ACech2

=C NMR=

Experiment 59 involves the synthesis of a Ugi from 5-methylfurfurylamine, Boc-Gly-OH, t-butyl isocyanide, and piperonal. C NMR of the reactants reveal information about the structures of the molecules. In general, carbon chemical shifts are about 15 to 20 times greater than the corresponding proton chemical shifts. Off-resonance decoupling allows the identification of protons attached to the carbon atom.

The C NMR of piperonal and 5-methylfurfurylamine are analyzed below.

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 * Piperonal (1,3-benzenodioxole-5-carbaldehyde)

The C=O double bond can be found in the range from 165 to 210 ppm. The C=O bond in this molecule shows up at about 190 ppm. A C-O single bond lies between 55 and 90 ppm and can be found for piperonal at about 78 ppm. The remaining carbons in the piperonal molecule are part of a benzene ring. Aromatic carbons have a chemical shift of 115 to 150 ppm. As can be seen below, there are numerous peaks that fall in this range. It can be expected that the carbons bonded to the oxygen atoms have a stronger chemical shift due to the electronegativity of the oxygen. The peaks for these two carbons could fall in the 145 to 160 ppm range. The carbon attached to the carbonyl group would also have a greater chemical shift, and could be estimated to be in a range from 120 to 135 ppm.




 * 5-methylfurfurylamine ((5-methyl-2-furyl)methylamine)**

5-methylfurfurylamine also contains both C=C double bonds and C-O bonds. As in piperonal, the two carbons attached to the oxygen in the 5-methylfurfurylamine molecule could fall in the 145 to 160 ppm range. The carbon in the methyl group falls within the alkane chemical shift range of 0 to 35 ppm. A peak at 14 ppm can be seen below. Alkenes have C NMR shifts between 100 and 150 ppm. The two alkene carbons have peaks at about 106 ppm. C-N bonds can have a chemical shift between 45 and 55 ppm. This shift is greater in the 5-methylfurfurylamine molecule because the carbon is attached to another carbon with a C=C and a C-O bond. A peak can be seen at 78 ppm.