[giosoton]

Hey, I'm new to this forum, so if this in the wrong place please move it.

So I have this NMR, with no molecule to compare it to, I've assigned most of the peaks, except for one cluster.
I'm not sure if it's a quintet or a multiplet, it looks too clear to be a multiplet so I'm assuming quintet. It's around 6.50ppm if that helps. The integration comes out as 3.
The molecule is C12H12O4 with a conjugated carbonyl.

There are other peaks, a triplet J=9.0 with integration of 3, which I'm certain is a methyl 1.85ppm
                               a quartet J=9.0, integration 2, I guess a methylene 4.27ppm group connected to the methyl
                               a singlet, integration 2, which I'm not sure about yet 5.90ppm
                               a doublet, J=24 integration 1, 7.70ppm
                               finally another doublet J=24 integration 1. 6.25ppm

I know this must be hard to do without a copy but I'm really stuck.

[plankk]

Looking at molecule's formula and your peaks I assume that you've got a benzene derivative and your undefined cluster comes from benzene ring.

[ramik]

Hi
attach a copy of the molecule, and I'll give you the answer

[giosoton]

Hi
attach a copy of the molecule, and I'll give you the answer

Sorry, I can't it's undefined, I have to work out the structure from the NMR. Which is why I'm having such problems.

[Arctic-Nation]

Just spent half an hour trying to figure this one out, to no avail. My main trains of thought were some ethylene derivative or a benzofuran, but I never could reconcile chemical shifts and integrations. The only thing I'm sure of is the presence of an ethyl ester.

Do you have any additional information, such as whether certain peaks are broad, or, if you're in a lab, a mass spectrum?

[alphahydroxy]

From the information you have given, I would suggest that it is ethyl cinnamate (see pic), although the actual values of the coupling constants and shifts from this molecule (in CDCl₃) are different...

Also, can you elaborate on what you mean by:

"I'm not sure if it's a quintet or a multiplet, it looks too clear to be a multiplet so I'm assuming quintet."

It is either a quintet or it isn't - a quintet will have the correct relative intensities for the peaks, and will also have a uniform coupling constant. The problems begin when the signal is broad or obscured in the spectrum...

[azmanam]

I would suggest that it is ethyl cinnamate

That was my first thought, too.  But thats only 11 carbon atoms and two oxygen atoms.  Just so we're on the same page op, does the NMR look like what Ive shown below (http://www.nmrdb.org/resurector and http://www.nmrdb.org/predictor are the awesome-est websites evah).

My guess also contains an ethyl cinnamate, but has a carboxylic acid ortho or meta to the 'cinnamate' part.  That'll get the molecular formula right, and might not add any peaks to the NMR if the acid at 10-12 ppm doesn't grow in (quite likely).  I say not para, because para substituted benzene rings have clean and predictable NMR splitting patterns that are two sets of doublets, not multiplets.

Below are three NMR.  The first is what I hope your NMR looks like.  The second and third are my two guesses.  Note they're not the same.  this is not necessarily bad.  This could mean the predictor is wrong (likely).  But at least it gives us a starting point.

giosoton - can you give us any more information? anything?  did you make this? if so, what was the reaction/ reaction conditions.  Did you do any other qualitative or quantitative analysis (IR? TLC? mass spec? distillation? column chromatography?) What was the context in which you were told to analyze this NMR? (in lecture during the class on carboxylic acids? In lab during the Wittig week? At home because you're a citizen chemist?)  HELP US HELP YOU

The only problem is that means the 'undefined cluster' for the aromatic peaks should a) be above 7 ppm and b) integrate to 4 protons.

[azmanam]

ok, new guess.  After posting, I noticed the sharp singlet at 5.9 in the op's NMR that is missing from  my guesses. That really threw me off, because I couldn't figure out how else to get two more oxygen atoms and one more carbon atom while fulfilling the other requirements.

Then I had a vision. Not kidding, I blacked out for a few minutes, and when I came to, I saw this shape in my head.  Ok, I am kidding, but this is my new guess.  It's the closest I can get to fulfilling all the requirements.  I like the first one better.  In the second one, the isolated aromatic proton (if not under the multiplet) would be a singlet.  In the first one, the three multiplets would all split each other and lead to a more multiplet-type scenario.  Would still love more info, op.

(I don't know why the predictor is predicting the acetal protons are a doublet.  The molecule is achiral, so I'd suspect they'd coalesce into a singlet in real life and not be split by anything.)

[sjb]

(I don't know why the predictor is predicting the acetal protons are a doublet.  The molecule is achiral, so I'd suspect they'd coalesce into a singlet in real life and not be split by anything.)

Could it be the (Z) alkene, especially with the large J value, then you've possibly got restricted rotation to an extent at the dioxolane, and so two different proton environments? Don't have a molecular modelling package to hand here...