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Ethyl Crotonate

Ethyl Crotonate

trans -ethyl crotonate is often used to illustrate NMR spectroscopic experiments. The molecule is historically chosen specifically for its simplicity so that the elegance of the NMR spectra might be clearly demonstrated.

Data Collection

Bruker AVIIIHD500 FT-NMR spectrometer

5 mm SMART probe

1D proton NMR spectrum. 1D proton spectra are typically acquired within minutes. The signals are integrated to show the relative ratio of proton signals in each chemical environment and the peak multiplicities can show the coupling network within the molecule.

1D carbon NMR spectrum. 1D carbon spectra are normally acquired with BB proton decoupling to simplify the spectrum by removing all proton couplings. However, this simplification comes at the cost of losing carbon multiplicity information.

1D carbon NMR spectrum. The UDEFT (uniform driven equilibrium fourier transformation) pulse sequence can be used to acquire 13C NMR spectra with enhanced quaternary carbon signals by forcing faster relaxation.

The dept135 spectrum is a spectral editing technique used to differentiate different types of carbon within the structure, regaining the information lost by BB decoupling; the illustrated spectrum is phased such that CH/CH3 signals are positive and CH2 signals are negative (quaternary carbons are om

1D carbon (dept135) NMR spectrum. The dept90 spectrum is a spectral editing technique used to identify methine (CH) carbons. Signals from CH2 and CH3 may also be present but they will be heavily attenuated; quaternary carbons will be omitted.

The Jmod spectrum is another spectral editing technique used to differentiate different types of carbon within the structure; the illustrated spectrum is phased such that CH/CH3 signals are positive and C/CH2 signals are negative

HH COSY. The HH COSY shows the coupling network within the molecule: the triplet and quartet of the ethyl group share a crosspeak; the alkene protons can be seen to couple to both each another and the terminal methyl group.

HSQC. In the HSQC spectrum the one-bond direct HC couplings can be viewed as cross-peaks between the proton and carbon projections; in the illustrated spectrum, DEPT editing has been applied.

HMBC. In the HMBC spectrum the two- and three- bond couplings between protons and carbons can be seen as cross-peaks.

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