\(D\) and \(L\) notations can be used to describe the configuration of  carbohydrates and amino acids, so it is important to learn what \(D\) and \(L\) signify. In Fischer projections of monosaccharides, the carbonyl group is  always placed on top (in the case of aldoses) or as close to the top as possible  (in the case of ketoses). From its structure, you can see that . galactose has  four chirality centers \((C-2, C-3, C-4,\) and \(C-5)\). If the \(OH\) group attached  to the bottom-most chirality center (the second from the left, the compound is  an \(L\)-sugar. Almost all sugars found in nature are \(D\) -sugars. Notice that the  mirror image of a \(D\) -sugar is an \(L\) -sugar. 

\(D\) and \(L\), like \(R\) and \(S\), indicate the configuration of a chirality center,  but they do not indicate whether the compound rotates plane-polarized light to  the right \((+)\) or levorotatory. In other words, optical rotation, like melting or  boiling points, is a physical property of a compound, whereas \("R, S, D\) and \(L" \) are conventions humans use to depict the structure of the molecule.