Organic Chemistry

Summary of Reactions 955

projection; the is equatorial when a sugar is
shown in a chair conformation and up when the sugar is
shown in a Haworth projection. At equilibrium, there is more

• D-glucose than -D-glucose. -D-Glucose and -D-glucose
  are anomers—they differ in configuration only at the carbon
  (anomeric carbon) that was the carbonyl carbon in the open-
  chain form. Anomers have different physical properties. Six-
  membered-ring sugars are pyranoses; five-membered-ring
  sugars are furanoses. The most abundant monosaccharide in
  nature is D-glucose. All the OH groups in -D-glucose are in
  equatorial positions. A slow change in optical rotation to an
  equilibrium value is known as mutarotation.
  The cyclic hemiacetal (or hemiketal) can react with an
  alcohol to form an acetal (or ketal), called a glycoside. If
  the name “pyranose”or “furanose”is used, the acetal is
  called a pyranosideor a furanoside. The bond between the
  anomeric carbon and the alkoxy oxygen is called a
  glycosidic bond. The preference for the axial position by
  certain substituents bonded to the anomeric carbon is called
  the anomeric effect. If a sugar has an aldehyde, ketone,
  hemiacetal, or hemiketal group, it is a reducing sugar.
  Disaccharidesconsist of two monosaccharide subunits
  hooked together by an acetal linkage. Maltose has an

b

b a a b

b-position cellobiose has a

The most common disaccharide is sucrose; it

consists of a D-glucose subunit and a D-fructose subunit

linked by their anomeric carbons.

Polysaccharidescontain as few as 10 or as many as

several thousand monosaccharide units joined together by

glycosidic linkages. Starch is composed of amylose and

amylopectin. Amylose has unbranched chains of D-glucose

units joined by linkages. Amylopectin, too,

has chains of D-glucose units joined by

linkages, but it also has linkages that create

branches. Glycogen is similar to amylopectin, but has more

branches. Cellulose has unbranched chains of D-glucose units

joined by linkages. The cause

amylose to form a helix; the allow the molecules

of cellulose to form intramolecular hydrogen bonds.

The surfaces of many cells contain short polysaccharide

chains that allow the cells to interact with each other. These

polysaccharides are linked to the cell surface by protein

groups. Proteins bonded to polysaccharides are called

glycoproteins.

b-linkages

b-1,4¿-glycosidic a-linkages

a-1,6¿-glycosidic

a-1,4¿-glycosidic

a-1,4¿-glycosidic

sidic linkage.

A-1,4œ-glycosidic linkage; B-1,4œ-glyco-

Summary of Reactions

1. Reduction (Section 22.5).


2. Oxidation (Section 22.5).

a. c.

b. d. HNO^3

(CHOH)n ∆

CH 2 OH

HC O

(CHOH)n

COOH

COOH

Ag+, NH 3

(CHOH)n HO− + Ag

CH 2 OH

CO

(CHOH)n

CH 2 OH

CH 2 OH COO−

CHOH

+ 2 Br−

Br 2

(CHOH)n H 2 O

CH 2 OH

HC O

(CHOH)n

CH 2 OH

COOH

Ag+, NH 3

(CHOH)n HO−

CH 2 OH

HC O

(CHOH)n + Ag

CH 2 OH

COO−

H 2

(CHOH)n Pd/C

CH 2 OH

HC O

(CHOH)n

CH 2 OH

CH 2 OH

1. NaBH 4
   2. H 3 O+

(CHOH)n

CH 2 OH

CO

(CHOH)n

CH 2 OH

CH 2 OH CH 2 OH

CHOH