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28 Cards in this Set
- Front
- Back
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What is a complex carbohydrate? |
2 or more simple sugars joined together. |
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What is a disaccharide? Give an example. |
Made up of 2 monosaccharides joined together. broken down by hydrolysis. Sucrose -> glucose + fructose |
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What is a polysaccharide? Give an example. |
Made up of many monosaccharides joined together. broken down by hydrolysis. Cellulose -> 3000 glucose. |
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What is a monosaccharide? |
the simplest unit of sugar. it cannot be hydrolised into simpler compunds. They have a single carbon chain, one carbonyl group and many hydroxy groups attached to remaining carbons. |
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The two types of monosaccharides are.... |
Aldoses and ketoses. |
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How do you name a monosaccharide? |
1. aldo/keto 2. tri- , tetr- , pent-, hex- etc (depending on amount of carbons.) 3. ose |
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aldtertrose ketohexose aldpentose |
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Fisher projections of carbohydrates must.... |
1. have C=O shown at top or near top 2. Atoms stack on top of each other 3. internal carbons not shown as C |
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What is a D and L sugar? |
On fisher projection of the carbohydrate, the stereogenic centre with the OH on the left side is L, OH on right side is D. fun fact, R glyceraldehyde rotated light clockwise and was called Dextrorotatory. S glyceraldehyde was Levorotatory. |
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Does D and L relate to the direction in which a sugar rotates light? |
NO. |
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Increase in stereogenic centres result in how many stereo isomers possible? What about D and L pairs of enantiomers? |
2^n for stereoisomers (where n=amount of stereo centre carbons) D L is half of stereoisomer amount. |
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What are the rules to Haworth projections? |
1. Hs and OHs on left of fischer projection NOT involved in hemiacetyl formation is up. 2. Hs and OHs on right is down. 3. D sugar, CH2OH is up, L sugar, CH2OH is down. 4. at C1, OH and H can be up or down. |
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on haworth projection, if CH2OH is cis or trans, what form of sugar is it? What are these sugars called? |
cis = beta trans = alpha they are called anomers. |
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What are anomers? |
Diastereomers that differ only in configuration at only one asymmetric carbon. eg the beta and alpha hemiacetal forms of D glucose. |
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Define mutarotation. |
When a pure anomer is dissolved in water, there is a spontaneous change in optical rotation because the anomer equillibrates to an equilibrium mixture of anomers (Beta and alpha). This equilibrium occurs due to reverse ring opening to open chain aldehyde form, then recloses (cyclises), forming the opposite anomer. |
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During mutarotaion, what is the ratio of anomers and why? |
36:64 alpha:beta This is because if seen in the chair conformer, all substituents are equitorial, so more stable than alpha which has the OH group in the axial position. |
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Which is the most stable D-aldohexose? |
Because all OH and CH2OH are equitorial, so least sterically crowded hence most stable of all D aldohexose. |
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For the OH on the carbohydrates, how do you convert them to esters or ethers? |
ether = CH3I / Ag2O ester = (CH3CO)2O/pyridine |
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what are carbohydrate acetals called? |
glycosides. |
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Do glycosides show mutarotation? |
Like all acetals, glycosides are stable to water and are not in equillibrium with open chain form. SO does not show mutarotation. only in aqueos acid will it be converted to the free monosaccharide. |
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Name? How to form? |
react aldose (same can apply for ketose) with NaBH4, reducing the C=O to C-OH. |
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Name? How to form? |
Aldaric acid react aldose with warm dilute HNO3. Dicarboxylic acid forms. |
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Name? How to form? |
Aldonic acid, react with Benedicts reagent (Cu2+ with aq. sodium citrate). note, benedict reagent can test for reducing sugars, as these sugars reduces this reagent and forms red Cu2O. |
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When can carbonyl compounds react with acid and bases? |
They can only react if the carbon bonded to the carbonyl group (alpha carbon) has at least one H attached to it. |
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When carbonyl compound reacts with an acid, what does it form? How about base? When does it act as the nucleophile/electrophile? Mechanisms? |
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Why is enolate anion stable? |
Due to delocalization of charge. |
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What is tautomerism? |
Isomers with their atoms arranged differently and rapidly interconvert. Most monocarbonyl compounds exist almost entirely in their keto form, even less enol for RCOOH, RCOOR, RCONR. |
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what is aldol condensation? how to form enal compounds? is this stable? why? |
aldol = aldehyde + alcohol. condensation = loss of H2O, remember that elimination of OH and H (must be from alpha carbon) from the aldol molecule forms the enal. to form aldol, react carbonyl compound in strong basic conditions, remember that 2 mols react, and the anion one attacks the carbonyl carbon. |
