Simple carbohydrates Flashcards
1
Q
What are the classifications of carbohydrates (3)
A
- Simple/complex
- Aldose/ketose
- No. of C atoms
2
Q
What is the stereochemistry of simple carbohydrates (4)
A
- All carbs are chiral
- Tetrahedral carbon is represented by two crossed lines
- Horizontal lines = bonds coming out of the page
- Vertical lines = bonds going into the page
3
Q
what are chiral objects (3)
A
- Can not be superimposed
- When placed on top of each other, are not the same
- e.g. hands
4
Q
What are D and L sugars (4)
A
- Enantiomers (mirror-image forms)
- D sugar–hydroxyl group at the bottom chiral centre pointing to the right (dextro)
- L sugar–hydroxyl group at the bottom chiral centre pointing to the left (levo)
- Not related to optical rotation
5
Q
What is hemiacetal formation (3)
A
- Rapid and reversible nucleophilic addition
- Alcohol + aldehyde = hemiacetal
- Alcohol + ketone = hemiketal
6
Q
What are cyclic hemiacetals (5)
A
- carbonyl and hydroxyl groups are in the same molecule
- intramolecular nucleophilic addition to form a cyclic hemiacetal
- Pyranose form (99%)
- Furanose form (1%)
- Furanose form of glucose less stable (more strained conformation)
7
Q
What are anomers (5)
A
- Two isomers from cyclic monosaccharides
- Alpha or beta
- Alpha = hydroxyl down
- Beta = hydroxyl up
- ABBA = Alpha Below, Beta Above
8
Q
What is optical rotation (4)
A
- The ability of a chiral molecule to rotate the plane of polarised light
- Measured in degrees (°)
- Dextrorotatory (d, +°)
- Levorotatory (l, -°)
9
Q
What is Dextrorotatory (2)
A
- d, +°
- a substance that rotates plane polarised light in a clockwise direction
10
Q
What is Levorotatory (2)
A
- l, -°
- a substance that rotates plane polarised light in an anti-clockwise direction
11
Q
What is mutarotation
A
The change in optical rotation observed when a solution of a pure single sugar anomer equilibrates to a mixture of anomers
12
Q
What are disaccharides (2)
A
- monosaccharide + alcohol = glycoside
- If the alcohol is itself a sugar, the glycosidic product is a disaccharide
13
Q
What do disaccharides contain (5)
A
- glycosidic bond between the anomeric carbon (the carbonyl carbon) of one sugar and an -OH group at any position on the other sugar
- Glycosidic bond between C1 of the first sugar and the 3. OH at C4 of the second sugar is very common
- 1,4’ link (1-4’ link)
- Glycosidic bonds can be either alpha or beta
14
Q
What is Cellobiose and Maltose (4)
A
- Reducing sugars
- Exhibit mutarotation
- Maltose has a 1,4’-alpha-glycosidic bond
- Cellobiose has a 1,4’-beta-glycosidic bond
15
Q
What are reducing and non-reducing sugars (2)
A
- Reducing = aldoses - donate electrons
- Non-reducing = 2-ketoses - under basic conditions
