chapter 7 section 2

Question 1

What determines if a monosaccharide is an aldose or a ketose?

Answer 1

Aldoses have an aldehyde group; ketoses have a ketone group.

Question 2

What are the simplest aldose and ketose?

Answer 2

Glyceraldehyde (aldose) and dihydroxyacetone (ketose)

Question 3

What are trioses?

Answer 3

Monosaccharides with three carbon atoms

Question 4

What are hexoses?

Answer 4

Six-carbon sugars; the most abundant in nature.

Question 4

How is the D,L system of nomenclature determined?

Answer 4

By the configuration of D- or L-glyceraldehyde.

Question 4

How do you name monosaccharides based on carbons and functional groups?

Answer 4

Use terms like aldotetroses, ketopentoses, aldohexoses, etc

Question 4

What is an alternative naming method for ketoses?

Answer 4

nsert “-ul-“ into the generic term (e.g., pentulose, hexulose).

Question 4

What are common characteristics of the simplest monosaccharides?

Answer 4

Water soluble and mostly sweet.

Question 4

Which monosaccharides contain chiral centers?

Answer 4

Aldoses with ≥3 carbons and ketoses with ≥4 carbons

Question 4

What projection system is commonly used to depict monosaccharide stereochemistry?

Answer 4

Fischer projection.

Question 4

In Fischer projections, what determines D or L configuration?

Answer 4

The position of the hydroxyl group on the highest numbered asymmetric carbon.

Question 4

Does D or L indicate the direction of optical rotation?

Answer 4

No; D/L only relates configuration to glyceraldehyde.

Question 4

How can optical rotation be indicated?

Answer 4

By adding a + (dextrorotatory) or – (levorotatory) sign, e.g., D(+)-glucose or D(–)-fructose.

Question 4

Which form predominates in nature: D- or L-monosaccharides?

Answer 4

D-forms; L-forms are rare and specialized.

Question 5

What are enantiomers?

Answer 5

Nonsuperimposable mirror-image stereoisomers

Question 5

What are diastereomers?

Answer 5

Stereoisomers with opposite configurations at one or more chiral centers but not mirror images.

Question 5

What are epimers?

Answer 5

Sugars differing in configuration at only one chiral center

Question 5

Give an example of epimers

Answer 5

D-glucose and D-mannose

Question 5

What structural feature do Fischer projections fail to show in monosaccharides?

Answer 5

The ability to form cyclic structures

Question 5

What is a hemiacetal?

Answer 5

A compound formed when an alcohol reacts with an aldehyde.

Question 5

How do aldoses like glucose form cyclic structures?

Answer 5

The aldehyde reacts intramolecularly with a hydroxyl to form a cyclic hemiacetal.

Question 5

What is a pyranose?

Answer 5

A six-membered cyclic sugar ring, similar to pyran

Question 5

How is cyclization of glucose catalyzed?

Answer 5

By acid (H⁺) or base (OH⁻); the reaction is reversible.

Question 5

How do ketoses like fructose form cyclic structures?

Answer 5

The ketone reacts intramolecularly with a hydroxyl to form a hemiketal.

Question 5

What is a furanose?

Answer 5

A five-membered cyclic sugar ring, similar to furan.

Question 5

Which form of monosaccharides predominates in aqueous solution?

Answer 5

Cyclic pyranose and furanose forms; the linear form is <1%

Question 5

What is the anomeric carbon?

Answer 5

The carbon that was the carbonyl in the linear sugar, becomes asymmetric in the cyclic form.

Question 5

What are α and β anomers?

Answer 5

α: hydroxyl at anomeric carbon on same side as the highest numbered asymmetric carbon; β: opposite side.

Question 5

What property allows α and β forms to be distinguished?

Answer 5

Optical rotation of plane-polarized light.

Question 5

What is mutarotation?

Answer 5

The interconversion of α- and β-anomers through the linear form, changing optical rotation over time.

Question 5

What are the specific rotations of α-D-glucose and β-D-glucose

Answer 5

α-D-glucose: +112.2°; β-D-glucose: +18.7°.

Question 5

What is a Haworth projection?

Answer 5

A way to draw cyclic sugars as planar pentagons or hexagons, showing substituents above or below the ring

Question 5

How are substituents from Fischer projections positioned in Haworth projections?

Answer 5

Left → above the ring, Right → below the ring (for D-sugars)

Question 5

How are α- and β-anomers represented in Haworth projections for D-sugars?

