[zeshkani]

 hi there, well ill be running an experiment next week and its a maybe a soild or liquid and iam supposed to figure out the structure of the compound, and this will be my procedure, maybe if you guys have some thoughts or ideas if i should do something different or, and i only have 6 hours in the lab to figure out the structure

1. Get IR spectra, see if there are any carbonyl groups, alcohols, and aromatic rings
2. If unknown is liquid, get NMR for hydrogen and also Carbon, this can give me the number of Carbons ?
3. i dont know, should i run Mass spec.
4. if solid get melting point, if liquid get micro-melting point.
5. if liquid run a GS, i dont know what this will help me at ?
6.  if carbonyl group present, test with NaCo3 for carboxylic acid, and to other test if not carboxylic acid
7. are there any suggestions on what else i can do, to figure out the stracture ?

any help is welcome thanks

[Ψ×Ψ]

If solid, you can dissolve in CDCl₃ (or another handy deuterated solvent) and get NMR.  Even if it's a neat liquid, it's probably a good idea to throw a little chloroform-d in there.  Else, you can get crazy splittings in the peaks because of coupling between adjacent molecules.  (That might not be quite the right explanation, but I think it's the one I was given.  Happened to me in an "ID-the-unknown" class once upon a time.)

[Sam (NG)]

I'm not sure that you can get the number of Carbons from the nmr.  Mass Spec is always useful, but do you have the time to do all these things....?

[Dan]

I'm not sure that you can get the number of Carbons from the nmr.  Mass Spec is always useful, but do you have the time to do all these things....?

¹³C nmr will give you the number of carbon environments, which may or may not be the total number of carbons - MS will help clear that up.

I would certainly get ¹H and ¹³C (solution) nmr, MS, IR and melting/boiling point.
If possible/necessary, get DEPT, HMQC and COSY nmr spectra too. Maybe an HMBC if you're still stuck. A UV spectrum may also help.
Getting the data in under 6hrs will depend on the resources available and the competition for them. For example, if you have one nmr spectrometer between 30 people you will probably have to settle for just ¹H and ¹³C nmr.

[zeshkani]

these are the things that iam allowed to do, get NMR anykind, IR and Mass spec, and also any kind of experimentation, like for testing for aromatic rings, and alcohols, and all those other things

but thanks for all the replys

[Yggdrasil]

You could probably use the chemical testing to confirm some of the results from the spectroscopy.   For example, if your IR shows a carbonyl, you could do chemical tests to confirm which type of carbonyl (aldehyde v. acid v. ester v. ketone).  If you see evidence of an alkene, you should test that too (especially to distinguish between aromatic carbons and alkene carbons).  This information, you could also find out by spectroscopy, but sometimes its nice to have other data to help remove ambiguities in the spectra.

[Custos]

If the compound is not too complex you should be able to get the structure from N and C NMR, IR, and MS... perhaps with a few chemical tests to confirm.

In the Mass Spec, look for isotope patterns (molecular mass with a 3:1 pattern 2 units apart means a Chlorine, a 1:1 pattern 2 units apart means a Bromine). An odd molecular mass means an odd number of nitrogens.

Look at the carbon nmr to get an idea of how many and what type of carbons (beware that symmetry can mean 2 or more carbons can appear at the same resonance, and some carbons are very small or lost if they have poor relaxation). Looking at the carbon and proton nmr spectra together can usually give you most of the information about the carbon skeleton, when related back to the MS info above.

The IR will, as you say, indicate carbonyls, -OH and aromatics (although aromatics should be obvious from the carbon/proton nmr).

Putting all this information together is then a fun puzzle to solve.

[zeshkani]

here is what i got for the experiment today since i ran it today
-Melting point 159 -165C
- Nice sweet smell/ Soild, white color
- Dissolves in water easy
- very acidic pH around 2
The IR had a carbonyl group, more likely ester, but it also had an primary amine, here are the IR and NMR
anybody that can help, is welcome to

[Dan]

Unfortunately, it looks like your sample was too small for 13C nmr. I think you have a spectrum of chloroform and acetone. Did you get a 1H?

[Sam (NG)]

My guess from the IR and melting point is Salicylic Acid (http://en.wikipedia.org/wiki/Salicylic_acid),  with the two peaks above 3000 wavenumbers for the two OH groups.  The only thing that puts me off of this is that the carbonyl peak should be more 1690 than 1715 but i would still guess at that from the pH, mpt and IR.

[edit]  How did you run the IR? (solvent? mull?)

[zeshkani]

i dout  it has OH, since from the IR the two sharp peaks must be an amine, and yes it acidic around pH of 2, since litmus paper turned purple, and the IR was runned normally without anything, ill have Hyrdogen NMR and Mass Spec tommorow

[Sam (NG)]

i dout  it has OH, since from the IR the two sharp peaks must be an amine, and yes it acidic around pH of 2, since litmus paper turned purple, and the IR was runned normally without anything, ill have Hyrdogen NMR and Mass Spec tommorow

Would you not expect a primary amine to have a high pH?

How do you prepare solid phase samples for IR spectroscopy (i'm only used to dissolving them in organic solvents or creating a Nujol mull and using KBr cells, i'm genuinely interested)?

[Dan]

it acidic around pH of 2, since litmus paper turned purple,

I thought litmus was purple at neutral pH, red at pH <4, blue at pH >8.
Are you sure its acidic?

You should get another 13C nmr if you can. The sample size you need depends on the spectrometer, but 40 mg sould give you a spectrum.

[Yggdrasil]

Also, be sure to get a ¹H-NMR spectrum.  Since the abundance of ¹³C in your sample is very low, it can sometimes be hard to get a carbon-NMR spectrum of a sample that is in very low amounts/has a very low solubility.  However, ¹H nuclei are extremely abundant so getting a good signal from for a proton NMR is much easier and can be done even when your sample isn't concentrated enough to give you a good carbon NMR spectrum.

[zeshkani]

ill post the proton NMR tonight since iam running the experiment in about 3 hours from now, and ill get the Mass spec also.