Second Half I F24: Lecture Slides 34 - 57

Question 1

What are sugars considered to be?

Answer 1

The most abundant biomolecule on earth.

Question 2

What are sugars important in?

Answer 2

Energy Metabolism

Question 3

What are sugars essential components of?

Answer 3

Nucleic Acids

Question 4

What are Monosaccharides?

Answer 4

Consist of a single sugar unit (Glucose)

Question 5

What are Oligosaccharides?

Answer 5

Short chains of Monosaccharide Units (Sucrose)

Question 6

What are Polysaccharides?

Answer 6

Polymers of 20 or more sugar units (Glycogen, cellulose)

Question 7

What are the 4 chemical properties of Monosaccharides?

Answer 7

• Very water soluble
• Poorly soluble or insoluble in organic solvents such as ether or hexane.
• Colourless
• Sweet to Taste

Question 8

What is the approx. chemical formula of Monosaccharides?

Answer 8

(CH2O)n

Question 9

What are the two organic functional groups that combine to make a monosaccharide?

Answer 9

A carbonyl (C = O) group , which can either be an aldehyde or ketone and at least two carbons bearing hydroxyl (alcohol) C - OH groups

Question 10

What do the simplest carbon atoms contain?

Answer 10

Three carbon atoms (Trioses)

Question 11

What do each of the trioses have?

Answer 11

They have aldoses and ketoses: aldotriose and ketotriose

Question 12

What is glycerol considered to be?

Answer 12

An aldose

Question 13

What is acetone considered to be?

Answer 13

A ketoses

Question 14

What did Emil Fischer study?

Answer 14

He studied the analysis, synthesis and stereochemistry of simple sugars, and he introduced much of the terminology and notation that we use today

Question 15

What is the Fischer projection formula?

Answer 15

To represent three dimensional sugar structures on paper

Question 16

In the Fisher projection formula, how are vertical bonds represented?

Answer 16

Behind the plane

Question 17

In the Fisher projection formula, how are horizontal bonds represented?

Answer 17

Project out of the planar

Question 18

What is the Perspective Formula?

Answer 18

Solid Wedge-Shaped Bonds Project in front

Dashed bonds point away

Question 19

What are the carbon atoms in Monosaccharides?

Answer 19

Asymmetric (4 different substituents)

Question 20

What do all monosaccharides except dihydroxyacetone contain?

Answer 20

One or more chiral carbon atoms

Question 21

What does chiral carbon atoms give rise to?

Answer 21

The occurrence of optically active isomeric forms (a type of stereoisomer)

Question 22

What are D Glyceraldehyde and L Glyceraldehyde?

Answer 22

Enantiomers (mirror images)

Question 23

What are mirror images?

Answer 23

Differ in Configuration at every chiral carbon atom (can’t be superimposed)

Question 24

What are the chemical properties of Mirror images

Answer 24

Identical (melting point, water-solubility)

Question 25

What do mirror images differ in?

Answer 25

Optical activity

Question 26

What is Optical Activity?

Answer 26

The plane of polarization of polarized light is bent in opposite directions when passing through solutions of the two enantiomers

Question 27

What are Diastereomers?

Answer 27

More then one chiral carbon atoms that have stereoisomers that differ in hardness at some carbon atoms but not others (not mirror images)

Question 28

Do diastereomers have identical chemical properties?

Answer 28

They do not have identical chemical properties, because the spatial relationships among the atoms making up the molecules are different

Question 29

When would a sugar be called a "D" sugar?

Answer 29

If the chiral carbon atom furthest away from the carbonyl group has the same configuration as D-glyceraldehyde.

Question 30

What are "L" sugars?

Answer 30

Those with a configuration similar to L-glyceraldehyde

Question 31

What configuration are most naturally occurring sugars in?

Answer 31

D-sugars

Question 32

What are Epimers?

Answer 32

A pair of sugars that are identical expect for one configuration at one carbon atom (at the chiral centre they have one identical structure at one carbon)

Question 33

What are epimers a special case of?

Answer 33

Diastereomers

Question 34

What is the formula for figuring out the number of stereoisomers?

Answer 34

2^n (the power is the # of chiral centres)

Question 35

What is an example of the number of stereoisomers for n chiral centres of aldose?

Answer 35

An aldose have 5 carbons with 3 chiral centres 2^3 = 8 stereoisomers.

Question 36

What happens to D-ketoses every time a C atom is added?

Answer 36

The number of isomers doubles

Question 37

What is the general trend with D-Aldoses?

Answer 37

A aldose has one more chiral centre than a ketone, so the number doubles.

Question 38

What do Aldehydes and Ketones produce when they react with alcohols?

Answer 38

Hemiacetals and Hemiketals

Question 39

What happens to the original carbonyl carbon upon the formation of hemiacetals and hemiketals?

Answer 39

It becomes chiral

Question 40

What is the hemiacetal and hemiketal formation?

Answer 40

Intramolecular: the alcohol and the aldehyde (or ketone) are present in the same molecule

Question 41

What does hemiacetal and hemiketal formation turn sugars into?

Answer 41

Ring structures

Question 42

What does the OH group at C-5 react with?

Answer 42

The carbonyl carbon of the aldehyde group to form a stable six-membered ring.

Question 43

What does the OH group reaction render?

Answer 43

A C-1 asymmetric giving rise to two stereoisomers (a and b)

Question 44

What do these isomeric forms differ in?

Answer 44

Only in their configuration around the hemiacetal or hemiketal carbon

Question 45

What is the difference in the configuration around the hemiacetal or hemiketal carbon called?

Answer 45

An anomer

Question 46

What does the electrophilic carbonyl carbon atom react with?

Answer 46

The nucleophilic O of an OH group

Question 47

What is solid glucose found in?

Answer 47

Either in the alpha or the beta form of the hemiacetal

Question 48

What happens as it dissolves in water?

Answer 48

It slowly converts into an equilibrium mixture of the alpha, beta and linear forma.

Question 49

What is the process of it converting into the equilibrium mixture called?

Answer 49

Mutarotation

Question 50

What happens with time?

Answer 50

A solution of a-D-glucose and b-D-glucose form identical equilibrium mixtures with identical optical properties

Question 51

What is the approximate composition?

Answer 51

1/3 a-D-Glucose, 2/3 B-D-Glucose, and trace amounts of linear form.

Question 52

What are the two rings formed when sugars cyclize?

Answer 52

Pyranose (6-membered) or Furanose (5 membered)

Question 53

What does the size of the ring formed by a particular sugar depend on?

Answer 53

The relative thermodynamic stabilities of the various possible ring structures, and this depends on the particular geometry of the molecule.