CH 15 - CHEM 120

stereochemistry

the study of the three-dimensional structure of molecules

stereoisomers

have the same connectivity but a different orientation of their atoms in space

enantiomers

nonsuperimposable mirror images; have same physical properties except interaction w/ plane polarized light

chiral carbon

carbon atom attached to four different atoms or groups of atoms

distereomers

stereoisomers that are not mirror images of each other; different physical and chemical properties

meso compounds

superimposable mirror images even though they contain chiral centers (internal plane of symmetry)

what are optically active compounds?

those that contain one or more chiral centers but are NOT meso compounds

why can't meso compounds be optically active compounds?

the rotations of their chiral centers cancel each other out

carbohydrate

simple or complex sugar composed of carbon, hydrogen, and oxygen

what is the most important simple carbohydrate?

glucose

formula for glucose

C₆H₁₂O₆ or C₆(H₂O)₆

monosaccharides

single sugar units

ogliosaccharides

contain several monosaccharides bound together (2 - 10)

disaccharides

two sugar units

polysaccharides

more than 10 sugar units

what is the suffix for sugar molecules?

-ose

what are 5 important monosaccharides?

D-glyceraldehyde

D-glucose

D-fructose

D-galactose

D-ribose

simplest sugar w/ only one chiral center

D-glyceraldehyde

aldohexose; common names include dextrose, grape sugar, blood sugar

D-glucose

ketohexose; sweetest of all natural sugars

D-fructose

common part of lactose; converts ingested galactose to glucose

D-galactose

used in genetic material; not used as an energy source, but is a part of the backbone of RNA

D-ribose

what is the most abundant organic compound found in nature?

D-glucose

what does a sugar become when the C-2 OH is removed from D-ribose?

deoxyribose (used in DNA)

Which group of carbohydrates cannot be hydrolyzed to give smaller molecules?

monosaccharides

A ketose is a ______ with ______ functional group.

monosaccharide; a ketone

An aldose is a ______ with ______ functional group.

monosaccharide; an aldehyde

cellulose

an unbranched chain of D-glucose units connected by β-1,4-glycosidic bonds

amylose

an unbranched chain of D-glucose units connected by α-1,4-glycosidic bonds

L isomer

-OH group is on the left of last chiral carbon

D isomer

-OH group is on the right of last chiral carbon

furanoses

five-membered cyclic forms of sugars

pyranoses

six-membered cyclic forms of sugars

anomers

the -OH that forms from the ring closure can either be above or below the plane of the ring

α-anomer

the hydroxyl group on the anomeric carbon is in the opposite direction as the CH₂OH group (below)

β-anomer

the hydroxyl group on the anomeric carbon is in the same direction as the CH₂OH group (above)

mutarotation

the equilibrium between α and β forms, allowing conversion from one form to another

how are disaccharides connected?

by glycosidic bonds between the anomeric carbon of one unit & an -OH of another unit

sucrose is a disaccharide formed by linking what?

α-D-glucose with β-D-fructose

maltose is a disaccharide formed by linking what?

two α-D-Glucose units

lactose is a disaccharide formed by linking what?

β-D-Galactose and α-D-Glucose