Carbohydrates

Question 1

Examples of monosaccharides

Answer 1

• Glucose (6 membered ring)
• Mannose (6 membered ring)
• Galactose (6 membered ring)
• Fructose (5 membered ring)
• Ribose (5 membered ring)

Question 2

Functional groups

Answer 2

• Alcohol - can be nucleophiles and attack nucleophilic centres, polar, hydrogen bonding, watersolubility
• Ether - non-reactive on its own but this isnt on its own
• Hemiacetal

Question 3

Cyclisation

Answer 3

• Where the sugar ring opens up to fold in different ways
• Opens up by the electrons on oxygen forming a new bond with the carbon
• 5 membered rings are called furanose
• 6 membered rings are called pyranose
• Pyranose forms typically dominate

Question 4

Anomers - open chain

Answer 4

• If you have the open chain form and want to make the 6 membered ring again, it can attack from above or below
• If you attack from above it will form an axial OH bond (alpha)
• If you attack from below it forms a equatorial OH bond (beta)
• The aldehyde carbon in the open chain form is known as the anomeric position

Question 5

Nomenclature

Answer 5

• Either alpha (axial anomeric position) or beta (equatorial anomeric position) at the start
• Then D or L stereochemistry (usually D in nature)
• Then the descriptive name (number of carbons)
• then pyranose or furanose for if its 6 or 5 membered ring

Question 6

Anomeric effect

Answer 6

• Axial alpha arrangement (up or down) is less stable than the equatorial beta arrangement because they have less repulsion and more space compared to the axial arrangement - with normal 6 ring, with 6 substiuents
• With 1 substiuent or with an oxygen in the ring it will pefer to be equatorial than axial
• If you have two oxygens in the ring (OH and an O) it will prefer to be axial than equitorial because of hyperconjugation, dipole aligment (less repulsion as dipoles are perpendicular) and the proximity of lone pairs

Question 7

Aldo/keto and hexose/pentose

Answer 7

• Sugars may have an aldehyde or ketone in open chain form
• Aldehydes are easy to oxidise = reducing sugars
• If when the sugars open up they make an aldehyde they are called a aldose, if they make a ketone theyre called a ketose

Question 8

Oligosaccharides

Answer 8

When multiple sugars are bonded together

Question 9

Polysaccarides

Definition and examples

Answer 9

Saccharides joined together into polymers
* Amylose
* Cellulose
* Chitin

Question 10

Glycosides

Answer 10

• Saccharides attached to other molecules
• Small non-sugar molecule attached through anomeric position to a sugar