The Spectra of trans-Ethyl Crotonate

One of the components of aroma products is ethyl crotonate, trans- (ethyl but-2-enoate). This organic chemical compound is highly flammable and does not dissolve in water. The clear, colorless liquid has a pungent odor. A 5% solution of ethyl crotonate sample in CDCl3 is used by Anasazi Instruments as a line shape standard.

Spectra of Ethyl Crotonate Sample

The proton spectrum of a 5% ethyl crotonate dissolved in CDCl3 is presented in Figure 1, revealing the ultimate resolution capability of the EFT 60/90 spectrometers. In all of the peaks, the 1H-1H proton coupling is observed. The residual CHCl3 in the solvent is observed in the proximity of the high frequency doublet of quartets.

Proton spectrum of 5% Ethyl crotonate in CDCl3

Figure 1. Proton spectrum of 5% Ethyl crotonate in CDCl3

The BAPR technique was used to acquire the 13C and DEPT spectra for the 5% ethyl crotonate sample (Figure 2), enabling extended data collection on diluted samples without using a field frequency lock. The six resonances as well as the TMS are easily resolved by the 13C spectrum (maroon). The solvent triplet for the CDCl3 can also be observed.

DEPT (top) and C13 (bottom) spectra of 5% Ethyl crotonate in CDCl3

Figure 2. DEPT (top) and C13 (bottom) spectra of 5% Ethyl crotonate in CDCl3

Carbons with directly attached protons are typically much larger than those without directly bonded protons(C4 carbonyl). These can be improved through the use of 30°+ widths in place of 90° and extending the relaxation delay by 1-2 seconds in excess of the standard. As a result, the carbonyl can be observed even with the application of standard acquisition parameters.

The DEPT-135 spectrum clearly shows the single CH2, two methynes and two methyl peaks. As anticipated, the solvent peaks and the carbonyl carbon are quenched due to the absence of directly attached protons.

Heteronuclear Correlation

Unlike the COSY experiment, the Heteronuclear Correlation (HETCOR) experiment considers coupling between two different nuclei types. Using the HETCOR experiment, proton resonances are correlated with those of directly attached carbon-13 or other nuclei. The proton is represented by the axes of the contour plot.

Other X-nucleus chemical shift ranges and signals take place at coordinates relative to the shifts of the bonded pairs of nuclei. This experiment detects X-nucleus signals rather than those of the protons. Long range coupling information (couplings between X-nucleus and proton through 2-3 bonds) can be obtained by modifying the delays in HETCOR. Figure 3 shows the HETCOR spectrum for the 5% ethyl crotonate in CDCl3.

C13-H1 Heteronuclear Correlation (HETCOR) of 5% Ethyl crotonate in CDCl3.

Figure 3. C13-H1 Heteronuclear Correlation (HETCOR) of 5% Ethyl crotonate in CDCl3.

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.

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