Organic Chem Test Questions

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simiple sugars.
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C(H2O)
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carbohydrates include
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polyhydroxyaldehydes, polyhydroxyketones, and compounds taht are easily hydrolyzed to them
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monosaccarides
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cannot be hydrolyzed further
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Glucose
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is a polyhydroxyaldehyde. are called aldoses
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fructose
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is a polyhydroxyketone. and are called toses.
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The aldehyde carbon
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is the most highly oxidized and numbered 1 in the IUPAC name. so it’s always at the tope of the Fisher projection
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the Ketosies
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the carbonyl group is usually the second carbon from the top.
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Fisher projection
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horizontal bonds are projected out. Vertical bonds are projected away. The most oxidized carbon is always at the top.
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simple sugars (mono)
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glucose, fructose. sweet taste
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disaccarides such as sucrose (table sugar)
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are molecules of one glucose adn one fructose. sweet taste
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polysaccarides (such as starch)
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can by hydrolized to 1000’s of glucose.
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Classification on monosaccharides
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3 criteria: whether the sugar contianes ketone or aldehyde group. 2. # of carbon atoms in the carbon chain. 3. stereochemical configuration o fthe asymmetric carbon atom farthest from teh carbonyl group.
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Classification on monosaccharides (cont.)
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TRIOSE, TETROSE, PENTOSE, HEXOSE, HEPTOSE. example glucose (6 carbon aldehyde)=aldohexose. Fructose (six carbon ketone)=ketohexose.
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Natural sugars
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have D rotation.- have the OH group of he bottom asymmetric carbon on the right
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Pg. 1101. Start with D(+)-glyceraldehyde
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will make 14 other compounds by adding C to it.
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Erythrose and Threo
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a diastereomer is erythro if its fischer projection shows similar groups on teh same side of the molecule. Threo= if similar groups are on opposite sides of the fischer projection. (pg. 1102)
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diastereomers
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2R, 3S= 2S, 3R
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2R, 3R=2S, 3S.
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erythor and threo (for dissymetric)
meso, d,l for symmetric molecules
(Pg. 1103)
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generally used only with molecuels that do not have symmetric ends.
MESO is used and (d,l) indicated the diasteromer and tell whether or not it has an enantiomer.
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epimers
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sugars that differ only by the stereochemistry at a single carbon. it is generally stated (if not stated it is assumer C2.
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cyclic hemiacetals
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when an alcohol and aldehyde is on the same chain of a 5-6 carbon chain it forms a cyclic hemiacetal. the cyclic form is more stable than a chain.
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to do hemiacetal= know how to go from fisher projection to ring to chair conformation
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turn fisher projection to the right (aldehyde #1 is pointed towards us when turned to the right), OH is as follows on fisher (up = up, down=down). rotate so that 6 and 5 switch places and then do hemiacetal (Haworth projection is flat). You will then write chair conformer format. C1 always connected to 2 oxygen (one within the ring and one as an OH group). C1 can be axial or equatorial. PG. 1105 example of glucose
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Hemiacetal
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for D confirmation the rotation from fisher to haworth projection puts the terminal -CH2OH upwards.
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pyranose, furanose
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pyranose= 6 membered rings
furanose= 5 membered rings= flat haworth projection
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anomers
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the flipping of C1 OH group in cyclic hemiactetals (both 5 and 6 membered rings)
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down(axial) = alpha anomer
up (equatorial)= beta anomer
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mutarotaion
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occurs because the two anomers interconvert in solution. when either of the pure anomers dissolves in water, its roation dragually changes to an intermediate roation that results from equilibrium concentrations of the anomers
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epimerization (by base catylized)
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abstraction alpha protron (C2) Hydrogen causes OH to switch arrangement
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enediol rearrangement= makes ketone on C2 carbon
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Removes the alapha proton, reprotonates oxygen to give enediol, deprotonates teh oxygen on C2, reprotonates on C1 to give the ketose (pg 1111-1112)
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using BASE with sugars gets alot of enediol and epimerization side reactions!!
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unless using protective groups
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reduction of monosaccharides
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turns cyclic rings back to chain and keeps reducing chain. reduces chain from aldehyde or ketone by getting rid of double bond and anding Hyrdogen. (H2, Ni for aldehydes) or (NaBH4 for ketones *makes epimers!)
