Chem120 Chp 15 Carbohydrates

carbohydrates

aka “saccharides” (sugar, in greek)

major energy source in food

molecular formula of (C(H₂O))_n

glucose: C₆H₁₂O₆

carbohydrates: glucose

produced by photosynthesis in plants

synthesized in plants from CO₂, H₂O and energy from the sun

oxidized in living cells to produce CO₂, H₂O and energy

types of carbohydrates

monosaccharides — one repeating sugar subunit

disaccharides — two repeating sugar subunits

polysaccharides — many repeating sugar subunits

monosaccharides

3-6 carbon atoms (typically)

a carbonyl group (aldehyde or ketone)

hydroxyl groups on all carbons, except the carbonyl group

polyhydroxyaldehyde, polyhydroxyketone

classification of monosaccharides

-ose

triose (3 C atoms)

tetrose (4 C atoms)

pentose (5 C atoms)

hexose (6 C atoms)

aldoses

monosaccharides with an aldehyde group

• aldotriose (3 C atoms)

• aldotetrose (4 C atoms)

• aldopentose (5 C atoms)

• aldohexose (6 C atoms)

ketose

monosaccharides with a ketone group (C2 position)

• ketotriose (3 C atoms)

• ketotetrose (4 C atoms)

• ketopentose (5 C atoms)

• ketohexose (6 C atoms)

achiral

object whose mirror image is identical to the original and can be superimposed on (e.g. baseball bat)

chiral

objects that have non-superimposable mirror images (e.g. gloves)

chiral compounds

carbon atoms are chiral if they are bonded to four different atoms or groups

stereoisomers

same molecular formula

chiral carbon

differ in 3D arrangement of their atoms in space

enantiomers pt1

mirror images of chiral carbon compounds

stereoisomers that cannot be superimposed

non-superimposable mirror images r called enantiomers

enantiomers pt2

same physical properties, except the direction they rotate polarized light

identified by D- and L-

natural sugars are D- forms

Fisher projection

2D representation of a chiral molecule

places the most oxidized group at the top (aldehyde)

use vertical lines for bonds that go back

use horizontal lines for bonds that go forward

chiral carbons at the intersection

D- and L- Enantiomers

determined by the -OH farthest away from the most oxidized group

• L- isomer has -OH to the left of the chiral carbon

• D- isomer has the -OH to the right of the chiral carbon

monosaccharides to memorize

D-glucose, D-galactose, D-fructose

• all hexoses

• all have molecular formula of C₆H₁₂O₆

• all isomers of each other

D-glucose (dextrose)

C₆H₁₂O₆

most common hexose

found in fruits, veggies, honey

aka dextrose or blood sugar in body

monosaccharide in polymers of starch, cellulose, and glycogen

D-galacatose

aldohexose with C₆H₁₂O₆

not found free in nature

obtained from lactose (disaccharide) (glacatose + glucose)

important in the cellular membranes of the brain and nervous system

D-fructose

a ketohexose with C₆H₁₂O₆

sweetest carbohydrate

found in fruit juices and honey

converted to glucose in the body

Haworth structures

right structure of saccharides

produced after the reaction of a carbonyl group and a hydroxyl group in the same molecule (hemiacetal reaction)