The d and l Notation

The second carbon of lactic acid is chiral with four different groups attached H, OH, CH3, and COOH. The chiral carbon is placed at the intersection of two lines. Lactic acid is not an aldehyde, but it does contain a carbon-oxygen double bond (in the carboxyl group). This carboxyl group is placed at the top of the vertical line. The direction of the —OH groups on the chiral carbons determines the d and l notations ... 

The ct-carbon of all the naturally occurring amino acids (except glycine) is an asymmetric center. Therefore, 19 of the 20 amino acids listed in Table 22.2 can exist as enantiomers. The D and l notation used for monosaccharides (Section 21.2) is also used for amino acids. 

Note that the d and l notations have no relation to the direction in which a given sugar rotates plane-polarized light. A d sugar can be either dextrorotatory... 

Italic/or p sufixes indicate a ring size respectively /for furanose (five membered rign), and p for pyranose (six-membered ring). The D and l notation refer to the relative configuration of sugars. 

The Cahn-Ingold-Prelog system is the standard method of stereochemical notation. It replaced an older system based on analogies to specified reference compounds that used the prefixes d and l, a system that is still used for carbohydrates and amino acids. We will use d and l notation when we get to Chapters 23-26, but won t need it until then. 

Chapter 13, Carbohydrates, describes the carbohydrate molecules monosaccharides, disaccharides, and polysaccharides and their formation by photosynthesis. Monosaccharides are classified as aldo or keto pentoses or hexoses. Chiral molecules, moved from Chapter 12 to Chapter 13, are discussed along with Eischer projections and d and l notations. An Explore Your World feature models chiral objects using gumdrops and toothpicks. Carbohydrates used as sweeteners are described and carbohydrates used in blood typing are discussed. The formation of glycosidic bonds in disaccharides and polysaccharides is described. 

The a-carbon of all amino acids, with the exception of glycine, has four different substituent groups and is therefore an asymmetric carbon atom. Such an atom can exist in two different spatial arrangements which are mirror images of each other. These structural forms of molecules are known as stereoisomers and the common notation of D and L forms is used, a nomenclature that refers to their absolute spatial configuration when compared with that of glyceraldehyde (Figure 10.4). 

Show a Fischer projection for each of the four possible stereoisomers of 2-methylbutane-l,2,3,4-tetraol. Label each chiral center as jR or S and label each structure with the d or l and the erythro or threo notation. 

Monosaccharides contain at least one asymmetric C atom and are therefore capable of existing in D and L optically active forms (Chapter 13.2). In Table 10.2, the complete scheme of D-monosaccharides is shown, in shortened notation, for up to 6 C atoms. 

Fig. 4.14 (a) Two-photon induced photoluminescence from a single gold nanorod. (b) Symmetry points and axes in the first Brilloiun zone of gold, (c) Band structures of gold near the X and L symmetric points. The notations sp and d denote, respectively, the sp conduction band and the d valence band. The dashed line Fermi energy level. h(Opi photon energy of photoluminescence radiated through recombination of an electron-hole pair... 

Instead of using directly a sequence of quantum numbers to characterize an electronic level, the overall quantum numbers are usually expressed using a specific notation called spectroscopic terms, spectroscopic levels, and spectroscopic sublevels. A spectroscopic term P5+i)p is determined by the S and L overall quantum numbers. It defines the multiplicity of the overall spin angular momentum and represents the overall orbital quantum number as a capital letter F = S, P, D, F, G, H, etc. that corresponds to values of L =0, 1,2,3,4, 5, etc. 

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