carbs

• monosaccharides

  • A source of energy in metabolic processes
  • have the general formula Cn(H2O)n, where n varies from 3 to 8
  • Aldose: A monosaccharide containing an aldehyde group
  • Ketose: A monosaccharide containing a ketone group

  A) aldose

  B) ketose

  
• naming monosaccharides

  • prefix: number of carbons in molecule
  • suffix: ose, indicates that it is a carbohydrate

  A) triose

  
• silver mirror test

  • used to detect the presence of aldehydes
  • based on the reduction of silver ions to silver metal, which forms the mirror
  • Tollens' reagent selectively oxidises aldehydes but not ketones
  • conclusion: if an aldehyde is present, silver forms because aldehyde is oxidised to carboxyl group ALLOWING Ag+ in Tollens' reagent to reduce to Ag solid.
  • on the other hand, if ketones were present, nothing would occur as it cannot undergo oxidation, preventing Ag+ to reduce.
• carbohydrates

  • carbohydrate = hydrated carbon atom (has H & OH's)
  • small carbohydrates = sugars (name ends in "ose")
  • monosaccharide names: triose, tetrose, pentose, hexose
  • these monosacch. will either have ketone or aldehyde functional group ("aldose" or "ketose")

  A) aldohexose

  B) ketopentose

  
• fischer projection

  • a way to represent 3D molecules in a 2D format (usually with carbohydrates and amino acids)
  • emphasizing the stereochemistry of chiral centers

  A) wedge

  B) dash

  
• D vs L sugars

  1. look at the SECOND LAST carbon
  2. if the -OH points right, it's ( D )
  3. if the -OH points left, it's ( L )

  helps differentiate between enantiomers of sugar molecules

  A) d

  B) l

  
• monosaccharides

  • exist in an equilibrium between linear or cyclic compounds (cyclic more common)
  • they form cycles by an intramolecular hemiacetal formation
  • hemiacetal forms because an alcohol attacks an aldehyde or ketone (ie. intramolecular cycling)

  
• monosaccharides - link with number of stereoisomers

  1. starts with 2 glyceraldehydes (D and L, one chiral centre)
  2. then 4 aldotetroses (2D and 2L, two chiral centres)
  3. then 8 aldopentoses (4D and 4L, three chiral centres)
  4. then 16 aldohexoses (8D and 8L, four chiral centres)

  note: image only shows D, not L

  
• D glucose

  • aldehyde group
  • hydroxyl group: right, left, right, right (going down)

  
• glucose and fructose

  • glucose is an aldose
  • fructose is a ketose

  A) fructose

  
• glucose and galactose

  • epimer: diastereomers that differ only at ONE chiral centre (diast. differ at at least one chiral centre)
  • galactose is the C-4 epimer of glucose

  A) galactose

  B) glucose

  
• cyclic glucose

  1. react with acid (H+) to activate aldehyde (turns to -COOH)
  2. -OH group on 5th carbon will attack the carboxyl group
  3. this breaks the pi bond (sp2),
  4. the molecule bends into hexagon. If -OH group on right, it points down, if -OH group on left, it points up
  5. the OH, H and CH2OH will rotate to be in correct orientation
  6. when -OH alings with -COOH, it will form a or b glucose

  
• chain to cyclic glucose

  A) CH2OH

  B) H

  C) H

  
• hamiacetals

  • Aldehydes and ketones react with alcohols to form hemiacetals
  • this leads to a molecule with an (-OH) group and an ether group on the same carbon atom

  
• Haworth projection

  • this is a way of showing 3D cyclic molecules as 2D, helping to understand the stereochemistry
  • linear form = less stable, cyclic form = more stable

  
• anomers

  • definition: a pair of stereoisomers, usually sugars, that differ due to the configuration of the -OH group
  • anomeric carbon: the new stereocentre resulting from cyclic hemiacetal formation

  A) b

  B) a

  C) cis

  D) trans

  
• infixes

  • 6 hemiacetal ring has -pyran- infix (hexagon)
  • 5 hemiacetal ring has -furan- infix (pentagon)

