In my organic chemistry answer book it says that CH3CH2CO2CH2CH3 has 4 different Hydrogens and therefore 4 NMR signals and CH3CH2OCH2CH3 has 2 NMR signals. I thought that both molecules would have had 2! Can someone explain this to me?
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The first compound is an ester and looks like this:
...H.H..O...H..H
....|..|...||.....|...|
H-C-C-C-O-C-C-H
....|..|..........|...|
...H.H........H..H
If you look at it now, you can see that the molecule is not symmetrical. To see if the H's in this compound are equivalent, you can check to see how many bond lengths each H is away from the -O- group. There will be 4 signals for the H-NMR of this compound.
The second compound is an ether and looks like this:
...H.H....H..H
....|..|......|...|
H-C-C-O-C-C-H
....|..|......|...|
...H.H....H..H
This molecule is symmetrical. The two -CH3 H's will produce one signal, and the two -CH2- H's will produce one signal. That means that there will be 2 signals for the H-NMR of this molecule.
...H.H..O...H..H
....|..|...||.....|...|
H-C-C-C-O-C-C-H
....|..|..........|...|
...H.H........H..H
If you look at it now, you can see that the molecule is not symmetrical. To see if the H's in this compound are equivalent, you can check to see how many bond lengths each H is away from the -O- group. There will be 4 signals for the H-NMR of this compound.
The second compound is an ether and looks like this:
...H.H....H..H
....|..|......|...|
H-C-C-O-C-C-H
....|..|......|...|
...H.H....H..H
This molecule is symmetrical. The two -CH3 H's will produce one signal, and the two -CH2- H's will produce one signal. That means that there will be 2 signals for the H-NMR of this molecule.
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The first compound is actually ethyl propanoate, not ethyl ethanoate - and the correct name alone should tell you that the two carbon chains are different.
The carbonyl carbon is electron-withdrawing (due to the pi bond with the oxygen), thus will deshield the protons on adjacent carbons. The end result is that the proton signals will be shifted downfield (to the left, with a higher ppm chemical shift).
This deshielding, however, is different to that experienced by the protons from the ethyl chain. Since the protons are actually closer to the oxygen (3 bonds versus 4 bonds for the carbonyl group), there is a even greater level of deshielding for the protons immediately adjacent to the oxygen.
The carbonyl carbon is electron-withdrawing (due to the pi bond with the oxygen), thus will deshield the protons on adjacent carbons. The end result is that the proton signals will be shifted downfield (to the left, with a higher ppm chemical shift).
This deshielding, however, is different to that experienced by the protons from the ethyl chain. Since the protons are actually closer to the oxygen (3 bonds versus 4 bonds for the carbonyl group), there is a even greater level of deshielding for the protons immediately adjacent to the oxygen.
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Ethyl Ethanoate have 4 different environment for Hydrogen.
Edit: I am not very good with naming esters but Aaron is correct it's Ethyl Propanoate.
It's really hard to explain, for me. But here goes:
Unlike 2nd one, which is diethyl either. Ethyl Ethanoate is not symmetric on Carbonyl group. it has another oxygen attach to it. That's why each side of the functional group (center ester) is experiencing different environment. Should it have been just carbonyl group then it will be same thing as 2nd one (having only 2NMR signals instead of 4).
Edit: I am not very good with naming esters but Aaron is correct it's Ethyl Propanoate.
It's really hard to explain, for me. But here goes:
Unlike 2nd one, which is diethyl either. Ethyl Ethanoate is not symmetric on Carbonyl group. it has another oxygen attach to it. That's why each side of the functional group (center ester) is experiencing different environment. Should it have been just carbonyl group then it will be same thing as 2nd one (having only 2NMR signals instead of 4).