[mikeja]

Hello,

I need help with analyzing a hydrocarbon.  I estimate a halogenated hydrocarbon, 5-8 carbons in length. I could be wrong, and I don't deal with this type of compound often.

A little background info: I analyzed a solution and was told it was a hydrocarbon with isopropanol. So I figured I could just run it easily on my gcms.  Turns out it clogged the detector and column like crazy, and I ran isopropanol through the column for a few hours to clean it out.  All I can tell is there are some low MW aromatics coming out early, and then the product that comes out at around 8 minutes is highly concentrated and sticks to my column.  I'm guessing this is a halogenated hydrocarbon from the M+2 peaks, but don't often look at this type of molecule.  These peaks don't look like bromine M+2, so possibly a saturated chlorine alkane? or oxygenated hydrocarbon, although it doesn't look like a polyethylene glycol.

Then I decided to run some NMR's. The GCMS and HNMR are posted here, the next post will have the C13.  It looks like a simple enough spectra, so any help is appreciated.

Edit - the NMR solvent is chorloform-D, and there is some small amount of isopropanol in the mixture, so the peaks may not look pristine.  Also, the small MW aromatics that are seen on the GCMS are not seen on the HNMR because they are only a low percentage of the mix. The first GCMS shows the detector being clogged, the ion spectra below it are designating the early eluting aromatics, you can see from the 77 peak.  The second GCMS is showing the major component, it's a hydrocarbon b/c of all the +12MW peaks, but the +2 ion peaks are escaping me.

Thanks,
Mike

[mikeja]

First one is HNMR, zoomed in.  Second two are CNMR's in CDCl3, and there should be an isopropanol peak in there.

[ATMyller]

If you neglect the isopropanol and CDCl₃ peaks from HNMR (everything after the 1.39 ppm one) and from CNMR (everything after the 37 ppm one) the only possible halogenated or oxygenated hydrocarbons are ketones and terminal halogens -CH₂-X (X = Cl, Br of I).

Also the HNMR peaks at 1.24 and 0.85 are typical for long chained -(CH₂)_n-CH₃ or branched -(CH₂-CH₃)_n structures.

[mikeja]

Thank you,

So yes, it's most likely longer chain hydrocarbons.  That also explains what I'm seeing on the GCMS, were not [M+2] isotope peaks, but rather methylene ion peaks, giving  +2 MW in high abundances. And the polarity issue makes sense as well, the hydrocarbon must be long enough to become stuck on my gcms, I'll run it on LCMS to get a better idea.

This helps a lot, thank you again. I'm not used to analyzing long chain hydrocarbons.