Chemistry 106 Lecture Notes Examination 5 Materials. *Hydrated Carbons.

Transcription

1 hemistry 106 Lecture Notes Examination 5 Materials hapter 23: arbohydrates & Nucleic Acids arbohydrates Definition: *ompounds made of,, &. Example: *ydrated arbons. Glucose: an be written as 6( 2 ) or 6 [6( 2 )] lassifications: a) Monosaccharides: Simple arbohydrates that are not cleaved upon an attempt of hydrolysis, into simpler carbohydrates. Example: Glucose, Fructose b) Disaccharides: Are cleaved (hydrolyzed) into two monosaccharide units. Example: Sucrose c) ligosaccharides: Are made of 3-10 monosaccharide units. ommonly found on the plasma membrane of animal cells d) Polysaccharides: Are made of more than10 monosaccharide units. Example: ellulose, starch. 1

2 Monosaccharides: Methods of classifying Monosaccharides: 1. Based on the functional group on 1 o r 2 of the sugar: a) Aldoses: Possess aldehyde group on 1. b) Ketoses: Possess ketone group on 2. Example: 2 2 Glucose An Aldose Fructose A Ketose 2. Based on the total number of carbons in the sugar unit: a) Triose: 3 carbons (total) in the sugar molecule. b) Tetrose: 4 carbons (total) in the sugar molecule. c) Pentose: 5 carbons (total) in the sugar molecule. d) exose: 6 carbons (total) in the sugar molecule. e) eptose: 7 carbons (total) in the sugar molecule. f) ctose: 8 carbons (total) in the sugar molecule. Example:

3 The two classification methods (1 & 2 above) could be used in a combined fashion: Based on D (+) and L ( ) glyceraldehydes: (D and L notation): D-(+) Glyceraldehyde L-( ) Glyceraldehyde appens to be R appens to be S pointing to RIGT in Fischer pointing to LEFT in Fischer This system of naming/classification is extrapolated to larger monosaccharides: If the hydroxyl group on the ighest Numbered hiral arbon points to RIGT when drawn in Fischer projection (with the aldehyde or ketone carbon upward): D Sugar therwise, it is an L-Sugar 3

4 Examples: D L D L 2 2 L D yclic Forms of Sugars: Sugars also exist in cyclic form, as well as open-chain form. Types: 1. Furanose: 5 membered ring. 2. Pyranose: 6 membered ring. 2 4

5 The cyclic & the open-chain conformers are interconverted: Example: 2 D-glucose D-glucopyranose 2 D-Glucose D-glucofuranose 5

6 ow to Draw the yclic Form: 90 o becomes protonated 6 2 becomes a member of the ring Anomeric arbon 2 Points up in cyclic D-sugars

7 onformation around the 1: Trans is α form β form α and β forms are called Anomers of each other Which anomer is more stable?why? Mutarotation: The process during which anomers are interconverted (going through the open chain): 7

8 Mechanism: 8

9 Deoxy Sugars: Sugars with one or more of the hydroxyl groups replaced by hydrogens: Amino Sugars: Sugars with one or more of the hydroxyl groups replaced by amino groups: N 2 Glycosides: Sugars with the anomeric hydroxyl group replaced by other groups: N Laboratory Preparation of Glycosides: Sugar + Alcohol Anomeric mixture of glycosides + 3 l (Major) 9 3

10 Mechanism:

11 Disaccharides: Structurally, disaccharides are glycosides. ellobiose: Glucose + Glucose Glycosidic Linkage Maltose: Glucose + Glucose 11

12 2 Sucrose 2 l 2 l Sucralose 2 l 12

13 Polysaccharides: ellulose: 13

14 Reactions: 1. Reduction of arbohydrates: a) With NaB 4, 2 : yclic Forms NaB 4, 2 Also using 2, Ni hydrogenation. 2 2 "Alditol" 2. xidation of arbohydrates: a) Using Benedict s Reagent: Targets & oxidizes the terminal aldehyde group. The product is generally called an aldonic acid. yclic Forms Benedict's Reagent 2 2 "Aldonic Acid" Benedict s Reagent: [us 4, citric acid complex], basic condition. R + us R + u Also Fehling s reagent: [us 4, tartaric acid complex], basic condition Also Br 2, 2. 14

15 b) Using N 3 : Targets & oxidizes the terminal aldehyde and the 1 o alcohol groups into carboxylic acids. The product is generally called an aldaric acid. yclic Forms N 3, 60 o "Aldaric Acid" 2 extended. 2. yanohydrin Formation & hain Extension (AKA: Kiliani-Fischer Synthesis): The reaction is specific to aldoses. yanohydrin is formed and the chain is N N N **To convert the N group into aldehyde group: N 2, 2 Pd/BaS

16 4. Isomerization (Epimerization):, 2, 2 Mechanism: 2 2 Enediol Intermediate 2 16

17 5. Acylation & Alkylation of ydroxyl Groups: + 5 N Ac Ac Ac Ac Ac I Ag Follow up Reaction:

18 6. Periodic xidation: This reaction cleaves the sugars into oxidized fragments (alcohols into aldehydes/ketones, or into carboxylic acids, and aldehydes into carboxylic acids). Periodic acid!-d-glucose 3 methyl-d-glucopyranoside 2I