A student found a reaction flask filled with solution sitting on a lab bench near an empty bottle of sodium hydroxide (NaOH) and decided to characterize the products. The student purified the sample and characterized it using nuclear magnetic resonance (1H-NMR). Further analysis showed the presence of four compounds, shown below:
The NMR for the entire mixture is shown here. The chemical shift (δ) is graphed on the x-axis in parts per million (PPM), relative to the chemical shift of tetramethylsilane, (CH3)4Si, as a standard (not shown). The y-axis shows intensity. The chemical shift describes the electronic state of the region around the hydrogen. Hydrogen with very low chemical shifts, typically those on alkane chains, have large electron densities that “”shield”” the hydrogen nuclei from the magnetic field produced by the scanner. Hydrogen that are higher on the chemical shift scale are referred to as “”deshielded”” and contain electronegative groups, double and triple bonds, and aromatic groups nearby that effectively pull electrons away from those particular hydrogen.
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