Dear Prabodh,

The mass spectrum is indicative of an aliphatic compound that is most probably a methyl ester (as you assumed yourself) or a 2-methyl carboxylic acid. If it were a methyl ester and its molecular weight 170, it could be one of the isomeric methyl nonenoates. However, although the spectrum does not rule out this possibility, your spectrum does not match any that I looked up for methyl nonenoates (there is much more fragmentation arising from the unsaturation, i.e. m/z 55, 69, etc). Moreover, the retention indices for methyl nonenoates are some 100 units lower that that you determined.

The spectrum gives little additional direct indication of the presence of any other functionality. I did not notice any hint of chlorine presence (looking for a pair of fragments differing in two mass units and having roughly 3 : 1 intensities ratio in favor of the lower mass).

There is a loss of 18 from the alleged M+, which can also occur as a non-specific fragmentation of esters, and is not a clear-cut indication of the presence of an alcohol.

My advice to you would be to analyse the rest of the chromatograms and see if there are any related compounds to this one. Perhaps it is a part of a series of homologous compounds and perhaps some of them might luckily have there MS in a data base you have at your hands. Additionally, look up the literature for the composition of Thymus and Origanum essential oils, these might provide some clues.

If I were you, I would do some chemical transformations of the samples, derivatize them (try to form silyl ethers to check for a possible alcohol, or hydrogenate and form dimethyldisulfide adducts to verify if it is an alkene).

It is quite possible that the m/z 170 is not the molecular ion.

If you have any additional data I would be glad to give you my opinion.

Good luck in your work,

Niko

If 170 is M+, you have ...170-152=18 (H2O), 170-139=31 (CH2-OH)...looks like an alcohol with a ramification CH3-CH-CH3=43, but you can do an TLC to see if is an alcohol (n-hexan:diethylether=10:1)...looks like 9-methyl-5-decen-1-ol.

Thanks everyone for your input. This is mass spectrum of trace component, so its not practical to perform derivatization as Niko said. Andre, I looked on lipid library could not find this mass spectrum. Thanks for cool link, its really useful, probably in future it will be heavily used. 

Luliana, I tried to find MS of 9-methyl-5-decen-1-ol on NIST webbook. Is this MS available in any commercial libraries? Unfortunately its multi-component samples so could not perform TLC. 

One of the most common sources of unidentifiable spectra is peak overlap. Are you sure that there is only one compound in the peak - if you look at spectra from different times across the peak do all the ions rise and fall together ? If not you have a co-elution and the spectrum is of a mixture of (at least) two compounds.

Unfortunately in this moment our GC-MS is broken and I can"t open the MS Wiley library.

Peter is right, can also be mixture of  isomers.

YOu could try some denconvolution software such as AMDIS or others which may help.

Dear Prabodh,

I agree with the most of  above suggestions  on MS interpretation. I think that our knowledge about MS fragmentation could be greater if we could  see the first peaks of ions occuring at m/z  range from 15 to 40. I expect to see peaks at m/z 31 (from alcohols) or 35 and 37 (from compounds containing Cl?).