[meowmeow]

http://oi48.tinypic.com/2s93qyr.jpg
I'm trying to identify this unknown compound.

I uploaded a mass spec/ir spec problem that is confusing me.
The molecular ion peak looks like it is a 121 so the atomic weight is 121.
Since it's an odd number, there is a likely chance of nitrogen.
The IR Spectrum at 3000 is right in the middle of saturated/unsaturated so I guess aliphatic?

At about 1500 and 1475 there are 2 peaks which means that there is a CH3 and a CH2 group I think. Between 2000 and 1600 there's what I think is aromatic overtones but it isn't really the repetitive pattern I'm used.

With the information I have, I'm not sure how to combine them to get the compound.
I'm trying to figure out the number of carbons as a start but without elemental analysis, I'm not sure how to figure that out.

Can anyone help me identify this compound?
thanks!

[meowmeow]

Yup a night of thinking and I still can't figure it out

[MOTOBALL]

The molecular ion peak looks like it is a 121 so the atomic weight is 121.
Since it's an odd number, there is a likely chance of nitrogen

If the Molecular weight (NOT atomic wt) = 121, then the molecule MUST have an ODD (1, 3, 5, 7,....etc) number of N atoms.

The molecular ion is at m/z 106 (even MW MUST have EVEN number of N atoms (0, 2, 4,... etc); m/z 121 is just a noise signal.

The m/z 107 ion is due to isotopic contributions, e.g. ¹³C, ²H, ¹⁷O, ¹⁵N etc; measure the RELATIVE intensity of 106 to 107, and divide that number by 1.1 to give the approximate C atom count in the intact molecule.

Construct a table of m/z values vs. mass differences between successive ions---suggest possible combinations of C, H, O and N to account for these mass differences.

CLUE---the m/z 91 and m/z 77 ions are very recognisable, and are a giveaway to the core structure.

Propose as many different structures as you can, then use the IR spectrum to confirm/deny/eliminate possibilities.

Good Luck.

[meowmeow]

OMG!!! I think I might have figured it out!!!
I got Ethylbenzene. Is that right?

Thanks!
I'm gonna practice a few harder problems now which I'll probably be confused again in some other way. The final is coming up and I need an A.

[MOTOBALL]

If ethylbenzene is correct, how did you eliminate the dimethylbenzenes ??

[meowmeow]

hmm so is it
1,2-dimethyl Benzene?
since the oop stretch indicates disubstitution

[MOTOBALL]

I would have thought Ethylbenzene, due to m/z 77 (C6H5+).

However, http://webbook.nist.gov/chemistry/

gives virtually identical mass spectrum for Et-Benzene & 1,2-di-Me-Benzene (both with low-level m/z 77); you should indeed interpret your IR spectrum to differentiate EthB from the three DiMe-B isomers.  I don't have IR expertise !!!!

[orgopete]

SDBS is a good website that has the spectra of many common compounds, http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/cre_index.cgi?lang=eng.

[MOTOBALL]

The NIST website I quoted previously also has IR spectra for you to compare with your unknown; however, please try to interpret your IR before doing the visual comarison.