Experiment designed to illustrate the quantitative relationship between an easily measurable property (amide proton NMR chemical shift) and the electronic effect of several different substituents on substituted benzanilides; includes sample data and analysis.
The propoxylation of lactose (a dairy waste by‐product), under basic conditions, yields polyether polyols that have been found to be a good substitute for sucrose polyether polyols currently used in the rigid polyurethane foam industry. 13C‐NMR analysis of polyethers of sugars indicate that while the disaccharide α (1 → 2′) linkage of sucrose remains intact during propoxylation, that of lactose breaks, giving polyethers of monosaccharides. In addition, IR spectra reveal the absence of unsaturation in the product. The presence of multiplicities of the different carbon peaks of propylene oxide in the NMR spectrum of the product implies a regioselective attack on the C‐1 or C‐2 of propylene oxide by the incoming nucleophile.
To obtain the optical purity of a sample using polarimetry requires the value of the absolute rotation of the pure enantiomer. However, this is a condition that cannot always be met. The separation of a racemic mixture into its constituent enantiomers (i.e., resolution or optical resolution) and the determination of the optical purity of the resolved material has therefore provided a challenge for chemists. The problem is acute because the 20.0 15.0 10.0 PPH -r " o.o only differences between enantiomeric Figure 1.200 MHz 1H-NMR spectrum of the chiral LSR-Yb(TFC)3 in CDCI3.pairs can be subtle. In contrast, diastereomers (i.e., stereoisomers that are not enantiomers) are distinguishable even in achiral surroundings and exhibit different physical properties, for example, melting point, solubility, and IR and NMR spectra. It thus seems logical that most methods of resolution in-volve the conversion of enantiomers into diastereomers (1).
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