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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: adamalt on March 05, 2008, 10:14:34 AM

Title: Mass spactrum
Post by: adamalt on March 05, 2008, 10:14:34 AM

 What is tyhe strucutre of the compund of C10H12O that has e-impact mass spectrum m/e values of 15,43,105.148?

Title: Re: 13C NMR
Post by: ARGOS++ on March 05, 2008, 04:13:36 PM

Dear Adamalt;

Some combinations you can find on:   "AIST: Spectra-DataBase (http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi)”
(Enter your molecular formula & select your spectrum type.)



Good Luck!
                    ARGOS⁺⁺

Title: Re: 13C NMR
Post by: adamalt on March 06, 2008, 08:09:39 AM

But there are more then 20 of them how can I know which one is which?

Title: Re: 13C NMR
Post by: macman104 on March 06, 2008, 08:21:06 AM

When I looked for molecules of C10H12O and with the mass peaks of 15, 43, 105, 148, I got 24 hits.  That means that all of those compounds produced peaks of those values.  You're going to need more information if you want to figure out what compound you have.  Especially 15 and 43 are very common peaks.

Also, why did you label this topic as C13 NMR, this is Mass Spectrometry...

What compound do you think it is?

Title: Re: 13C NMR
Post by: ARGOS++ on March 06, 2008, 08:49:41 AM

Dear Macman104;

Why, you think, I wrote: “Some Combinations!” (Only!)?


Good Luck!
                    ARGOS⁺⁺

Title: Re: 13C NMR
Post by: macman104 on March 06, 2008, 09:12:59 AM

Quote from: ARGOS++ on March 06, 2008, 08:49:41 AM

Why, you think, I wrote: “Some Combinations!” (Only!)?

Oh, I realized that, I was responding to adamalt's question about which one was the "right" one.  Explaining why there were multiple matches...

Title: Mass spactrum
Post by: adamalt on March 06, 2008, 03:08:28 PM

But there is a big list of them are they all true? or does it have to be the same formula?

Title: Re: Mass spactrum
Post by: ARGOS++ on March 06, 2008, 03:20:04 PM

Dear Adamalt;

No – Not necessarily.
If you know other Mass-fragments, then you have a possibility to distinguish.
Otherwise a quite less secure method is to use the ratio of signal intensities to find possible candidates.

At least we need additional Infos.

Good Luck!
                    ARGOS⁺⁺

Title: Re: Mass spactrum
Post by: adamalt on March 06, 2008, 03:22:59 PM

This is the only information that Í have but I thought it has to be the same formula C10H12O

Title: Re: Mass spactrum
Post by: ARGOS++ on March 06, 2008, 03:49:33 PM

Dear Adamalt;

I think in this case we are also not able to distinguish, - Sorry!
(The WebBook knows at least 72 with the same C₁₀H₁₂O!  How we should?)
: ---->   "NIST Chemistry WebBook (http://webbook.nist.gov/chemistry/)”
              (Name or “Sum Formula” is possible.)


Good Luck!
                    ARGOS⁺⁺

Title: Re: Mass spactrum
Post by: azmanam on March 06, 2008, 04:35:50 PM

My guess is the provided peaks are intentional to allow the building of 'puzzle pieces' to form the molecule.

I contend we do have enough information.

True, SDBS gives a few dozen possible hits for those 4 fragment ions, but do you really expect all of those to fragment into fragment ions significant enough to warrant inclusion in a problem of this nature?

adamalt: are you familiar with Norrish processes and acylium ions in mass spec?

Here's what I see:  15 is a common ion indicating a particular functional group.  43+105 = 148.  C₁₀H₁₂O = 148 gmol^-1.  Given degrees of unsaturation, I can build a likely and plausible structure from this information.

(although I am surprised 91 wasn't thrown in with the given peaks...)

What say you?

(edited to clarify)

Title: Re: Mass spactrum
Post by: azmanam on March 06, 2008, 04:42:57 PM

FYI: 15, 43, and 91 are all very characteristic peaks which should get a student thinking about particular puzzle pieces immediately.

(with 43, watch out for McLafferty rearrangements (link (http://en.wikipedia.org/wiki/McLafferty_rearrangement))giving fragment ions of perhaps-not-predicted mass)

Title: Re: Mass spactrum
Post by: adamalt on March 07, 2008, 06:17:12 AM

I think 15 is CH3

Title: Re: Mass spactrum
Post by: azmanam on March 07, 2008, 06:18:40 AM

Quote

I think 15 is CH3

True.

Do you know what 43 is?  91 may not be as obvious, but when you figure it out, I think you'll see why it is common.