PhCH2CH2OOCCH3
Original post by chem222
Thanks a lot for your help!! much appreciated
just one thing ......
how would we know that 2.2 and 2.8 have different groups ..... bit confusing ... as there is only one benzene group.. not two ...
just one thing ......
how would we know that 2.2 and 2.8 have different groups ..... bit confusing ... as there is only one benzene group.. not two ...
You will have been given a table of chemical shifts, or typical ranges at which specific protons appear.
The mark scheme just says that a signal at 2.2 is typical for -CH-COO- and 2.8 is typical for Ph-CH- protons.
If the proton is both then you most likely get a cumulative effect and it appears at 3. something. The chemical shifts are guides, helpful to determine which signal is most likely in the event of ambiguity.
For example CH-COO- or CH-OOC-
The first signal is expected at 2.2 while the second is expected at 4.0 ish.
The more electronegative the atom attached to the carbon holding the proton, the higher the shift value.
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