Unformatted text preview: e two iso mers of the carbohydrate erythrose can be drawn as shown below. Note that each mo lecule has two chiral carbons. Lerythrose Derythrose · By convent ion, Fisher project ions are written with the most highly oxidized carbon (carbonyl) written on top. The L iso mer is assigned to the lefthanded stereoiso mer (with ¾OH on the left side o f the chiral carbon), and D iso mer is assigned to the righthanded stereoiso mer (with ¾OH on the right side of the chiral carbon). Examples: Determine if each Fisher project ion shown below is a chiral co mpound. If so, ident ify it as the D or L iso mer, and draw the mirror image. 1) 2) 3) 6 Chemistry 52 Chapter 26 ENANTIOMERS
· Chiral mo lecules that are nonsuperimposable mirror images of each other are stereoiso mers and are called enantiomers. Enant iomers are related to one another as a right hand is related to a left hand. Enantiomers of lactic acid · Enantio mers possess similar chemical and physical properties (except for rotation of light). They rotate planepolarized light to the same degree but in different direction.
· Enantio mers possess different biochemical properties. For example: Ø (+)Glucose (“blood sugar”) is used for metabo lic energy whereas ()glucose is not. Ø (+)Lactic acid is produced by reactions occurring in muscle tissue, and ()lact ic acid is produced by the lact ic acid bacteria in the souring of milk.
· In compounds with only one chiral carbon, the relationship between enant io mers is such that if we change the posit ion of any two groups attached to a chiral carbon, we obtain the structure of its enantio mer (Isomers I and II).
· If we make a second change, the structure of the original iso mer is obtained (Isomers I and III). CH3 COOH COOH cha
H OH ¬¾ng e posCOO Hf ® H OH ¬¾nge position of ® HO H ¾ ¾ion o¾
CH and H and OH
3 COOH Isomer I CH3 CH3 Isomer II Isomer III 7 Chemistry 52 Chapter 26 ENANTIOMERS
· When evaluat ing different Fisher pro...
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