[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.

How do I go about this?

I'm stumped because I'm given so little data.

[tmartin]

Well, I think the idea is to use all the data together to solve the structure (obviously I know, right  )

What does the singlet at 3.7ppm indicated?  It would probably link up with the peak at 67 in the carbon, too.  You're looking for a compound with a molecular weight of 88, without groups like alcohols, carbonyls... but with a proton shifted downfield next to no other protons (what is the integration?).  You lose a fragment in the MS that adds up to 30 mass units...twice.  Perhaps this is hinting at some symmetry in the molecule.

[blueray4]

peak at 67 makes it probably an ether

i'm given no integration

[democanarchis]

Ok, so how would you make the ether symmetrical and still only have one type of proton in the 1H nmr?

[DrCMS]

Do not get fixated with it being an ether.  As tmartin suggested look at symmetrical molecules that can loose 30 twice.  Think what the 30 might be and what the 58 and 28 would be.

[Smrt guy]

Your chemical formula is either C6H16, C5H12O, C4H8O2, or C3H4O3 by mass (N and other heteroatoms have been ruled out).  Count the degrees of unsaturation in these empirical formulas.   Can you rule any out?  Then remember that you have all symmetric H and C peaks in the NMR.  Also, use the NMR chemical shifts and what they tell you.  Don't rely heavily on mass, it will only confuse you.  You can check a guess against the mass after the fact.  Also, when you have a guess you can check it on SDBS.

[blueray4]

how can you rule out a halogen in the formula?

[blueray4]

the closest molecule i can come up with is 1,4 dioxane, but it does not comply with the NMR data of there being a singlet.

[blueray4]

does coupling occur between equivalent protons?

then 1,4 dioxane would be correct

[blueray4]

ok , i pretty much decided it was 1,4 dioxane

it says the molecule undergoes alpha cleavage to produce the peak at m/z 58

then it undergoes inductive cleavage and then alpha to produced the peak at 28.

i have to come up with the mechanism for it.



m/z 58:

would the first alpha cleavage break a C-C bond, followed by a second alpha cleavage to remove OCH2?

m/z 28:

i'm confused on inductive cleavage, any explanation would be appreciated.