  A) pyran

  B) furan

  
• chair conformation

  • for furanoeses (5): planar representation
  • for pyranoses (6): chair conformation
  • axial position: when an atom or group is bonded vertically up or down (usually small atoms - H)
  • equatorial position: when an atom or group is bonded diagonally (usually larger groups - OH)

  A) equatorial

  
• b-D-GLUCOSE (haworth projection --> chair conformation)

  1. horizontal timelapse, with O in top right (hemiacetal bond)
  2. label the carbon numbers. 1 is the anomeric carbon, 6 is the CH2OH
  3. order atoms/groups in axial or equatorial position (using rule)
  4. a-glucose = -OH group in axial position on 1st carbon
  5. b-glucose = -OH group in equatorial position on 1st carbon

  A) equatorial

  B) chair

  C) haworth

  
• why is b-glucose more common?

  • the equatorial position is always more stable
  • more stable by minimising steric hindrance
  • basically means the repulsions of electrons in b-glucose are more stable than a-glucose
  • this is because the -OH groups are all in equatorial positions, hence more stable and more common
• mutorotation

  • where a solution of a cyclic compound (eg. glucose) changes its rotation due to the equilibrium between its α and β anomers (due to the ring opening and closing)
  • b-D-glucose rotates plane polarised light by +18.7 degrees
  • a-D-glucose rotates it by +112 degrees
  • if b-glucose is put in water, its rotation changes from 18.7 to 52.7, and a will decrease to 52.7, telling us that both forms exist but more B anomer

  
• disaccharides - glycoside formation

  • -OH of the anomeric carbon is replaced by –OR (acetal formation)
  • the OH on glucose and OH on methanol forms an acetal group (not ether) connected by glycoside bond
  • cyclic acetals are NOT in equilibrium, so they do not undergo mutarotation (cannot change between a/b forms)

  A) glycoside

  B) anomeric

  
• disaccharides

  • sugars are alcohols so they can bind to each other
  • a-1,4'-glycoside bond
  • "a-1" means the start of the bond is from the 1st carbon of alpha molecule
  • "4'-glycoside bond" means the bond connects from the 4th carbon on the other molecule

  
• more examples

  A) b

  B) a

  
• N-glycosides

  • The anomeric carbon of a cyclic hemiacetal also reacts with the N-H group of amine to form an N-glycoside

  A) anomeric

  B) glycoside

  
• sucrose disaccharide

  • fructose + glucose
  • here, the glycoside bond is a & b because it's a-glucose + b-fructose

  A) a

  B) 1

  
• Polysaccharides

  • the red squiggle means its a chain, so the molecule continues
  • cellulose is made of only b-glucose

  A) 4

  B) 1

  C) starch

  
• cellulose

  • provides structure in plants due to its rigid structure
  • has a linear chain connected by strong hydrogen bonding
  • the D-glucose units are joined by b-1,4 links

  
• starch

  • fully digestible (unlike cellulose) and only present in plants
  • eg. beans, wheat, rice, potatoes
  • D-glucose is joined by a-1,4 links

  
• starch - amylose

  • amylose makes up 20% of starch
  • amylose coils into helices and forms a linear chain
  • contains only a-1,4 links
  • soluble in hot water

  
• starch - amylopectin

  • amylopectin makes up 80% of starch
  • amylopectin forms a branched structure (higher surface area)
  • contains a-1,4 and a-1,6 links
  • insoluble in water

  
• glycogen

  • stores energy in animals in the liver and muscles
  • similar to amylopectin in being a long polymer of D-glucose with the same type of links
  • same as amylopectin but with MORE branches

  A) plants

  B) animals

  
• mutarotation (commonly tested)

  • applies only when in a SOLUTION
  • when glucose dissolves in water, it forms an equilibrium of a and b forms because the cyclic ring opens and closes
  • optical rotation: the way light bends when it passes through solution
  • a and b glucose bend light in different angles, helping scientists
  • eg. 1) b-glucose put in water, 2) -O- bond goes back to -OH (6th carbon) and -COOH (1st carbon) 3) carboxyl group flips 180 4) reform -O- bond but now it's a-glucose