NMR/Mass Spec Orgo Lab Question Please Help

[DrJ2B]

Hey all!

I am in the terrible predicament in my senior year because I have waited 2 years to take Orgo Lab 2. I have an NMR/Mass Spec question that I cannot figure out. My prof barely covered mass spec so I am not sure how to go about doing it. I have to determine the structure of the compound with the following data:

7.5 ppm multiplet 3H, 3.5ppm quartet 1H, 2.0ppm singlet 3H, 1.0 ppm doublet 3H, Mass Spectrum M+= 304/308 ratio 1:1, and IR Peak at 1700cm-1


I know the compound must have 9 hydrogens and contains at least one carbonyl group, but I am not sure how to go on. I would really appreciate any help. Thanks so much in advance.

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[DrJ2B]

oops I mean 10 hydrogens!

 

[podany24]

Any more info? Any oxygens?

 

[DrJ2B]

That is all the information given. Yeah, I was wondering about that too. Thanks for the help.

 

[trying]

sounds like a benzene ring with a carbonyl sticking off it or attached to an alkane branching from the ring

 

[DrJ2B]

Thanks so much trying and podany24! I am not sure what the M+ 304/308 ratio 1:1 is. I am thinking the 304 and 308 are the 2 different molecular weights perhaps dealing with isotopes of halogens or other elements. I think the 1:1 means their relative abundances which means that the molecular weight should be around 306. Can anyone confirm this? I am just thinking this all through and that makes the most sense to me.

 

[podany24]

Most likely the two MW refer to two different Hydration states. But without more info I cant go anywhere with this. Would need some carbon info to go any further.

 

[ChE_Babe]

These are both databases that are very helpful. You can search using a variety of criteria and they'll shoot back compounds that match. I used them as a check when identifying compounds, because once you have it narrowed down finding matching spectra is very reassuring!


This one has pictures of NMR/IR and is my favorite:
http://www.aist.go.jp/RIODB/SDBS/sdbs/owa/sdbs_sea.cre_frame_sea


This database has only organics compounds and has more limited spectra information, but can be helpful nonetheless:
http://www.colby.edu/chemistry/cmp/cmp.html

 

[DrWorkNeverDone]

is there a halogen present? it is way too high a number to be simply a hydrocarbon with a carbonyl....the 3H on the NMR at 7.5 suggests a trisubs. benzene...but since you only have three different signals that means that all the subs must be the same...i was thinking that the subs were 3 carbons with the middle being a carbonyl but things are not adding up right...usually in my class we dont talk about beyond 156 and around there.....so does that mean that 304 and 308 would act like a bromide? remember that the 1 to 1 means that the signals are equal....but im not sure if it accounts for things more than 2 steps away from one another...hope this helps.

 

[usmaple]

Well, here are a few guesses:

-the 7.5 3H is most likely a trisubstituted benzene ring
-the singlet with 3H could mean there's a -COCH3 attached to the ring (i.e. a carbonyl carbon directly attached to the ring with an alkyl group attached to the carbonyl carbon).
-the 1H quartet at 3.5 and the 3H doublet could be a -CHX-CH3 attached to the ring
-1:1 is usually Br, but that would be separated by 2 mass units. Is it possible there's actually a 306 peak as well, in a 1:2:1 (304:306:308)? That would mean 2 Br's, so both the 3rd substitution and the X in -CHX-CH3 could be Br.

So a trisub benzene ring with -Br, -COCH3, and -CHBr-CH3 attached in some orientation (I think you would determine it from the actual pattern in the 7.5 range), which would have 10 H's and a MW of 306. I'm not 100% sure on it, but you could check the calc's and draw it out to make sure everything fits in.