Ibuprofen
Ibuprofen is a nonsteroidal anti-inflammatory agent and the active ingredient in a number of over the counter pain relievers, e.g. Advil, Motrin, and Nuprin. It is one of the top-ten drugs sold worldwide. Although it has been shown that only the S enantiomer has the desired biological activity, it is currently sold as the racemate.
Also known as (±)-2-(p-isobutylphenyl) propionic acid, it takes the form of a white powder with a melting point of 74°-77°C. It is very slightly soluble in water (<1 mg/ml), but readily soluble in organic solvents such as ethanol and acetone.
Here, multiple experiments help to determine the spectral details of ibuprofen. In this sample, multiple dimension (2D) experiments are needed to interpret anomalies in the 1D spectra.
Concentration: 2 M in CDCl3
1D proton spectrum
Data acquired in about 11 seconds.
The peak near 12 ppm is the carboxylic acid
13C Spectrum
Data acquired and processed in about 3.5 minutes.
The number of resonance lines seems to be less than expected
13C DEPT spectra
All data acquired and processed in under 11 minutes.
From top to bottom: DEPT-135, DEPT-90 and DEPT-45.
Carbons without directly attached protons do not show up.
All three are acquired and processed as a single experiment.
In the DEPT-45 (bottom), all resonances are positive, In the DEPT-90 (middle), only CH (methyne) peaks are present and point positive. Finally, in the DEPT-135 (top), CH and CH3 (methyl) peaks are positive while CH2 (methylene) peaks point negative.
In this sample, a CH and CH2 appear at the same frequency (45 ppm). These two superimposed resonances lead to the unexpected result of a null in the DEPT-135 where one would expect to see both the CH and CH2 lines appear. This same phenomenon is seen on a 600 MHz carbon spectrum of ibuprofen. (Spectrum taken on a JEOL 600MHz spectrometer at the University of the Pacific in Stockton, California)
13C HETCOR Spectrum
Data acquired and processed in under 9 minutes.
Confirmation of structure from 1H, 13C and DEPT experiments.
Here we see the problem that the DEPT experiment could not contend with; the two carbons with identical 13C chemical shifts at 44.8ppm are resolved because they are bonded to protons with different chemical shifts (3.67 and 2.48). One can further determine that they are CH and CH2 resonances from the integration of the proton spectrum on the vertical axis.