1 (745)

Prévia do material em texto

24 Organic and Biological Chemistry Solutions to Exercises CH₂OH H H H H H o H o H H H H H OH H OH H OH H OH H HO OH HO H OH H OH H OH H OH H OH α-linkage 24.69 The empirical formula of cellulose is C₆H₁₀O₅. As in glycogen, the six-membered ring form of glucose forms the monomer unit that is the basis of the polymer cellulose. In cellulose, glucose monomer units are joined by linkages. 24.70 The empirical formula of glycogen is C₆H₁₀O₅. The six-membered ring form of glucose is the unit that forms the basis of glycogen. The monomeric glucose units are joined by α linkages. 24.71 (a) In the linear form of mannose, the aldehydic carbon is C1. Carbon atoms 2, 3, 4, and 5 are chiral because they each carry four different groups. Carbon 6 is not chiral because it contains two H atoms. (b) Both the α (left) and (right) forms are possible. 6 5 H H H OH H 4 H OH OH OH 1 OH OH C OH OH 3 H H H H H 24.72 (a) In the linear form of galactose, the aldehydic carbon is C1. Carbon atoms 2, 3, 4, and 5 are chiral because they each carry four different groups. Carbon 6 is not chiral because it contains two H atoms. (b) The structure is best deduced by comparing galactose with glucose, and inverting the configurations at the appropriate carbon atoms. 5 OH Recall from Solution 25.68 that both the ß-form 4 C H C1 OH H (shown here) and the α-form (OH on carbon 1 on the opposite side of ring as the CH₂ OH on carbon 2 H H OH 5) are possible. galactose 24.73 The term lipid refers to the broad class of naturally-occurring molecules that are soluble in nonpolar solvents. Two important subgroups are fats and fatty acids. Structurally, fatty acids are carboxylic acids with a hydrocarbon chain of more than four carbon atoms (typically 16-20 carbon atoms). Fats are esters formed by condensation of an alcohol and a fatty acid. In animals, the alcohol is the triol glycerol; three fatty acid molecules condense with one glycerol molecule to form a large, nonpolar molecule. For both fatty acids and fats it is the long hydrocarbon chains that define the polarity, solubility and other physical properties of the molecules. 739