Carbohydrates - Naming & Classification:

Carbohydrates Carbohydrates - Naming & Classification: Carbohydrates refer to chemical compounds that are composed of carbon atoms that are fully hydrated and typically follow the formula Cn(H2O)n Can be thought of as a 1:2:1 ratio between carbons:hydrogens:oxygen These molecules fulfill the body’s energy requirements (such as glucose) The suffix -ose is the one used for sugars (cellulose, ribose, and even glucose) In order to name sugars, start counting from the functional group at the top (such as glyceraldehyde being a triose) 3 carbons → triose 4 carbons → threose/tetrose 5 carbons → pentose 6 carbons → hexose You can change the functional group at the top of the structure and it will alter the type of sugar it is while keeping the chemical formula the same (such as changing the aldehyde group in glucose to a ketone group converts the sugar to a fructose molecule) Aldo- is if the functional groups in the carbohydrate is an aldehyde (glucose is an aldohexose) Keto is if the functional group in the carbohydrate is a ketone (fructose is a ketohexose) Fructose is a hexose with a ketone functional groups (known as a ketohexose) Next, you go to the highest numbered chiral carbon and if on a fischer projection the -OH is on the right then it has D stereochemistry (same as R) and if the -OH is on the left then it has L stereochemistry (same as S) Glucose has D stereochemistry Carbohydrates - Absolute Configuration, Epimers, Common Names: Humans are evolutionary made to break down D sugars D and L configurations differ at EVERY chiral center, not just the last one that we used in order to determine its stereochemistry This means that they are TRUE enantiomers meaning that they are perfect mirror images of one another D sugars also have varying diastereomers (where only one OH position is flipped in comparison to glucose) Epimers are diastereomers that differ at only one chiral carbon (such as DGalactose and D-Glucose) If there are 4 chiral centers then there are 24 = 16 stereoisomers (where half (8) are D and half (8) are L, with diastereomers of each) Some common monosaccharides to know: Carbohydrates - Cyclic Structures & Anomers: Carbohydrates basically have the carbonyl/alcohol organic chemistry reactions waiting to happen (alcohol is the nucleophile and the carbonyl is the electrophile) Remember, an Acetal is ROCOR (cannot be further reduced) and a Hemiacetal is HOCOR (can be reduced to an acetal) Once the oxygen loses its proton, it has an extra set of electrons that can nucleophilically attack the carbon of the carbonyl group, making the double bonds bump up and use its newly acquired electrons to grab onto a proton (shown on the right) The most stable ring formed is a 6 membered ring, which is why that specific oxygen attacks A six membered sugar ring is called a pyranose (5 carbons in the ring and an oxygen) A five membered sugar ring is called a furanose (4 carbons in the ring and an oxygen) Anomeric carbon is the chiral carbon that we use in order to nucleophically attack (the one in the functional group and if it is down then alpha and up then beta in the haworth diagram) Haworth Diagram shows the 2D structural layout of the atoms but a Chair diagram shows its different configurations as they would appear in 3D space “Downright, uplefting” shows that the ones on the right of the fischer diagram will be pointed down in the haworth diagram while those on the left will be pointed up If it is a D sugar then the last carbon (C6) will point up Also, going from fischer to chair makes the process much easier Mutarotation is when the sugar goes back and forth from alpha/beta conformations (beta is favored 64% while alpha is favored 36%) Also, if it is on the right of a fischer projection, then it is R and left is S Carbohydrates - di & polysaccharides: Carbohydrates can link together to form acetals known as glycosidic linkages These glycosidic linkages occur between C1 (anomeric carbon) and C4 of the next sugar Known as 1-4 glycosidic linkage (alpha for trans or beta for cis) Alpha/Beta also means what the saccharide is in the preceding sugar Lactose is made up of glucose and galactose joined together by a beta 1,4 glycosidic bond Maltose is made up of two glucose molecules joined together by an alpha 1,4 glycosidic bond Sucrose (table sugar) is one of the most common sugars in all of nature and is made up of glucose and fructose (which is a furanose) and is linked by their two anomeric carbons (unique) making it a nonreducing sugar Cellulose is made up of repeating glucose units joined by beta 1,4 glycosidic bonds (forms an unbranched straight chain and we can’t break this down because we don’t have the enzyme to break down beta glycosidic bonds) Starch is made up of repeating glucose units joined by alpha 1,4 glycosidic bonds (we can break this down because our enzymes will break down alpha bonds) → you can branch with more glucose molecules if you attach to the C6 side (creating an alpha 1,6 linkage) This is basically known as glycogen (stores energy) Keto-enol Tautomerization (by Jay): Enol refers to the double bond between to C atoms with an alcohol on the outside Aldehyde and enol are isomers of one another (not resonance structures) Alpha carbon is the one on the left of the double bond in the picture → Enolate anion occurs when the oxygen is not protonated The oxyanion contributes much more to the structure than the carbanion because oxygen is much more electronegative than carbon, allowing it to endure the negative charge better When the alpha carbon is chiral, you can get racemization where both S and R configurations are present (shown on the bottom right) Also, remember the keto form is favored when compared to the enol form (unless there is an aromatic ring that forms which could make the enol form more stable) Extra Notes: IR peaks you should know: 1760 cm-1 - 1165 cm-1 is indicative of two different carbonyl functional groups Amylopectin is like glycogen where it is repeating subunits of glucose