Answer 5

α: anomeric OH below the ring; β: anomeric OH above the ring.

Question 5

What determines whether a monosaccharide forms a furanose or pyranose ring?

Answer 5

Which hydroxyl reacts with the carbonyl; structural factors; ring strain.

Question 5

Why don’t six-carbon sugars form seven-membered rings?

Answer 5

Seven-membered rings are too strained and unstable

Question 5

Which ring size is generally favored for aldohexoses?

Answer 5

Six-membered pyranose rings.

Question 5

Which ring size tends to be more stable for ketohexoses?

Answer 5

Five-membered furanose rings.

Question 5

Do Haworth projections show true ring conformations?

Answer 5

No; real rings are puckered due to tetrahedral bond angles.

Question 5

What are the two main pyranose conformations?

Answer 5

Chair and boat conformations.

Question 5

What is the difference between equatorial and axial substituents?

Answer 5

Equatorial ≈ coplanar with the ring; axial ≈ parallel to the ring axis.

Question 5

Which conformation is more stable for pyranose rings?

Answer 5

Chair conformation; bulky groups prefer equatorial positions.

Question 5

Why is β-D-glucose so common in nature?

Answer 5

t can adopt a chair conformation with all bulky groups equatorial, giving high stability.

Question 5

How are acetals and ketals formed from sugars?

Answer 5

Hemiacetals/hemiketals react with alcohols under acid to form acetals or ketals (dehydration synthesis).

Question 5

What is a glycosidic bond?

Answer 5

The bond between the anomeric carbon of a sugar and the oxygen of an alcohol in a glycoside.

Question 5

How are glycosides named?

Answer 5

Based on the parent monosaccharide, e.g., methyl-β-D-glucoside.

Question 5

What are muramic acid and neuraminic acid?

Answer 5

Amino sugar derivatives linked to three-carbon acids in bacterial and animal cell walls.

Question 5

What are sialic acids?

Answer 5

N-acetyl and N-glycolyl derivatives of neuraminic acid found in bacteria and animals

Question 5

What defines amino sugars?

Answer 5

Monosaccharides with an amino group replacing a hydroxyl, often at C-2

Question 5

Where are amino sugars commonly found?

Answer 5

In oligosaccharides, polysaccharides, and chitin (exoskeletons of crustaceans/insects)

Question 5

What are sugar esters?

Answer 5

Sugars with phosphate groups; important in metabolism

Question 5

What are deoxy sugars?

Answer 5

Monosaccharides with one or more hydroxyl groups replaced by hydrogen

Question 5

Name two common 6-deoxy sugars.

Answer 5

L-Fucose and L-Rhamnose.

Question 5

What is the role of rhamnose in ouabain?

Answer 5

It is part of the sugar moiety; the sugar itself is not toxic

Question 6

How are sugar alcohols (alditols) formed

Answer 6

By mild reduction of the carbonyl groups of aldoses/ketoses

Question 7

Can sugar alcohols cyclize?

Answer 7

No, they are linear molecules.

Question 8

Name three common sugar alcohols used as sweeteners

Answer 8

Sorbitol, mannitol, xylitol.

Question 9

What is a potential health concern of sorbitol?

Answer 9

Buildup in diabetic eyes may contribute to cataract formation.

Question 10

Name two biologically important sugar alcohols.

Answer 10

Glycerol (lipids) and myo-inositol

Question 11

What is ribitol a constituent of?

Answer 11

Flavin coenzymes.

Question 12

What happens when sugars with free anomeric carbons react with oxidizing agents?

Answer 12

They are converted to sugar acids.

Question 13

Give an example of a chemical test for reducing sugars

Answer 13

Fehling’s test: aldose reduces Cu²⁺ to red Cu₂O precipitate, forming an aldonic acid.

Question 14

What are reducing sugars?

Answer 14

Sugars that can reduce oxidizing agents due to a free anomeric carbon.

Question 15

How is the concentration of reducing sugars determined?

Answer 15

By measuring how much oxidizing agent they reduce.

Question 16

Why is testing for reducing sugars clinically important?

Answer 16

High glucose in blood or urine is a marker for diabetes mellitus.

Question 17

What are uronic acids?

Answer 17

Sugars oxidized enzymatically at C-6

Question 18

How does L-iduronic acid differ from D-glucuronic acid?

Answer 18

Opposite configuration at C-5.

Question 19

What are aldaric acids?

Answer 19

Sugars oxidized at both C-1 and C-6