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bromine water
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is used to oxidize ALDEHYDES! it does not oxidize ketones and does not cause epimerization or rearrangement o fthe carbonyl group. it can be used to distinguish aldoses adn ketoses. the product is aldonic acid (liek gluconic acid)(ex: pag 1114, -CHO turns to -COOH)
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HNO3= oxidizer of aldehydes and terminal group -CH2OH
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is a stonger oxidizer than Br2 and water. so it oxidizes both aldehyde and terminal group -CH2OH. produces aldaric acid (ex: glycaric acid) Turns -CHO and -CH2OH to (COOH and COOH)
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Tollens test (2 Ag(NH3)2 and -OH
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does not distiguish between aldehyde or ketone. it is used to find if it is in ring form or chain form. Tollens will not react if it’s in ring form. reaction gives off metallic silver.
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glycosides
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are sugars in teh form of acetals. -osides. ex: glucoside. if it’s a six memebered ring: glucopyranoside. five ring = ribofuranoside. C1 carbon -OCH3
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to form glycosides.
*remember from chain used -OH and acid cat.
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us ROH and H+. it will replace C1 -OH with -OR group. will form both beta and alpha equally.
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aglycone
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is the group bonded to the anomeric carbon (C1) of the glycoside.
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Ether
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sugars have a lot of -OH groups. Use (CH3I and Ag2O excess) to replace all H of -OH group with CH3. ex: -OH is then converted to OCH3 (all of them in the ring).
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ester formation
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Replaces all -OH group with -OC(R)=O group. Uses acetic ANHYDRIDE and pyridine (excess (CH3CO)2O. (it takes part of the anhydride and connects to -O.
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osazone (H2NNH-phenly)
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substance will work on both aldehyde and ketone C1 and C2!. Does not effect below C2. so the effects on C1 and C1 is =NNH(PH).
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Chain shortening: Ruff degradation (aldehyde)
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Starts by Bromine water (Br2, H20) to get aldonic acid then treats with hydrogen peroxide adn ferric sulfate. the result is -CHO as C1 and one C shorter than what it started out with. ex: page. 1120-1121
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Kiliani-Fischer synthesis (lengthens an aldose carbon chain.
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Adds one carbon atom to the aldehyde end of the aldose. the former C1 is now C2. The end result is -CHO added. Materials used HCN/KCN –> H2/pd/BaSO4 –> H3O+
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clues that told Fischer the correct type of glucose (CLUE 1)
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clue 1: on ruff degradation, glucose and mannose give the same aldopentose: D-(-)-arabinose. this suggests that glucose and mannose are C2 epimers (confirmed by treating with phenylhydrazine and showing it gives the same osazone.
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CLUE 2
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on ruff degradation D-(-) arabinose give the aldotetrose D-(-) erythrose. upon treatment with nitric acid, erythrose gives an opticaly inactive aldaric acid (meso). this means D-erythrose, botained from ruff degradation of D-aldopentose, mut be a D-aldotetrose.
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CLUE 3
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on oxidation with nitric acid D(-) arabinose gives an optically active aldaric acid. The means, of the two structures for D-arabinose, only the second would oxidize to giv an optically active aldaric acid. the other structure must be arabinose
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CLUE 4
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when the -CHO and -CH2OH groups od D-mannose are interchanged, the product is still D-mannose. when the -CHO and -CH2OH groups of D-glucose are interchanged, the product is an unnatural L sugar. Meaning, if the two end groups of structure X are interchanged, the product looks strange. when we rotate 180 degrees it is the same.
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determination of ring size
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must treat ring with CH3I (RI) and Ag2O in excess–> H+ (H3O). this breaks the O (in the ring) bond with C5. it gets it back into a strain chain form (pg. 1128)
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cleavage with HIO4, H+
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disaccarhides
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can link at 1, 4′ or 1, 6′, or 1, 1′. all through O
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most common is 1, 4′
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cellobiose(beta), maltose(alpha),lactose(beta).
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1, 6′ : Gentiobiose
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sucrose
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1, 1′ linkage (one glucose and one fructose, 6 and 5 memebered rings.) sucrose does not reduce tollens reagent and it cannot mutarotate
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Maltose
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alpha-1,4′ link with two glucose units.
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Cellobiose
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beta- 1, 4′ link with 2 glucose units. C4 OH is in alpha position
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Lactose
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beta 1, 4′ linkage with 2 glucose. C4 OH group is in beta position
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Polysaccharieds
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does not react with tollens reagent, and they do not mutarotate
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nucleic acid
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backbone is ribofuranoside (five membered ring)linked by phosphate ester groups.
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RNA
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two class: moncyclic (cytidine, uridine)(also pyrimidine)
bicyclic: adenine and guanine (also purine)
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AT, CG
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