Automated identification of monoalkenes by 13C NMR
1973 Volume 22 Issue 4 Pages 399-404
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1973 Volume 22 Issue 4 Pages 399-404
The automated chemical structure analysis of organic compounds has attracted much recent interest. In this paper, the identification of monoalkenes by a computer aided-13C NMR spectrometry is reported as a link of our work op automated analysis. The computation for the identification of monoalkenes is carried out along the flowdiagram shown in Fig. 1 by feeding the molecular formula, the 1H NMR spectrum, and the complete proton decoupling 13C NMR spectrum of a certain sample of monoalkene as input. First, all probable structural and geometric isomers are constructed based on the molecular formula and the components (Tables II and III) designated by the 1H NMR analysis. Then the chemical shift of each carbon in every structure is computed by using both the 13C-chemical shift prediction parameters of Lindeman and Adams for alkanes and our correction parameters for α-, γ- and trigonal carbons of alkenes (Table IV, V and VI). Finally, the structure whose predicted spectrum is consistent with that of the sample within the limit of ± 5 ppm is typed out as the most likely candidate.
The structure identification of an unknown sample whose 13C NMR spectrum is 180.10, 180.00, 171.10, 164.30, 69.70 and 62.80 is explained as an example. The components, CH=, C, CH, CH2, CH3, DCH3, and DRH are designated for this sample by the 1H NMR analysis (Tables VII and VIII). Here, DCH3 and DRH express C=CCH3 and the number of hydrogens attached to α-carbon of olefinic linkage, respectively. Then four probable structures, STRUCTURE(1)(4), are constructed based on the molecular formula, C6H12, and these components. The predicted spectra for these four structures by an aid of both Lindeman'sparameters and the parameters of Tables IV, V and VI, are as follows:
STRUCTURE (1)
5 CH3 178.94-3 CH2 172.95-1CH 61.95=2 CH 61.95-4 CH2 172.95-6 CH3 178.94
STRUCTURE (2)
5 CH3 178.94-3CH2 167.45-1 C H 61.25=H C 2 61.25-4 CH2 167.45-6 CH3 178.94
STRUCTURE (3)
6 CH3179.94-4 CH2 170.15-3 CH2 164.05-1 C H 61.95=2 C H 69.75-5 CH3 181.14
STRUCTURE (4)
6 CH3 179.94-4 CH2 170.15-3 CH2 158.35-1 C H 61.25=H C 2 69.05-5 CH3 175.94
By comparing the predicted spectra of STRUCTURE, (1)(4) with the observed spectrum, it can be suggested that the STRUCTURE (3), cis-hexene-2, is the most plausible structure for this sample.
The above-mentioned computation system has been applied to more than twenty monoalkenes, and all the results obtained are satisfactory(Table IX).
