The Spectra of Propyl Benzoate

Propyl benzoate, also known as benzoic acid propyl ester, is a naturally-occurring chemical compound found in clove stems and sweet cherries. This organic compound is used in a number of applications.

It is characterized by a nutty odor and tastes like a sweet fruit, and hence used as a synthetic flavoring agent in foods. It also has antimicrobial properties and used as a preservative in the cosmetics industry.

To this end, Anasazi Instruments has developed an automated procedure for calibrating decoupler power and pulse widths. A 98% propyl benzoate/2% TMS sample is typically employed in this process.

Propyl Benzoate

In Figure 1, the proton spectrum shows the standard resolution of the EFT nuclear magnetic resonance (NMR) spectrometer even in case of a concentrated sample. Similar to esters, the alpha protons are transported to higher frequency because of the deshielding induced by the conjugation in the region of the ester functionality. The couplings of 1H-1H protons are suitably resolved for the aliphatic resonances.

Figure 1. Proton spectrum of 98% propyl benzoate with 2% TMS.

In Figure 2, the ¹³C spectrum was obtained in a minute and evidently resolves the 8 resonances. Both the single substituted ring carbon and the carbonyl carbon can be easily differentiated. These can be additionally improved by utilizing 30 degree pulse widths, rather than 90 degree pulse widths, and raising the relaxation delay by 1 to 2 seconds further than the standard.

Figure 2. C13 spectrum of propyl benzoate

The ¹³C DEPT experiment employed in the EFT spectrometer achieves DEPT135, DEPT90, and DEPT45 spectra. These spectra in turn are taken as one data set and processed automatically. Carbons without directly attached protons (1, 7) were not used in all the three experiments. In Figure 3, it can be seen that the DEPT-90 has virtually no remaining evidence of the CH3 or CH2 resonances.

Figure 3. C13 DEPT spectra for propyl benzoate

2D Experiments

COSY (Figure 4) and HETCOR or Heteronuclear Correlation (Figure 5) are 2D experiments that are often utilized on the EFT spectrometers. The COSY experiment employs gradient pulses that enable faster acquisitions sans complete phase cycling. This reduces the time taken for the experiment by a factor of 4.

Figure 4. COSY spectrum of propyl benzoate

Figure 5. HETCOR spectrum of propyl benzoate

The HETCOR experiment provides ¹H-¹³C coupling data for protons that are directly adhered to carbons. In the 2D plot, the peaks specify that the ¹³C above the peak is directly joined to the proton(s) to the left side of the peak.

Conclusion

Thus, Anasazi’s EFT NMR spectrometers can be effectively used for acquiring the spectra of organic lab products such as propyl benzoate.

About Anasazi Instruments

Anasazi Instruments has been providing high quality, rugged, easy-to-use 60 and 90 MHz NMR spectrometers and upgrades to the educational and industrial markets. These instruments have been successfully implemented at hundreds or institutions ranging from large companies and top-tier universities to community colleges throughout North and South America.

In research environments, the Eft is a cost-effective workhorse for synthetic and analytical laboratories. These permanent magnet based FT-NMR spectrometers have applications in industrial labs for quality testing or as a "walk-up" NMR resource. Crucial to the success of the Eft is that, over the lifetime of the instrument, the total annual cost is fixed, whereas for a supercon-based NMR, annual costs increase.

In education, the Eft gives thousands of undergraduates the hands-on opportunity to learn to acquire and analyze FT-NMR data. Additionally, the wide appeal of the Eft spectrometer is due to the ease of obtaining high quality NMR spectra on an instrument that does not required cryogens and has minimal maintenance requirements.

This information has been sourced, reviewed and adapted from materials provided by Anasazi Instruments.

For more information on this source, please visit Anasazi Instruments.