INDEX double-bond shift

NMR mass chromatogram corresponds to a one-dimensional UV or refractive index chromatogram. The second peak consists of methyl methacrylate and ethyl acrylate, which is evident from the different chemical shifts provided from the on-line experiment. A clear differentiation is available from the chemical shift of the methyl group of both compounds. The chemical shift at 1.9 ppm indicates the methyl group at the double bond of methyl methacrylate, whereas the signal at 1.22 ppm is from the terminal methyl group of ethyl acrylate. Thus, the second dimension of the SFC-NMR run, provided by the H chemical shifts, enables the separation of co-eluting compounds. 

Proton chemical shifts are also a potential index of aromaticity. Thus, in pyrazine 7 the protons resonate at S = 8.6 ppm, whereas in its antiaromatic 162 and nonaromatic 163 derivatives the double bond protons show signals at 4.64 and 5.38 ppm, respectively <1983AGE171>. There is qualitative agreement with the ring current influencing... 

Using the chemical shift information and the index of hydrogen deficiency, you should be able to determine that the unknown componnd contains a C=C—H and a COOH group by observing the peaks at 6.8 and 12.5 ppm. Since there is only one peak in the alkene region, you might suggest that the double bond is trisubstitnted. 

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