Explain how the “CORN” rule can be used to identify an enantiomer of alanine as either $\mathrm{D}-$ or $\mathrm{L}-$alanine.

The structures of vitamin $\mathrm{C}$ and the preservatives $2-\mathrm{BHA}$ and $\mathrm{BHT}$ are shown in figure $17$.

Determine any chiral carbon atoms in these three compounds by placing an asterisk, *, beside them on a copy of the figure.

The monosaccharide $\mathrm{D}-$fructose is sweeter than $\mathrm{D}-$glucose, so it can be used in smaller amounts in foods. Identify the stereoisomer ($\mathrm{\alpha }-$ or $\mathrm{\beta }-$) of the cyclic forms of glucose and fructose in figure $18$.