Mass Spec Problem

[blueray4]

This is what I'm given

 

No significant IR functional group signals

 

Mass spec: M+ m/z 88

Fragments at m/z 58, 50% intensity and m/z 28 100% intensity

 

H NMR: singlet at 3.7 ppm

 

13C NMR: signal at 67 ppm

 

 

I have to find the molecular formula and structure of the compound.

[Greippi]

How far have you got?

 

Once you know what chemical shift corresponds to what functional group, then it should be relatively easy to build up your compound.

 

Obviously if this is homework task then I'm not going to give you the answers, it should be pretty easy to get the information you need about what signal corresponds to what.

Edited April 26, 2010 by Greippi

[spin-1/2-nuclei]

Hi lets see if we can walk through how to solve this.

 

The first thing you want to do is look at all of your data and compare one diagnostic technique to the other, so lets see what that tells us.

 

1. You have no signal in the IR, which could be because you have no IR active functional groups (not likely) - or - the ones that are present have high level of symmetry.

 

2. you have only one signal in the proton and only one signal in the carbon - also suggesting a high level of symmetry.

 

3. you have a singlet at 3.7ppm in the proton and signal at 67ppm in the carbon - this suggests an oxygenated carbon with symmetrical hydrogens on it.

 

4. your mass spec data and the high level of symmetry suggests that you probably have more than 1 oxygenated carbon. This is because of the mw of 88.

 

5. Now lets look at your peaks in the mass spec.

The loss of 30 from 88 and 58 suggests that you have a CH2O fragment.

The loss of 28 suggests a CO fragment.

 

6. Now you have to ask yourself how many CH2 and O fragments can you get into 88.

 

7. Therefore the data suggests a dioxane. However, since this is a homework assignment I will not tell you which dioxane. You can figure this out from your data though. Remember that you have no splitting in the proton NMR, what does this tell you about the hydrogens and why?

 

you can ask more questions if you still need help. hopefully this was useful.