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33 Cards in this Set
- Front
- Back
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What is TLC?
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a highly sensitive analytical technique used to determine the purity of a sample, determine the identity of two compounds, and monitor the progress of a reaction.
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Should every reaction in the lab be monitored by TLC?
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YES. Only need microgram quantities of sample
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what is d0, dA, and dB?
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d0-travel distance of solvent, dA - travel distance of compound A, dB - travel distance of compound B
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What are Rf values?
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distance traveled by compound divided by distance traveled by solvent.
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In what Rf range is the best resolution of the compound?
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0.3 - 0.7
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How do we see compounds under UV?
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The UV light of 254 nm is absorbed by the compounds with strong UV absorption.
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Give examples of compounds easily detected under UV
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Unsaturated ketones/aldehydes/acids/estesr
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Give examples of compounds not detected under UV light.
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Non-conjugated ketones/aldehydes/acids/esters/amides, and alkyl substituted benzene compounds
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What are two methods to visualizing compounds other than UV light?
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Vanillin stain and Iodine jar
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How does the vannillin stain work?
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Dissolving vanillin in ethanol with sulfuric acid and dipping the TLC plate into this solution, then heating the plate.
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How does the iodine jar work?
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Compounds containing a C=C will show when exposed to iodine vapor.
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What is silica gel vs. solvents used to develop TLC?
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a highly polar stationary phase/less polar moving phase
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More polar compounds interact best with _____________, giving what type of Rf values?
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Silica gel ; lower Rf values
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The use of a more polar solvent system results in the Rf value being what?
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HIGHER
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A high Rf = ? while a low Rf = ?
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fast-moving; slow-moving
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From high Rf (less polar) to low Rf (more polar) compounds
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Alkanes, alkyl halids > alkenes, aromatic hydrocarbonds, aromatic halides > esters, ethers, ketones, aldehydes > amides > alcohols > phenols > carboxylic acids
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What should you use for recrystallization? (Beaker or E. Flask?)
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Erlenmeyer flask
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How to choose solvent for recrystallization?
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Like dissolves like - common solvents are ethanol, water, methanol, ligroin, and toluene. Dissolve solvent in the better solvent, then add the poorer solvent to hot solution until saturation occurs when using a solvent-pair.
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How do you dissolve a solute for recrystallization?
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Heat the mixture to boiling while adding solvent.
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How do you decolorize a solution?
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add Norit to the solution and heat it to boiling for a few minutes while swirling. Remove Norit by filtration
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How do you filter solids?
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Filter the hot solid, adding solvent to prevent crystallization
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How do you crystallize the solute?
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Allow to cool to room temperature without disturbing. Put in ice bath if necessary.
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How do you collect crystals?
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Do suction filtration with Hirsch funnel to remove liquid.
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How do you dry crystals?
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Press against crystals with more filter paper and lay out on watch glass to dry.
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What region in IR spectra is important?
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4000-1430 cm-1 region (where most of the characteristic stretching vibration absorptions appear)
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3600-3200
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O-H; broad and very strong; intramolecular H-bonding
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3500~3300
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N-H; less borad - secondary amine, primary amide, secondary amide
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3310-3200
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triplebondC-H; strong
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3100-2700
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C-H; medium to weak; aromatic & alkenic, alkanic
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2260-2100
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Triple bonds C-C and C-N; C=C=C; sharp but weak
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1850-1620
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various C=O; very strong
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What lowers C=O and what raises C=O?
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Conjugation lowers, while ring strain raises (less ring)
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1680-1500
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various C=C and C=N
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