HNMR Spectra of Ethanal from http://science.widener.edu/svb/nmr/known_jdx.html.
Molecular Formula for Ethanal: CH3CHO
Image_Ethanal.JPG
Structure of Ethanal




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Fig. 1 - Complete HNMR Spectrum of Ethanal

This is the complete spectrum of ethanal. The signal at 0.0 corresponds to the compound added to the sample to define zero. Usually this compound is tetramethylsilane (TMS) because. Since silicon is less electronegative than carbon, TMS protons are highly shielded, allowing the signal to be http://www.wikispaces.com/_/2009030201/i/c.gifdefined as zero. Organic protons absorb downfield (to the left) of the TMS signal. Therefore, the other two signals correspond to the two different types of protons present in ethanal. The molecular formula for ethanal is CH3CHO. The three protons on the carbon are all the same, so the other type of proton is the one connected to the C=O. The larger signal (signal 1) around 1.50 indicates that there are more protons of that sort than there are of the shorter signal (signal 2)just above 9.0.

*The two signals are numbered 1 and 2 just to clarify what zoomed in picture they correspond to below. These numbers have no bearing on the analysis of the spectrum.
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Fig. 2 - Detailed View of Signal 1

This picture takes a closer look at the larger signal (signal 1) from the picture above. The location of this signal (around 1.65 ppm) indicates that is it highly shielded. Of the two types of protons in ethanal discussed above, the protons on the first carbon (the carbon not bonded to the oxygen) are more shielded than the protons on the carbon double bonded to the oxygen. This signifies that this signal correlates to the protons on the -CH3 of ethanal. This peak also has two peaks that fulfill the requirements for being a doublet because the ratio of the area under the peaks is 1:1. According to the N + 1 rule, this tells us that there is only one proton on the carbon next to the carbon that has these protons. This is accurate and confirms that this signal corresponds to the proton in CH3 because on the carbon adjacent to this carbon there is only one proton. All of the protons on the –CH3 are identical and identical protons do not split each other. Therefore there are only two peaks.


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Fig. 3 - Detailed View of Signal 2

This picture takes a closer look at the smaller signal (signal 2) from the picture above. The location of this signal (around 9.33 ppm) indicates that the protons are much less shielded than the protons of the previous signal. As determined before, this signal must have fewer protons than the more shielded signal because it is shorter. Since there are only two types of protons in ethanal and from the picture above it was determined that the more shielded signal correlated to the protons on -CH3, this signal must correspond to the proton on the -CHO portion of the molecule. This proton is bonded to the carbon that is also double bonded to oxygen, making the proton very deshielded. This tells us why the signal for this proton is more downfield than the signal for the other protons. This signal has four peaks, meaning that on the carbon next to the carbon this proton is on, there are three protons. And, indeed, there are three protons because the other portion of the molecule is –CH3. These four peaks are a quartet because the area under them (1:3:3:1) matches with the expected area for a quartet. This is accurate and confirms that this signal corresponds to the proton in -CH3 because on the carbon adjacent to this carbon there is only one proton.

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