[sule21]

i need help determining an unknown:

here is the key raw data:

melting point = ~ 172*C

NMR peaks at:

7.281 (single peak)
~ 3.4 (doublet)
3.5, 3.7 (triplets)

*its an acid (likely a carboxylic acid)

mass spec major peaks at:
99, 72, 55, 45

highest given peak = 116 (not a high peak)
lowest given peak = 29 (not a high peak)

m/z = 116

my original thought was this was hydroquinone, but apparently its not an aromatic

help please

[Dan]

Do you have the integration for the nmr peaks?
How do you know it's an acid?
Any IR data?

[chiralic]

Hello sule21:

Look at on these links:

http://www.colby.edu/chemistry/NMR/NMR.html

http://www.colby.edu/chemistry/PChem/Formula.html

NMR: Absorption 7.281 (single peak) must be considered:
- Possibility of aromatic proton  or
- groups of CHO, OH, COOH

The splitting on:
- 3.4 (doublet)  must be: (CH3)2CH group or CH3CH group
- 3.5 ; 3.7 (triplet) must be: C2H5 group or CH3CH2CH2 group

MS: What is the Ion base?

From you mass spect I get the following info peak=29 must be CHO or CH2CH3 (also NH2 or CH3N)
and your peak=116 maybe considered your Molecular Ion =>The molecular weight

As said Dan, Do you have IR data? Do you have the integration of peaks?

Regards,

Chiralic

[AWK]

Hello sule21:

Look at on these links:

http://www.colby.edu/chemistry/NMR/NMR.html

http://www.colby.edu/chemistry/PChem/Formula.html

NMR: Absorption 7.281 (single peak) must be considered:
- Possibility of aromatic proton  or
- groups of CHO, OH, COOH

The splitting on:
- 3.4 (doublet)  must be: (CH3)2CH group or CH3CH group
- 3.5 ; 3.7 (triplet) must be: C2H5 group or CH3CH2CH2 group

MS: What is the Ion base?

From you mass spect I get the following info peak=29 must be CHO or CH2CH3 (also NH2 or CH3N)
and your peak=116 maybe considered your Molecular Ion =>The molecular weight

As said Dan, Do you have IR data? Do you have the integration of peaks?

Regards,

Chiralic

There are no NMR data for CH3 group bonded to C atom

[Custos]

Do you have any more information? If the molecular weight is 116, the peak at 99 is loss of OH and the peak at 116 is loss of CO₂ (decarboxylation of the acid) so that fits. The NMR data is puzzling - are you sure it's correct (peak integration would be helpful). The singlet at 7.2 sounds a bit like a vinyl proton but I can't figure out how to get two triplets and a doublet with the remaining molecular weight. The closest I got was the attached which would have the two triplets at around the right spots, the singlet at 7.2, but the molecular weight is short by 2 and no doublet. 

[Borek]

and the peak at 116 is loss of CO₂ (decarboxylation of the acid)

You mean 72 probably?

[mibs]

Hi!

Right, where to begin...

An mp of 172C is quite high, implying H-bonding, but the nmr doesn't seem to support this conclusively.

Is the H-NMR run in CDCl3? Because that would explain your peak at 7.28 - residual CHCl3 peak.

About your MS... what ionisation was it? I'm assuming EI or ESI, but do you have Na+ or K+ present? because you might be observing [M+Na] or [M+K] in addition to your [M+H] peak.

With regards to Chiralic...

NMR: Absorption 7.281 (single peak) must be considered:
- Possibility of aromatic proton  or
- groups of CHO, OH, COOH

aldehyde protons tend to exhibit around 9-10ppm
COOH protons are anywhere between 10-12ppm depending on solvent.

If the nmr solvent is able to exchange protons with any of these, you shouldn't observe them.

And OH protons in alcohols are around 5ppm.

Also:

The splitting on:
- 3.4 (doublet)  must be: (CH3)2CH group or CH3CH group
- 3.5 ; 3.7 (triplet) must be: C2H5 group or CH3CH2CH2 group

If your NMR data is complete, then (CH3)2CH and CH3CH-R2 are unlikely as you would observe a doublet/septet and doublet/quartet respectively.

It's an interesting question, a little more info would probably sort things out.

Happy reactions,
mib

[Dan]

Is the H-NMR run in CDCl3? Because that would explain your peak at 7.28 - residual CHCl3 peak.

Hahaha, I completely missed that, good call!

[chiralic]

Hello everynoe:

I offer my apologies related with my wrong interpretation of NMR absorptions. It was a "lapsus calami"
when I read a Flow Chart from Journal of Chemical Education Interpreting Infrared and Nuclear Magnetic Resonance Spectra of Simple Organic Compunds.

Regards,

Chiralic