[Telamond]

Hello, I'm an organic chemist and I've tried to analyze my allylsilane compounds on the MS (ESI+), but they seem to be decomposing and I can't see the peaks at where they should be.
Is there any specific reasons for this? Should I use some kind of derivatization?

Any input is helpful, thank you.

[MOTOBALL]

1) Are your compounds of the general type CH2=CH-CH2-Si-R3  (NOT Si-O-Si siloxanes) ??

2) Is your mobile phase MeCN/water or other ??

3) Do you see hydrolysis products ??

Suggest you use non-protic solvents (e.g. MeCN) with a small amount of silver tetrafluorborate (ca. 10 mg/100 mL) to generate [M + Ag]+ ions; these are very obvious due to the Ag 108/110 doublet (~1:1 intensity)

Also possibly run in CH2Cl2 in -ve mode, see [M + Cl]- ions; again, very obvious due to Cl 35/37 doublet (~3:1 intensity).

You are ONLY allowed to act on these options if you report back the results---whether they are successful or not.  Seriously, we all learn from the negative results as well as
the positive.

Good Luck !!

[MOTOBALL]

My first response was to answer the question you asked regarding ESI.

My second response is to answer the question you did not ask.  If these samples came into my lab. I would suggest Chemical ionization (CI)-MS, either direct insertion probe for solids or GC/MS for liquids, to determine MW if you are just checking "did I make it ?"
or electron impact EI for a fingerprint spectrum for structural elucidation.

[Telamond]

Thank you for your answer and sorry for the delay in replying!
I've been writing my master's thesis the last week and have not been able to be in the lab at all.
I will try using it with MeCN and silver tetrafluorborate when I get back and I'll get back with the results!

The products are also:  R-CH=CH-CH2-SiMe3

[Telamond]

Method worked for almost all of my compounds except one. My professor suspects that that compound that it didn't work on was because it's hard to ionize and form adducts.

[MOTOBALL]

I'm glad that the [M+Ag]+ method worked; could you give the structure of the one compound  that was not amenable to this method ??

In terms of why did one compound fail to be detected, you don't actually ionize the compound itself by this technique---a complex is formed by the Ag+ ion with the neutral molecule, usually with pi electrons of a double bond.

                        M + Ag+    [M + Ag]+

Thanks for posting your results !!!!!!